Kurt Allen Krobert

• Levay, Magdolna K.; Krobert, Kurt Allen; Vogt, Andreas; Ahmad, Atif; Jungmann, Andreas & Neuber, Christiane [Show all 11 contributors for this article] (2022). RGS3L allows for an M<inf>2</inf> muscarinic receptor-mediated RhoA-dependent inotropy in cardiomyocytes. Basic Research in Cardiology. ISSN 0300-8428. 117:8(1), p. 1–21. doi: 10.1007/s00395-022-00915-w. Full text in Research Archive Show summary

  Abstract The role and outcome of the muscarinic M 2 acetylcholine receptor (M 2 R) signaling in healthy and diseased cardiomyocytes is still a matter of debate. Here, we report that the long isoform of the regulator of G protein signaling 3 (RGS3L) functions as a switch in the muscarinic signaling, most likely of the M 2 R, in primary cardiomyocytes. High levels of RGS3L, as found in heart failure, redirect the G i -mediated Rac1 activation into a G i -mediated RhoA/ROCK activation. Functionally, this switch resulted in a reduced production of reactive oxygen species (− 50%) in cardiomyocytes and an inotropic response (+ 18%) in transduced engineered heart tissues. Importantly, we could show that an adeno-associated virus 9-mediated overexpression of RGS3L in rats in vivo, increased the contractility of ventricular strips by maximally about twofold. Mechanistically, we demonstrate that this switch is mediated by a complex formation of RGS3L with the GTPase-activating protein p190RhoGAP, which balances the activity of RhoA and Rac1 by altering its substrate preference in cardiomyocytes. Enhancement of this complex formation could open new possibilities in the regulation of the contractility of the diseased heart.

• Melsom, Elin Maria Caroline Bull; Cosson, Marie-Victoire; Ørstavik, Øivind; Lai, Ngai Chin; Hammond, H. Kirk & Osnes, Jan-Bjørn [Show all 10 contributors for this article] (2019). Constitutive inhibitory G protein activity upon adenylyl cyclase-dependent cardiac contractility is limited to adenylyl cyclase type 6. PLOS ONE. 14:e021810(6), p. 1–19. doi: 10.1371/journal.pone.0218110. Full text in Research Archive Show summary

  Purpose We previously reported that inhibitory G protein (Gi) exerts intrinsic receptor-independent inhibitory activity upon adenylyl cyclase (AC) that regulates contractile force in rat ventricle. The two major subtypes of AC in the heart are AC5 and AC6. The aim of this study was to determine if this intrinsic Gi inhibition regulating contractile force is AC subtype selective. Methods Wild-type (WT), AC5 knockout (AC5KO) and AC6 knockout (AC6KO) mice were injected with pertussis toxin (PTX) to inactivate Gi or saline (control).Three days after injection, we evaluated the effect of simultaneous inhibition of phosphodiesterases (PDE) 3 and 4 with cilostamide and rolipram respectively upon in vivo and ex vivo left ventricular (LV) contractile function. Also, changes in the level of cAMP were measured in left ventricular homogenates and at the membrane surface in cardiomyocytes obtained from the same mouse strains expressing the cAMP sensor pmEPAC1 using fluorescence resonance energy transfer (FRET). Results Simultaneous PDE3 and PDE4 inhibition increased in vivo and ex vivo rate of LV contractility only in PTX-treated WT and AC5KO mice but not in saline-treated controls. Likewise, Simultaneous PDE3 and PDE4 inhibition elevated total cAMP levels in PTX-treated WT and AC5KO mice compared to saline-treated controls. In contrast, simultaneous PDE3 and PDE4 inhibition did not increase in vivo or ex vivo rate of LV contractility or cAMP levels in PTX-treated AC6KO mice compared to saline-treated controls. Using FRET analysis, an increase of cAMP level was detected at the membrane of cardiomyocytes after simultaneous PDE3 and PDE4 inhibition in WT and AC5KO but not AC6KO. These FRET data are consistent with the functional data indicating that AC6 activity and PTX inhibition of Gi is necessary for simultaneous inhibition of PDE3 and PDE4 to elicit an increase in contractility. Conclusions Together, these data suggest that AC6 is tightly regulated by intrinsic receptor-independent Gi activity, thus providing a mechanism for maintaining low basal cAMP levels in the functional compartment that regulates contractility.

• Cosson, Marie-Victoire; Hiis, Halvard Gautefall; Moltzau, Lise Roman; Levy, Finn Olav & Krobert, Kurt Allen (2019). Knockout of adenylyl cyclase isoform 5 or 6 differentially modifies the ? &lt;sub&gt;1&lt;/sub&gt; -adrenoceptor-mediated inotropic response. Journal of Molecular and Cellular Cardiology. ISSN 0022-2828. 131, p. 132–145. doi: 10.1016/j.yjmcc.2019.04.017. Full text in Research Archive
• Hiis, Halvard Gautefall; Cosson, Marie-Victoire; Dahl, Christen Peder; Fiane, Arnt E; Levy, Finn Olav & Andersen, Geir Øystein [Show all 7 contributors for this article] (2018). Hypothermia elongates the contraction-relaxation cycle in explanted human failing heart decreasing the time for ventricular filling during diastole. American Journal of Physiology. Heart and Circulatory Physiology. ISSN 0363-6135. 315(5), p. H1137–H1147. doi: 10.1152/ajpheart.00208.2018. Full text in Research Archive Show summary

