Phosphorylation of phospholamban and troponin I through 5-HT4 receptors in the isolated human atrium.
We studied the mRNA expression and function of 5-hydroxytryptamine (5-HT) receptors as well as their signal transduction in right atrial tissue from patients undergoing cardiac surgery and right ventricular tissue from human donor hearts. In isolated, electrically driven strips from human right atrium, 5-HT exerted concentration-dependent positive inotropic effects (EC(50) value = 0.10 +/- 0.01 microM) and hastened relaxation (positive lusitropic effect). The 5-HT(4) receptor antagonists SB203186 or GR125487 antagonised these effects. 5-HT (2 microM) increased the content of cyclic adenosine monophosphate (cAMP) from 6.86 +/- 1.36 to 19.1 +/- 2.45 pmol/mg protein (n = 6, p < 0.05) but did not alter the tissue content of inositol-1,4,5-trisphosphate (IP(3)). With reverse transcription polymerase chain reaction, mRNAs coding for the 5-HT(4) receptor splice variants 5-HT(4(a)), 5-HT(4(b)) and 5-HT(4(c)) were detected in human right atrium and right ventricle. 5-HT(2A) mRNA only was measurable in human atrium. Expression level of total 5-HT(4) receptor mRNA in the right ventricle amounted to 41% (n = 5-8) of that in the right atrium. 5-HT (2 microM) increased the atrial phosphorylation states of phospholamban to 168% at serine-16 and to 150% at threonine-17 (n = 4; p < 0.05) and of the inhibitory subunit of troponin to 150% (n = 6; p < 0.05). In conclusion, the positive inotropic and lusitropic effects of 5-HT in electrically driven human right atria are mediated via 5-HT(4) receptors. These effects are accompanied by and probably due to an increase in cAMP content and the subsequent elevation of the phosphorylation state of Ca(2+) regulatory proteins.
Gergs
Ulrich
U
Institut für Pharmakologie und Toxikologie, Medizinische Fakultät, Martin-Luther-Universität Halle-Wittenberg, Magdeburger Str. 4, 06112, Halle, Germany. ulrich.gergs@medizin.uni-halle.de
Neumann
Joachim
J
Simm
Andreas
A
Silber
Rolf-Edgar
RE
Remmers
Freerk Ole
FO
Läer
Stephanie
S
D000368:Aged; D000375:Aging / Q000502:physiology; D016275:Atrial Function / Q000187:drug effects; D002135:Calcium-Binding Proteins / Q000378:metabolism*; D000242:Cyclic AMP / Q000378:metabolism; D004558:Electric Stimulation; D005260:Female; D015870:Gene Expression / Q000235:genetics; D006325:Heart Atria / Q000187:drug effects / Q000378:metabolism*; D006352:Heart Ventricles / Q000378:metabolism; D006801:Humans; D066298:In Vitro Techniques; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism; D007545:Isoproterenol / Q000494:pharmacology; D008297:Male; D008875:Middle Aged; D009200:Myocardial Contraction / Q000187:drug effects; D010766:Phosphorylation / Q000187:drug effects; D020033:Protein Isoforms / Q000235:genetics; D044402:Receptor, Serotonin, 5-HT2A / Q000235:genetics; D044422:Receptors, Serotonin, 5-HT4 / Q000502:physiology*; D012701:Serotonin / Q000494:pharmacology; D058832:Serotonin 5-HT4 Receptor Antagonists; D012702:Serotonin Antagonists / Q000494:pharmacology; D013268:Stimulation, Chemical; D019210:Troponin I / Q000378:metabolism*; D000099211:Phospholamban
D002135:Calcium-Binding Proteins; D000242:Cyclic AMP; D015544:Inositol 1,4,5-Trisphosphate; D007545:Isoproterenol; D020033:Protein Isoforms; D044402:Receptor, Serotonin, 5-HT2A; D044422:Receptors, Serotonin, 5-HT4; D012701:Serotonin; D058832:Serotonin 5-HT4 Receptor Antagonists; D012702:Serotonin Antagonists; D019210:Troponin I; D000099211:Phospholamban