Meeting Abstract
Recent reports suggest that octopamine, a biogenic amine that is ubiquitous in arthropods, is a cardioexcitatory agent in the blue mussel, Mytilus edulis. To investigate the effects of octopamine on bivalve hearts, we isolated ventricles from Guekensia demissa and Mercenaria mercenaria and suspended the preparations in organ baths. The mechanical activity of the isolated ventricles was monitored with force transducers (Grass FT 03) and an ink-writing oscillograph (Grass 7). The ventricles were challenged with doses of octopamine, dopamine, histidine, epinephrine, and serotonin. Octopamine had mixed effects on ventricles of both species. Dopamine was cardioexcitatory at concentrations. Histamine and epinephrine increased the amplitude of contraction. Serotonin inhibited G. demissa ventricles. The results of these experiments with epinephrine and dopamine are largely consistent with published data on the isolated ventricles of a number of other bivalves. In most species, the heart is excited by both of these agents, albeit at high concentrations. Serotonin is cardioexcitatory in most species, but can be inhibitory (as in the ventricles from Louisiana populations of G. demissa) in some species. The effects of octopamine and histidine on the hearts of bivalves have not been extensively studied. The key question is: what is the nature of biogenic amine receptors in bivalve ventricles? Are there receptors for all of these neuroeffectors, or are the effects reported due to cross-talk?