  Targeted temperature management is part of the standardized treatment for patients in cardiac arrest. Hypothermia decreases cerebral oxygen consumption and induces bradycardia; thus, increasing the heart rate may be considered to maintain cardiac output. We hypothesized that increasing heart rate during hypothermia would impair diastolic function. Human left ventricular trabeculae obtained from explanted hearts of patients with terminal heart failure were stimulated at 0.5 Hz, and contraction-relaxation cycles were recorded. Maximal developed force (Fmax), maximal rate of development of force [(dF/dt)max], time to peak force (TPF), time to 80% relaxation (TR80), and relaxation time (RT = TR80 − TPF) were measured at 37, 33, 31, and 29°C. At these temperatures, stimulation frequency was increased from 0.5 to 1.0 and to 1.5 Hz. At 1.5 Hz, concentration-response curves for the β-adrenergic receptor (β-AR) agonist isoproterenol were performed. Fmax, TPF, and RT increased when temperature was lowered, whereas (dF/dt)max decreased. At all temperatures, increasing stimulation frequency increased Fmax and (dF/dt)max, whereas TPF and RT decreased. At 31 and 29°C, resting tension increased at 1.5 Hz, which was ameliorated by β-AR stimulation. At all temperatures, maximal β-AR stimulation increased Fmax, (dF/dt)max, and maximal systolic force, whereas resting tension decreased progressively with lowering temperature. β-AR stimulation reduced TPF and RT to the same extent at all temperatures, despite the more elongated contraction-relaxation cycle at lower temperatures. Diastolic dysfunction during hypothermia results from an elongation of the contraction-relaxation cycle, which decreases the time for ventricular filling. Hypothermic bradycardia protects the heart from diastolic dysfunction and increasing the heart rate during hypothermia should be avoided.

• Andressen, Kjetil Wessel; Ulsund, Andrea Hembre; Krobert, Kurt Allen; Lohse, Martin J.; Bünemann, Moritz & Levy, Finn Olav (2017). Related GPCRs couple differently to Gs: preassociation between G protein and 5-HT7 serotonin receptor reveals movement of Gαs upon receptor activation. The FASEB Journal. ISSN 0892-6638. 32(2), p. 1059–1069. doi: 10.1096/fj.201700486R. Full text in Research Archive
• Braadland, Peder; Grytli, Helene Hartvedt; Ramberg, Håkon Andre; Katz, Betina; Kellmann, Ralf & Gauthier-Landry, louis [Show all 18 contributors for this article] (2016). Low β2-adrenergic receptor level may promote development of castration resistant prostate cancer and altered steroid metabolism. OncoTarget. 7(2), p. 1878–1894. doi: 10.18632/oncotarget.6479. Full text in Research Archive Show summary

  The underlying mechanisms responsible for the development of castration-resistant prostate cancer (CRPC) in patients who have undergone androgen deprivation therapy are not fully understood. This is the first study to address whether β2-adrenergic receptor (ADRB2)- mediated signaling may affect CRPC progression in vivo. By immunohistochemical analyses, we observed that low levels of ADRB2 is associated with a more rapid development of CRPC in a Norwegian patient cohort. To elucidate mechanisms by which ADRB2 may affect CRPC development, we stably transfected LNCaP cells with shRNAs to mimic low and high expression of ADRB2. Two UDP-glucuronosyltransferases, UGT2B15 and UGT2B17, involved in phase II metabolism of androgens, were strongly downregulated in two LNCaP shADRB2 cell lines. The low-ADRB2 LNCaP cell lines displayed lowered glucuronidation activities towards androgens than high-ADRB2 cells. Furthermore, increased levels of testosterone and enhanced androgen responsiveness were observed in LNCaP cells expressing low level of ADRB2. Interestingly, these cells grew faster than high-ADRB2 LNCaP cells, and sustained their low glucuronidation activity in castrated NOD/SCID mice. ADRB2 immunohistochemical staining intensity correlated with UGT2B15 staining intensity in independent TMA studies and with UGT2B17 in one TMA study. Similar to ADRB2, we show that low levels of UGT2B15 are associated with a more rapid CRPC progression. We propose a novel mechanism by which ADRB2 may affect the development of CRPC through downregulation of UGT2B15 and UGT2B17.

• Ørstavik, Øivind; Manfra, Ornella; Andressen, Kjetil Wessel; Andersen, Geir Øystein; Skomedal, Tor & Osnes, Jan-Bjørn [Show all 8 contributors for this article] (2015). The inotropic effect of the active metabolite of levosimendan, OR-1896, is mediated through inhibition of PDE3 in rat ventricular myocardium. PLOS ONE. 10(3). doi: 10.1371/journal.pone.0115547. Full text in Research Archive Show summary

  Aims We recently published that the positive inotropic response (PIR) to levosimendan can be fully accounted for by phosphodiesterase (PDE) inhibition in both failing human heart and normal rat heart. To determine if the PIR of the active metabolite OR-1896, an important mediator of the long-term clinical effects of levosimendan, also results from PDE3 inhibition, we compared the effects of OR-1896, a representative Ca2+ sensitizer EMD57033 (EMD), levosimendan and other PDE inhibitors. Methods Contractile force was measured in rat ventricular strips. PDE assay was conducted on rat ventricular homogenate. cAMP was measured using RII_epac FRET-based sensors. Results OR-1896 evoked a maximum PIR of 33±10% above basal at 1 μM. This response was amplified in the presence of the PDE4 inhibitor rolipram (89±14%) and absent in the presence of the PDE3 inhibitors cilostamide (0.5±5.3%) or milrinone (3.2±4.4%). The PIR was accompanied by a lusitropic response, and both were reversed by muscarinic receptor stimulation with carbachol and absent in the presence of β-AR blockade with timolol. OR-1896 inhibited PDE activity and increased cAMP levels at concentrations giving PIRs. OR-1896 did not sensitize the concentration-response relationship to extracellular Ca2+. Levosimendan, OR-1896 and EMD all increased the sensitivity to β-AR stimulation. The combination of either EMD and levosimendan or EMD and OR-1896 further sensitized the response, indicating at least two different mechanisms responsible for the sensitization. Only EMD sensitized the α1-AR response. Conclusion The observed PIR to OR-1896 in rat ventricular strips is mediated through PDE3 inhibition, enhancing cAMP-mediated effects. These results further reinforce our previous finding that Ca2+ sensitization does not play a significant role in the inotropic (and lusitropic) effect of levosimendan, nor of its main metabolite OR-1896.

