A SURVEY OF THE RESPONSES OF BIVALVE HEARTS TO THE MOLLUSCAN NEUROPEPTIDE FMRFAMIDE AND TO 5-HYDROXYTRYPTAMINE

Abstract

Ventricles from 50 species of bivalved molluscs were surveyed for their mechanical responses to the molluscan neuropeptide FMRFamide (Phe-Met-Arg-Phe-NH2 and to 5-hydroxytryptamine (5HT). Both were predominantly cardioexcitatory, but neither was exclusively so. FMRFamide was inhibitory or weakly excitatory more often than 5HT, and such effects were most common in the subclasses Paleoheterodonta and Heterodonta. In contrast, 5HT was only rarely inhibitory or even weakly excitatory, and such effects were most common in the subclass Pteriomorphia. The responses to FMRFamide or 5HT were strikingly uniform in some bivalve families, but characteristically diverse in others. Thus, FMRFamide is neither a general cardioexcitor nor a general serotonomimetic agent.