The effects of FMRFamide, 5-hydroxytryptamine and phorbol esters on the heart of the mussel Geukensia demissa.
The ventricle of the mussel Geukensia demissa is inhibited by 5-hydroxytryptamine and excited by the molluscan neuropeptide FMRFamide. Supra-threshold doses of amide result in marked positive chronotropy and inotropy within 5-15 s. 5-Hydroxytryptamine at 10(-8) M produces diastolic arrest within 10 s. A 1-min exposure to FMRFamide (5 x 10(-8) M) results in a small increase in the cytoplasmic levels of adenosine 3',5'-cyclic monophosphate; shorter or longer exposures have no effect. The cAMP content of ventricles incubated in 5 x 10(-8) M 5-hydroxytryptamine for 1 min decreases by 2.3 pmol/mg protein; longer or shorter incubations have no effect. Treatment with forskolin results in 3- or 4-fold increases in adenosine 3',5'-cyclic monophosphate, but forskolin has no effect on the mechanical activity of the ventricle. The levels of inositol monophosphate, inositol 1,4-diphosphate, and inositol 1,4,5-triphosphate in tissues exposed to 5-hydroxytryptamine are not different from levels in control tissues. FMRFamide decreases the levels of these phosphoinositides by 50% or more. Lower concentrations of phorbol 12,13-diacetate (10(-8) to 10(-7) M) and phorbol 12-myristate,13-acetate (10(-6) M) cause positive chronotropy in the isolated ventricle; higher concentrations induce systolic arrest. These results suggest that the effects of 5HT on the ventricle are not mediated by adenosine 3',5'-cyclic monophosphate or inositol 1,4,5-triphosphate. The effects of FMRFamide may involve a decrease in inositol 1,4,5-triphosphate. The effects of amide may involve a decrease in inositol 1,4,5-triphosphate. The response of the ventricles to phorbol esters suggest that protein kinase C may be involved in the regulation of cardiac contractility.
Biology Department, University of Southwestern Louisiana, Lafayette 70504.
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Bayakly
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Deaton
D000818:Animals; D049872:Bivalvia / Q000502:physiology*; D000242:Cyclic AMP / Q000378:metabolism; D019835:FMRFamide; D006321:Heart / Q000187:drug effects* / Q000502:physiology; D006339:Heart Rate / Q000187:drug effects; D007295:Inositol Phosphates / Q000378:metabolism; D009200:Myocardial Contraction / Q000187:drug effects; D009206:Myocardium / Q000378:metabolism; D009479:Neuropeptides / Q000494:pharmacology*; D018377:Neurotransmitter Agents / Q000494:pharmacology; D010703:Phorbol Esters / Q000494:pharmacology; D012701:Serotonin / Q000494:pharmacology; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology
D007295:Inositol Phosphates; D009479:Neuropeptides; D018377:Neurotransmitter Agents; D010703:Phorbol Esters; C008874:phorbol-12,13-diacetate; D012701:Serotonin; D019835:FMRFamide; D000242:Cyclic AMP; D013755:Tetradecanoylphorbol Acetate