• Impellizzeri, Agata Antonina Rita; Pappalardo, Matteo; Basile, Livia; Manfra, Ornella; Andressen, Kjetil Wessel & Krobert, Kurt Allen [Show all 9 contributors for this article] (2015). Identification of essential residues for binding and activation in the human 5-HT7(a) serotonin receptor by molecular modeling and site-directed mutagenesis. Frontiers in Behavioral Neuroscience. 9(MAY). doi: 10.3389/fnbeh.2015.00092. Full text in Research Archive Show summary

  The human 5-HT7 receptor is expressed in both the central nervous system and peripheral tissues and is a potential drug target in behavioral and psychiatric disorders. We examined molecular determinants of ligand binding and G protein activation by the human 5-HT7(a) receptor. The role of several key residues in the 7th transmembrane domain (TMD) and helix 8 were elucidated combining in silico and experimental mutagenesis. Several single and two double point mutations of the 5-HT7(a) wild type receptor were made (W7.33V, E7.35T, E7.35R, E7.35D, E7.35A, R7.36V, Y7.43A, Y7.43F, Y7.43T, R8.52D, D8.53K; E7.35T-R7.36V, R8.52D-D8.53K), and their effects upon ligand binding were assessed by radioligand binding using a potent agonist (5-CT) and a potent antagonist (SB269970). In addition, the ability of the mutated 5-HT7(a) receptors to activate G protein after 5-HT-stimulation was determined through activation of adenylyl cyclase. In silico investigation on mutated receptors substantiated the predicted importance of TM7 and showed critical roles of residues E7.35, W7.33, R7.36 and Y7.43 in agonist and antagonist binding and conformational changes of receptor structure affecting adenylyl cyclase activation. Experimental data showed that mutants E7.35T and E7.35R were incapable of ligand binding and adenylyl cyclase activation, consistent with a requirement for a negatively charged residue at this position. The mutant R8.52D was unable to activate adenylyl cyclase, despite unaffected ligand binding, consistent with the R8.52 residue playing an important role in the receptor-G protein interface. The mutants Y7.43A and Y7.43T displayed reduced agonist binding and AC agonist potency, not seen in Y7.43F, consistent with a requirement for an aromatic residue at this position. Knowledge of the molecular interactions important in h5-HT7 receptor ligand binding and G protein activation will aid the design of selective h5-HT7 receptor ligands for potential pharmacological use.

• Andressen, Kjetil Wessel; Manfra, Ornella; Brevik, Christian Hellesylt; Ulsund, Andrea Hembre; Vanhoenacker, Peter & Levy, Finn Olav [Show all 7 contributors for this article] (2015). The atypical antipsychotics clozapine and olanzapine promote down-regulation and display functional selectivity at human 5-HT7 receptors. British Journal of Pharmacology. ISSN 0007-1188. 172(15), p. 3846–3860. doi: 10.1111/bph.13169. Full text in Research Archive
• Melsom, Elin Maria Caroline Bull; Hussain, Rizwan; Ørstavik, Øivind; Aronsen, Jan Magnus; Sjaastad, Ivar & Skomedal, Tor [Show all 9 contributors for this article] (2014). Non-classical regulation of β1- and β2 adrenoceptor- mediated inotropic responses in rat ventricle by the G protein Gi. Naunyn-Schmiedeberg's Archives of Pharmacology. ISSN 0028-1298. 387(12), p. 1177–1186. doi: 10.1007/s00210-014-1036-7. Full text in Research Archive
• Melsom, Elin Maria Caroline Bull; Ørstavik, Øivind; Osnes, Jan-Bjørn; Skomedal, Tor; Levy, Finn Olav & Krobert, Kurt Allen (2014). Gi proteins regulate adenylyl cyclase activity independent of receptor activation. PLoS Medicine. ISSN 1549-1277. 9:e0106608(9). doi: 10.1371/journal.pone.0106608. Full text in Research Archive Show summary

  Background and purpose Despite the view that only β2- as opposed to β1-adrenoceptors (βARs) couple to Gi, some data indicate that the β1AR-evoked inotropic response is also influenced by the inhibition of Gi. Therefore, we wanted to determine if Gi exerts tonic receptor-independent inhibition upon basal adenylyl cyclase (AC) activity in cardiomyocytes. Experimental approach We used the Gs-selective (R,R)- and the Gs- and Gi-activating (R,S)-fenoterol to selectively activate β2ARs (β1AR blockade present) in combination with Gi inactivation with pertussis toxin (PTX). We also determined the effect of PTX upon basal and forskolin-mediated responses. Contractility was measured ex vivo in left ventricular strips and cAMP accumulation was measured in isolated ventricular cardiomyocytes from adult Wistar rats. Key results PTX amplified both the (R,R)- and (R,S)-fenoterol-evoked maximal inotropic response and concentration-dependent increases in cAMP accumulation. The EC50 values of fenoterol matched published binding affinities. The PTX enhancement of the Gs-selective (R,R)-fenoterol-mediated responses suggests that Gi regulates AC activity independent of receptor coupling to Gi protein. Consistent with this hypothesis, forskolin-evoked cAMP accumulation was increased and inotropic responses to forskolin were potentiated by PTX treatment. In non-PTX-treated tissue, phosphodiesterase (PDE) 3 and 4 inhibition or removal of either constitutive muscarinic receptor activation of Gi with atropine or removal of constitutive adenosine receptor activation with CGS 15943 had no effect upon contractility. However, in PTX-treated tissue, PDE3 and 4 inhibition alone increased basal levels of cAMP and accordingly evoked a large inotropic response. Conclusions and implications Together, these data indicate that Gi exerts intrinsic receptor-independent inhibitory activity upon AC. We propose that PTX treatment shifts the balance of intrinsic Gi and Gs activity upon AC towards Gs, enhancing the effect of all cAMP-mediated inotropic agents.

