5-Hydroxytryptamine induces phospholipase C-mediated hydrolysis of phosphoinositides through 5-hydroxytryptamine-2 receptors in cultured fetal mouse ventricular myocytes.
5-Hydroxytryptamine (5-HT) stimulates the rate and force of cardiac contraction. However, the molecular mechanisms of 5-HT actions on the heart are unknown. We examined effects of 5-HT on phospholipase C-mediated hydrolysis of phosphoinositides and its regulation in cultured fetal mouse ventricular myocytes labeled with [3H]inositol. Accumulation of inositol monophosphate, inositol bisphosphate, and inositol trisphosphate was assessed after stimulation with 5-HT, catecholamines, and AlF4-. Inositol bisphosphate and trisphosphate reached a peak at 15 minutes by 5-HT stimulation and at 30 minutes by AlF4- stimulation. Inositol monophosphate accumulated linearly for at least 30 minutes in the presence of LiCl. The 5-HT effect was dose dependent, and the threshold concentration was 0.1 microM with the half-maximum effective concentration of 1 microM. Ketanserin in nanomolar concentrations inhibited the phospholipase C reaction by 100 microM 5-HT with the half-maximum inhibitory concentration of 0.5 nM. Pertussis toxin (100-1,000 ng/ml) did not influence the phospholipase C reaction by 5-HT, but it partially inhibited the reaction by AlF4-. Protein kinase C-activating phorbol esters like 12-O-tetradecanoylphorbol 13-acetate (TPA) and phorbol 12,13-dibutyrate, but not 4 alpha-phorbol 12,13-didecanoate, which is inactive for protein kinase C, completely inhibited the reaction by 5-HT; TPA showed 30% inhibition on the reaction by AlF4-. The magnitude of accumulated inositol phosphates by AlF4- was at least several times greater than that by 5-HT. Norepinephrine- and epinephrine-stimulated phospholipase C reactions were completely abolished by prazosin. These results suggest that 5-HT directly stimulates phospholipase C-mediated hydrolysis of phosphoinositides through 5-hydroxytryptamine-2 (5-HT2) receptors in the ventricular myocytes and that this reaction is negatively regulated by protein kinase C. 5-HT2 receptors may be coupled to phospholipase C via a pertussis toxin-insensitive GTP-binding protein in the myocytes.
Hamamori
Y
Y
First Department of Internal Medicine, Kobe University School of Medicine, Japan.
Yokoyama
M
M
Yamada
M
M
Akita
H
H
Goshima
K
K
Fukuzaki
H
H
D000535:Aluminum / Q000494:pharmacology; D000077410:Aluminum Chloride; D017607:Aluminum Compounds; D000818:Animals; D002478:Cells, Cultured; D002712:Chlorides / Q000494:pharmacology; D005333:Fetus / Q000378:metabolism; D006868:Hydrolysis; D007295:Inositol Phosphates / Q000037:antagonists & inhibitors / Q000378:metabolism; D007650:Ketanserin / Q000494:pharmacology; D051379:Mice / Q000196:embryology; D009206:Myocardium / Q000166:cytology / Q000378:metabolism*; D037342:Pertussis Toxin; D010703:Phorbol Esters / Q000494:pharmacology; D010716:Phosphatidylinositols / Q000378:metabolism*; D011224:Prazosin / Q000494:pharmacology; D011985:Receptors, Serotonin / Q000378:metabolism*; D012701:Serotonin / Q000494:pharmacology*; D012969:Sodium Fluoride / Q000494:pharmacology; D010738:Type C Phospholipases / Q000502:physiology*; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
D017607:Aluminum Compounds; D002712:Chlorides; D007295:Inositol Phosphates; D010703:Phorbol Esters; D010716:Phosphatidylinositols; D011985:Receptors, Serotonin; D010566:Virulence Factors, Bordetella; D012701:Serotonin; D000077410:Aluminum Chloride; D012969:Sodium Fluoride; D007650:Ketanserin; D000535:Aluminum; D037342:Pertussis Toxin; D010738:Type C Phospholipases; D011224:Prazosin