• Hussain, Rizwan; Aronsen, Jan Magnus; Afzal, Faraz; Sjaastad, Ivar; Osnes, Jan-Bjørn & Skomedal, Tor [Show all 8 contributors for this article] (2013). The functional activity of inhibitory G protein (Gi) is not increased in failing heart ventricle. Journal of Molecular and Cellular Cardiology. ISSN 0022-2828. 56, p. 129–138. doi: 10.1016/j.yjmcc.2012.11.015. Full text in Research Archive
• Levay, Magdolna; Krobert, Kurt Allen; Wittig, Karola; Voigt, Niels; Bermudez, Marcel & Wolber, Gerhard [Show all 9 contributors for this article] (2013). NSC23766, a widely used inhibitor of Rac1 activation, additionally acts as a competitive antagonist at muscarinic acetylcholine receptors. Journal of Pharmacology and Experimental Therapeutics. ISSN 0022-3565. 347(1), p. 69–79. doi: 10.1124/jpet.113.207266. Full text in Research Archive
• Molenaar, Peter; Christ, Torsten; Hussain, Rizwan; Engel, Andreas; Berk, Emanuel & Gillette, Katherine T. [Show all 12 contributors for this article] (2013). PDE3, but not PDE4, reduces beta 1- and beta 2-adrenoceptor-mediated inotropic and lusitropic effects in failing ventricle from metoprolol-treated patients. British Journal of Pharmacology. ISSN 0007-1188. 169(3), p. 528–538. doi: 10.1111/bph.12167. Full text in Research Archive
• Gravning, Jørgen A.; Ahmed, Muhammad Shakil; Qvigstad, Eirik; Krobert, Kurt Allen; Edvardsen, Thor & Moe, Ingvild Tronstad [Show all 13 contributors for this article] (2013). Connective Tissue Growth Factor/CCN2 Attenuates beta-Adrenergic Receptor Responsiveness and Cardiotoxicity by Induction of G Protein-Coupled Receptor Kinase-5 in Cardiomyocytes. Molecular Pharmacology. ISSN 0026-895X. 84(3), p. 372–383. doi: 10.1124/mol.113.087312. Full text in Research Archive
• Lueder, Thomas Gero von; Gravning, Jørgen A.; How, Ole-Jakob; Vinge, Leif Erik; Ahmed, Muhammad Shakil & Krobert, Kurt Allen [Show all 11 contributors for this article] (2012). Cardiomyocyte-restricted inhibition of G protein-coupled receptor kinase-3 attenuates cardiac dysfunction after chronic pressure overload. American Journal of Physiology. Heart and Circulatory Physiology. ISSN 0363-6135. 303(1), p. H66–H74. doi: 10.1152/ajpheart.00724.2011. Full text in Research Archive
• Riise, Jon; Ørstavik, Øivind; Qvigstad, Eirik; Dahl, Christen Peder; Osnes, Jan-Bjørn & Skomedal, Tor [Show all 8 contributors for this article] (2012). Prostaglandin E-1 facilitates inotropic effects of 5-HT4 serotonin receptors and beta-adrenoceptors in failing human heart. Basic Research in Cardiology. ISSN 0300-8428. 107(5). doi: 10.1007/s00395-012-0295-z. Full text in Research Archive
• Riise, Jon; Nguyen, Hong Cam Thi; Hussain, Rizwan; Dahl, Christen Peder; Ege, Maren Stapnes & Osnes, Jan-Bjørn [Show all 10 contributors for this article] (2012). Prostanoid-mediated inotropic responses are attenuated in failing human and rat ventricular myocardium. European Journal of Pharmacology. ISSN 0014-2999. 686(1-3), p. 66–73. doi: 10.1016/j.ejphar.2012.04.022. Full text in Research Archive
• Hussain, Rizwan; Afzal, Faraz; Mørk, Halvor Kjeang; Aronsen, Jan Magnus; Sjaastad, Ivar & Osnes, Jan-Bjørn [Show all 9 contributors for this article] (2011). Cyclic AMP-dependent inotropic effects are differentially regulated by muscarinic G(i)-dependent constitutive inhibition of adenylyl cyclase in failing rat ventricle. British Journal of Pharmacology. ISSN 0007-1188. 162(4), p. 908–916. doi: 10.1111/j.1476-5381.2010.01097.x. Full text in Research Archive
• Brudeli, Bjarne; Moltzau, Lise Roman; Andressen, Kjetil Wessel; Krobert, Kurt Allen; Klaveness, Jo & Levy, Finn Olav (2010). Synthesis and pharmacological properties of novel hydrophilic 5-HT4 receptor antagonists. Bioorganic & Medicinal Chemistry. ISSN 0968-0896. 18(24), p. 8600–8613. doi: 10.1016/j.bmc.2010.10.011. Full text in Research Archive
• Hussain, RI; Qvigstad, Eirik; Birkeland, Jon Arne; Eikemo, Hilde; Glende, A & Sjaastad, Ivar [Show all 10 contributors for this article] (2009). Activation of muscarinic receptors elicits inotropic responses in ventricular muscle from rats with heart failure through myosin light chain phosphorylation. British Journal of Pharmacology. ISSN 0007-1188. 156(4), p. 575–586. doi: 10.1111/j.1476-5381.2009.00016.x. Full text in Research Archive
• Hussain, Rizwan; Qvigstad, Erik; Birkeland, Jon Arne; Eikemo, Hilde; Glende, A & Sjaastad, Ivar [Show all 10 contributors for this article] (2009). Activation of muscarinic receptors elicits inotropic responses in ventricular muscle from rats with heart failure through myosin light chain phosphorylation. British Journal of Pharmacology. ISSN 0007-1188. 156(4), p. 575–586. doi: 10.1111/j.1750-3639.2009.00016.x. Full text in Research Archive Show summary

  Background and purpose: Muscarinic stimulation increases myofilament Ca2+ sensitivity with no apparent inotropic response in normal rat myocardium. Increased myofilament Ca2+ sensitivity is a molecular mechanism promoting increased contractility in failing cardiac tissue. Thus, muscarinic receptor activation could elicit inotropic responses in ventricular myocardium from rats with heart failure, through increasing phosphorylation of myosin light chain (MLC). Experimental approach: Contractile force was measured in left ventricular papillary muscles from male Wistar rats, 6 weeks after left coronary artery ligation or sham surgery. Muscles were also frozen, and MLC‐2 phosphorylation level was quantified. Key results: Carbachol (10 µmol·L−1) evoked a positive inotropic response only in muscles from rats with heart failure approximating 36% of that elicited by 1 µmol·L−1 isoproterenol (20 ± 1.5% and 56 ± 6.1% above basal respectively). Carbachol‐evoked inotropic responses did not correlate with infarction size but did correlate with increased left ventricular end diastolic pressure, heart weight/body weight ratio and lung weight, primary indicators of the severity of heart failure. Only muscarinic receptor antagonists selective for M2 receptors antagonized carbachol‐mediated inotropic effects with the expected potency. Carbachol‐evoked inotropic responses and increase in phosphorylated MLC‐2 were attenuated by MLC kinase (ML‐9) and Rho‐kinase inhibition (Y‐27632), and inotropic responses were abolished by Pertussis toxin pretreatment. Conclusion and implications: In failing ventricular muscle, muscarinic receptor activation, most likely via M2 receptors, provides inotropic support by increasing MLC phosphorylation and consequently, myofilament Ca2+ sensitivity. Enhancement of myofilament Ca2+ sensitivity, representing a less energy‐demanding mechanism of inotropic support may be particularly advantageous in failing hearts.

• Larsen, Karl-Otto; Lygren, Birgitte; Sjaastad, Ivar; Krobert, Kurt Allen; Arnkværn, Kristin & Florholmen, Geir [Show all 11 contributors for this article] (2008). Diastolic dysfunction in alveolar hypoxia: a role for interleukin-18-mediated increase in protein phosphatase 2A. Cardiovascular Research (CVR). ISSN 0008-6363. 80(1), p. 47–54. doi: 10.1093/cvr/cvn180. Full text in Research Archive
• Ramberg, Håkon; Eide, Turid; Krobert, Kurt Allen; Levy, Finn Olav; Dizeyi, N & Bjartell, AS [Show all 8 contributors for this article] (2008). Hormonal regulation of beta(2)-adrenergic receptor level in prostate cancer. The Prostate. ISSN 0270-4137. 68(10), p. 1133–1142. doi: 10.1002/pros.20778. Full text in Research Archive
• Levy, Finn Olav; Qvigstad, Eirik; Krobert, Kurt Allen; Skomedal, Tor & Osnes, Jan-Bjørn (2008). Effects of serotonin in failing cardiac ventricle: Signalling mechanisms and potential therapeutic implications. Neuropharmacology. ISSN 0028-3908. 55(6), p. 1066–1071. doi: 10.1016/j.neuropharm.2008.07.010. Full text in Research Archive
• Riise, J; Nguyen, Hong Cam Thi; Qvigstad, Eirik; Sandnes, Dagny Lise; Osnes, Jan-Bjørn & Skomedal, Tor [Show all 8 contributors for this article] (2008). Prostanoid F receptors elicit an inotropic effect in rat left ventricle by enhancing myosin light chain phosphorylation. Cardiovascular Research (CVR). ISSN 0008-6363. 80(3), p. 407–415. doi: 10.1093/cvr/cvn216. Full text in Research Archive
• Birkeland, Jon Arne; Sjaastad, Ivar; Brattelid, Trond; Qvigstad, Eirik; Moberg, Enrica Ratti & Krobert, Kurt Allen [Show all 11 contributors for this article] (2007). Effects of treatment with a 5-HT4 receptor antagonist in heart failure. British Journal of Pharmacology. ISSN 0007-1188. 150, p. 143–152. doi: 10.1038/sj.bjp.0706966. Full text in Research Archive
• Brattelid, Trond; Tveit, Kristine; Birkeland, Jon Arne; Sjaastad, Ivar; Qvigstad, Eirik & Krobert, Kurt Allen [Show all 10 contributors for this article] (2007). Expression of mRNA encoding G protein-coupled receptors involved in congestive heart failure : A quantitative RT-PCR study and the question of normalisation. Basic Research in Cardiology. ISSN 0300-8428. 102, p. 198–208. doi: 10.1007/s00395-007-0648-1. Full text in Research Archive
• Brattelid, Trond; Qvigstad, E; Birkeland, Jan Magne; Birkeland, Jon Arne; Swift, F & Bekkevold, SVS [Show all 12 contributors for this article] (2007). Serotonin responsiveness through 5-HT2A and 5-HT4 receptors is differentially regulated in hypertrophic and failing rat cardiac ventricle. Journal of Molecular and Cellular Cardiology. ISSN 0022-2828. 43, p. 767–779. doi: 10.1016/j.yjmcc.2007.08.019. Full text in Research Archive
• Andressen, Kjetil Wessel; Norum, Jens Henrik; Levy, Finn Olav & Krobert, Kurt Allen (2006). Activation of adenylyl cyclase by endogenous G(s)-coupled receptors in human embryonic kidney 293 cells is attenuated by 5-HT7 receptor expression. Molecular Pharmacology. ISSN 0026-895X. 69, p. 207–215. Full text in Research Archive
• Krobert, Kurt Allen; Andressen, Kjetil Wessel & Levy, Finn Olav (2006). Heterologous desensitization is evoked by both agonist and antagonist stimulation of the human 5-HT7 serotonin receptor. European Journal of Pharmacology. ISSN 0014-2999. 532, p. 1–10. Full text in Research Archive
• Larsen, Karl-Otto; Sjaastad, Ivar; Svindland, A; Krobert, Kurt Allen; Skjønsberg, Ole Henning & Christensen, Geir Arve (2006). Alveolar hypoxia induces left ventricular diastolic dysfunction and reduces phosphorylation of phospholamban in mice. American Journal of Physiology. Heart and Circulatory Physiology. ISSN 0363-6135. 291, p. H507–H516. Full text in Research Archive
• Qvigstad, Eirik; Sjaastad, Ivar; Brattelid, Trond; Nunn, Caroline; Swift, Fredrik & Birkeland, Jon Arne [Show all 12 contributors for this article] (2005). Dual serotonergic regulation of ventricular contractile force through 5-HT2A and 5-HT4 receptors induced in the acute failing heart. Circulation Research. ISSN 0009-7330. 97, p. 268–276. Full text in Research Archive
• Øie, Erik; Vinge, Leif Erik; Andersen, Geir Øystein; Yndestad, Arne; Krobert, Kurt Allen & Sandberg, Cecilie [Show all 11 contributors for this article] (2005). RAMP2 and RAMP3 rnRNA levels are increased in failing rat cardiomyocytes and associated with increased responsiveness to adrenomedullin. Journal of Molecular and Cellular Cardiology. ISSN 0022-2828. 38, p. 145–151. Full text in Research Archive
• Qvigstad, Eirik; Brattelid, Trond; Sjaastad, Ivar; Andressen, Kjetil Wessel; Krobert, Kurt Allen & Birkeland, Jon Arne [Show all 11 contributors for this article] (2005). Appearance of a ventricular 5-HT4 receptor-mediated inotropic response to serotonin in heart failure. Cardiovascular Research (CVR). ISSN 0008-6363. 65. Full text in Research Archive Show summary

  BACKGROUND: Current pharmacological treatment of congestive heart failure (CHF) addresses changes in neurohumoral stimulation or cardiac responsiveness to such stimulation. Yet, undiscovered neurohumoral changes, adaptive or maladaptive, may occur in CHF and suggest novel pharmacological treatment. Serotonin [5-hydroxytryptamine (5-HT)] enhances contractility and causes arrhythmias through 5-HT(4) receptors in human atrium and ventricle but not through rat ventricular 5-HT(4) receptors. OBJECTIVE: We investigated whether CHF could induce ventricular responsiveness to serotonin. METHODS: Postinfarction CHF was induced in male Wistar rats by coronary artery ligation. Contractility was measured in left ventricular papillary muscles 6 weeks after infarction. Messenger RNA was quantified by RT-PCR and cAMP by RIA. RESULTS: Serotonin caused positive inotropic (-logEC(50)=7.5) and lusitropic effects in CHF but not Sham papillary muscles. The inotropic effect of 10 muM serotonin in CHF (31.3+/-2.2%) was of similar size as the effect of 10 muM isoproterenol (34.0+/-1.7%). The effects of serotonin were antagonised by GR113808 (0.5-5 nM), consistent with mediation through 5-HT(4) receptors. This was further supported by positive inotropic effects of the 5-HT(4)-selective partial agonist RS67506. Carbachol blunted the serotonin responses and serotonin increased ventricular and cardiomyocyte cAMP, consistent with coupling to G(s) and adenylyl cyclase. Quantitative RT-PCR revealed fourfold increased 5-HT(4(b)) mRNA expression in CHF vs. Sham ventricles. CONCLUSION: Functional ventricular 5-HT(4) receptors are induced by myocardial infarction and CHF of the rat heart. We propose that they are a model for ventricular 5-HT(4) receptors of human failing heart and may play a pathophysiological role in heart failure.

• Qvigstad, Eirik; Brattelid, Trond; Sjaastad, Ivar; Molenaar, P.; Birkeland, Jon Arne & Andressen, Kjetil Wessel [Show all 12 contributors for this article] (2005). Rationale for treatment of heart failure by blockade of ventricular serotonin receptors appearing in heart failure, Proceedings of the 25th European Section Meeting, International Society for Heart Research, Tromsø, Norway, June 21-25, 2005. Medimond. ISSN 9788875871642. p. 7–12. Full text in Research Archive Show summary

  Serotonin (5-hydroxytryptamine, 5-HT) enhances contractility and causes arrhythmias through human atrial 5-HT4 receptors. We recently found that porcine and human as well as failing rat cardiac ventricle also responds to serotonin through 5-HT4 receptors which, like beta-adrenoceptors, are coupled via the Gs protein to increased cAMP formation. In rats with 6-week post-infarction congestive heart failure (CHF), the maximal inotropic effect of serotonin was comparable in size with that of isoproterenol. Given the similar signalling systems utilised by the two receptors and that blockade of beta-adrenoceptors is beneficial in CHF, we propose that blockade of 5-HT4 receptors may also be beneficial in CHF.

• Krobert, Kurt Allen; Brattelid, Trond; Levy, Finn Olav & Kaumann, Alberto Julio (2005). Prucalopride is a partial agonist through human and porcine atrial 5-HT4 receptors: comparison with recombinant human 5-HT4 splice variants. Naunyn-Schmiedeberg's Archives of Pharmacology. ISSN 0028-1298. 371(6), p. 471–479. Full text in Research Archive Show summary

  Prucalopride is a gastrointestinal prokinetic drug that acts through 5-HT4 receptors, but its potential effects on cardiac atrial function are unknown. We investigated the effects of prucalopride on human right atrium, piglet left atrium, and piglet sinoatrial node. The effects of prucalopride on 5-HT4 receptor splice variants a, b, g and i, known to be expressed in human atrium, were studied for comparison. Prucalopride was an inotropic partial agonist, compared with 5-HT, on paced human atrial trabeculae (-logEC50M=7.4) and porcine left atria (-logEC50M=7.2), with intrinsic activity of 0.77 and 0.63 respectively. Prucalopride (1 microM) surmountably antagonized the positive inotropic effects of 5-HT on human (pK(P)=7.2) and porcine (pK(P)=7.1) atrium. Prucalopride was also a chronotropic partial agonist (-logEC50M=7.4, intrinsic activity=0.72 with respect to 5-HT) on spontaneously beating piglet atria. The cardiostimulant effects of prucalopride were prevented by GR113808 (1 microM), consistent with mediation through 5-HT4 receptors. Prucalopride bound to recombinant 5-HT4(a), 5-HT4(b), 5-HT4(g), and 5-HT4(i) receptors, labeled by [3H]GR113808, with pKi values of 7.6, 7.5, 7.4, and 7.8 respectively. Prucalopride stimulated adenylyl cyclase as a partial agonist on 5-HT4(a), 5-HT4(b), and 5-HT4(i) receptors with intrinsic activities of 0.82, 0.86, and 0.78 and -logEC50 values of 7.2, 7.3, and 7.2 respectively. At the 5-HT4(g) receptor prucalopride acted as a full agonist (-logEC50M=8.0) compared with 5-HT in the cell line tested, which was probably due to high receptor expression levels. We conclude that prucalopride is a cardiostimulatory partial agonist through human and porcine 5-HT4 receptors. Since prucalopride acts similarly through 5-HT4(a), 5-HT4(b), 5-HT4(g), and 5-HT4(i) receptors, any of these variants could be involved in the mediation of cardiostimulation.

• Brattelid, Trond; Kvingedal, Ane Marit; Krobert, Kurt Allen; Andressen, Kjetil Wessel; Bach, Trond & Hystad, Marit Elise [Show all 8 contributors for this article] (2004). Cloning, pharmacological characterisation and tissue distribution of a novel 5-HT4 receptor splice variant, 5-HT4(i). Naunyn-Schmiedeberg's Archives of Pharmacology. ISSN 0028-1298. 369(6), p. 616–628. Full text in Research Archive Show summary

  5-HT4 receptor pre-mRNA is alternatively spliced in human (h) tissue to produce several splice variants, called 5-HT4(a) to 5-HT4(h) and 5-HT4(n). Polymerase chain reaction (PCR) with primers designed to amplify both 5-HT4(a) and 5-HT4(b) amplified three additional bands in different tissues, two representing different mRNA species both encoding 5-HT4(g) and one representing mRNA for a novel splice variant named 5-HT4(i), cloned from testis and pancreas respectively. Primary and nested PCR detected both 5-HT4(g) and 5-HT4(i) in multiple tissues. Whereas 5-HT4(i), was found in all cardiovascular tissues analysed, 5-HT4(g) was mainly present in atria. However, quantitative RT-PCR indicated 5-HT4(g) expression also in cardiac ventricle. The pharmacological profiles and ability to activate adenylyl cyclase (AC) were compared between four recombinant h5-HT4 splice variants (a, b, g and i) expressed transiently and stably in HEK293 cells. Displacement of [(3)H]GR113808 with ten ligands revealed identical pharmacological profiles (affinity rank order: GR125487, SB207710, GR113808>SB203186>serotonin, cisapride, tropisetron>renzapride, 5-MeOT>5-CT). In transiently transfected HEK293 cells cisapride was a partial agonist compared to serotonin at 5-HT4(b), 5-HT4(g) and 5-HT4(i) receptors. In membranes from HEK293 cells stably expressing 5-HT4(g) (3,000 fmol/mg protein) or 5-HT4(i) (500 fmol/mg protein), serotonin and 5-MeOT were full agonists while cisapride was full agonist at 5-HT4(g) and partial agonist at 5-HT4(i), probably due to different receptor expression levels. At both 5-HT4(g) and 5-HT4(i), the behaviour of 5-HT4 receptor antagonists was dependent on receptor level. At high receptor levels, tropisetron and SB207710 and to a variable extent SB203186 and GR113808 displayed some partial agonist activity, whereas GR125487 and SB207266 reduced the AC activity below basal, indicating both receptors to be constitutively active. We conclude that the novel 5-HT4(i) receptor splice variant is pharmacologically indistinguishable from other 5-HT4 splice variants and that the 5-HT4(i) C-terminal tail does not influence coupling to AC.

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• Melsom, CB; Hussain, Rizwan; Aronsen, Jan Magnus; Sjaastad, Ivar; Osnes, Jan-Bjørn & Skomedal, Tor [Show all 8 contributors for this article] (2011). The role of inhibitory G protein upon beta-adrenoceptor-mediated signalling and inotropic responses in normal and failing rat heart left ventricle: Functional evidence of "tonic" Gi activation. Full text in Research Archive
• Gravning, Jørgen A.; Ahmed, Muhammad Shakil; Qvigstad, Eirik; Sagave, Julia Fritzi; Krobert, Kurt Allen & Edvardsen, Thor [Show all 10 contributors for this article] (2009). CCN2/CTGF - Connective Tissue Growth Factor - Reduces beta-Adrenergic Receptor Responsiveness and Catecholamine-Induced Cardiotoxicity by Upregulation of Cardiac Myocyte G Protein-Coupled Receptor Kinase-5. Circulation. ISSN 0009-7322. 120(18), p. S720–S720. Full text in Research Archive
• Larsen, Karl-Otto; Lygren, Birgitte; Sjaastad, Ivar; Krobert, Kurt Allen; Arnkværn, Kristin & Florholmen, Geir [Show all 10 contributors for this article] (2009). Mechanisms for cardiac dysfunction in COPD and respiratory failure. Respiratory Medicine. ISSN 0954-6111. 103, p. S6–S7. Full text in Research Archive
• Larsen, Karl-Otto; Lygren, Birgitte; Sjaastad, Ivar; Krobert, Kurt Allen; Arnkværn, Kristin & Florholmen, Geir [Show all 11 contributors for this article] (2009). Increased circulating IL-18; a possible mechanism for hypoxia-induced cardiac dysfunction. Full text in Research Archive
• Krobert, Kurt Allen; Hussain, Rizwan; Afzal, Faraz; Aronsen, Jon magnus; Sjaastad, Ivar & Osnes, Jan-Bjørn [Show all 8 contributors for this article] (2009). Inreased Gi activity does not contribute to the reduced beta-adrenergic inotropic effect in failing rat ventricle but Gi acts as a tonic brake on basal adenylyl cyclase activity. Full text in Research Archive
• Gravning, Jørgen Amundsen; Ahmed, Muhammad Shakil; Qvigstad, Erik; Sagave, Julia Fritzi; Krobert, Kurt Allen & Edvardsen, Thor [Show all 10 contributors for this article] (2008). Connective tissue growth factor (CTGF/CCN2) desensitizes myocardial beta-adrenergic receptor signaling and inhibits isoproterenol induced hypertrophy. Full text in Research Archive
• Larsen, Karl-Otto; Lygren, Birgitte; Sjaastad, Ivar; Krobert, Kurt Allen; Florholmen, Geir & Arnkværn, Kristin [Show all 10 contributors for this article] (2008). Alveolar hypoxia induces cardiac diastolic dysfunction: a role for a reduction in the calcium regulating protein phospholamban induced by IL-18. Full text in Research Archive
• Larsen, Karl-Otto; Lygren, Birgitte; Sjaastad, Ivar; Krobert, Kurt Allen; Arnkværn, Kristin & Florholmen, Geir [Show all 10 contributors for this article] (2008). Mechanisms for cardiac dysfunction in COPD and respiratory failure. Full text in Research Archive
• Larsen, Karl-Otto; Lygren, Birgitte; Sjaastad, Ivar; Krobert, Kurt Allen; Florholmen, Geir & Arnkværn, Kristin [Show all 10 contributors for this article] (2007). Diastolic dysfunction in alveolar hypoxia: A role for interleukin-18 induced increase in protein phosphatase 2A and reduction in phospholamban phosphorylation. Full text in Research Archive
• Krobert, Kurt Allen; Hussain, Rizwan; Mørk, Halvor Kjeang; Qvigstad, Eirik; Sjaastad, Ivar & Osnes, Jan-Bjørn [Show all 8 contributors for this article] (2007). cAMP-dependent inotropic effects are differentially regulated by muscarinic inhibition in failing rat ventricle. Journal of Molecular and Cellular Cardiology. ISSN 0022-2828. 42(6), p. S35–S35. Full text in Research Archive
• Larsen, Karl-Otto; Lygren, Birgitte; Sjaastad, Ivar; Krobert, Kurt Allen; Florholmen, Geir & Arnkværn, Kristin [Show all 10 contributors for this article] (2007). Increased PP1 and PP2A mediating reduced Ser16 phosphorylated PLB is a possible mechanism for cardiac dysfunction in alveolar hypoxia. Journal of Molecular and Cellular Cardiology. ISSN 0022-2828. 42(6), p. S245–S245. Full text in Research Archive
• Larsen, Karl-Otto; Lygren, Birgitte; Sjaastad, Ivar; Krobert, Kurt Allen; Florholmen, Geir & Arnkværn, Kristin [Show all 10 contributors for this article] (2007). Alveolar hypoxia induces cardiac dysfunction, possibly mediated through increased amounts of phosphatases, leading to dephosphorylation of calcium regulatory proteins. Full text in Research Archive
• Larsen, Karl-Otto; Lygren, Birgitte; Sjaastad, Ivar; Krobert, Kurt Allen; Florholmen, Geir & Arnkværn, Kristin [Show all 10 contributors for this article] (2007). Hypoxia induced cardiac dysfunction maybe caused by increased IL-18 levels leading to dephosphorylation of Ca2+ handling proteins. Full text in Research Archive
• Brattelid, Trond; Qvigstad, Eirik; Birkeland, Jon Arne; Swift, Fredrik; Bekkevold, SVS & Krobert, Kurt Allen [Show all 11 contributors for this article] (2006). Serotonin responsiveness through 5-HT2A and 5-HT4 receptors is differentially regulated in hypertrophic and failing rat cardiac ventricle. Journal of Molecular and Cellular Cardiology. ISSN 0022-2828. 40, p. 944–945. Full text in Research Archive
• Qvigstad, Eirik; Sjaastad, Ivar; Brattelid, Trond; Nunn, Caroline; Swift, Fredrik & Birkeland, Jon Arne [Show all 12 contributors for this article] (2006). Induction of functional serotonin 5-HT2A and 5-HT4 receptors in the acute failing cardiac ventricle. Journal of Pharmacological Sciences (JPS). ISSN 1347-8613. 101, p. 73–73. Full text in Research Archive
• Andressen, Kjetil Wessel; Norum, Jens Henrik; Levy, Finn Olav & Krobert, Kurt Allen (2006). Activation of adenylyl cyclase in HEK293 cells by endogenous G(s)-coupled receptors is attenuated by 5-HT7 receptor expression. Journal of Pharmacological Sciences (JPS). ISSN 1347-8613. 101, p. 128–128. Full text in Research Archive
• Birkeland, Jon Arne; Sjaastad, Ivar; Brattelid, Trond; Qvigstad, Eirik; Moberg, Enrica Ratti & Krobert, Kurt Allen [Show all 11 contributors for this article] (2006). Treatment with a 5-HT4 serotonin receptor antagonist improves function of the failing heart. Journal of Pharmacological Sciences (JPS). ISSN 1347-8613. 101, p. 75–75. Full text in Research Archive
• Birkeland, Jon Arne; Sjaastad, Ivar; Brattelid, Trond; Qvigstad, Eirik; Moberg, Enrica Ratti & Krobert, Kurt Allen [Show all 11 contributors for this article] (2006). Treatment with a 5-HT4 serotonin receptor antagonist improves function of the failing heart. Journal of Molecular and Cellular Cardiology. ISSN 0022-2828. 40, p. 943–944. Full text in Research Archive
• Eikemo, Hilde; Qvigstad, Eirik; Krobert, Kurt Allen; Nunn, Caroline; Levy, Finn Olav & Skomedal, Tor [Show all 7 contributors for this article] (2006). Kinetics of myosin light chain phosphorylation in the heart. Journal of Molecular and Cellular Cardiology. ISSN 0022-2828. 40, p. 994–995. Full text in Research Archive
• Brattelid, Trond; Qvigstad, Eirik; Birkeland, Jon Arne; Swift, Fredrik; Bekkevold, Silje Veslemøy & Krobert, Kurt Allen [Show all 11 contributors for this article] (2006). Serotonin responsiveness through 5-HT2A and 5-HT4 receptors is differentially regulated in hypertrophic and failing rat cardiac ventricle. Journal of Pharmacological Sciences (JPS). ISSN 1347-8613. 101, p. 74–74. Full text in Research Archive
• Birkeland, Jon Arne; Qvigstad, Eirik; Sjaastad, Ivar; Brattelid, Trond; Krobert, Kurt Allen & Sejersted, Ole M [Show all 11 contributors for this article] (2005). Induction of a 5-HT4 receptor-mediated inotropic response to serotonin in failing ventricular cardiomyocytes. Biophysical Journal. ISSN 0006-3495. 88. Full text in Research Archive
• Qvigstad, Eirik; Birkeland, Jon Arne; Sjaastad, Ivar; Brattelid, Trond; Andressen, Kjetil Wessel & Krobert, Kurt Allen [Show all 12 contributors for this article] (2005). Treatment of heart failure by blockade of ventricular myocardial serotonin receptors appearing in heart failure. Journal of Molecular and Cellular Cardiology. ISSN 0022-2828. 38, p. 1041–1041. Full text in Research Archive

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