The goals of this project are to elucidate the mechanisms of neurohormonal control of cellular volume regulation in marine bivalve molluscs. Two neural products, the peptide FMRFamide and the transmitter 5-hydroxytryptamine (5HT) increase the efflux of amino acids from isolated ventricles of the clam Mercenaria mercenaria exposed to hypoosmotic stress. Phorbol esters also potentiate the amino acid efflux of tissues in hypoosmotic media, suggesting that the activation of protein kinase C is involved in the control of hypoosmotic volume regulation. The roles of changes in intracellular Ca++ levels in the modulation of the amino acid efflux of tissues in hypoosmotic media will be investigated. Changes in the activity of protein kinase C in tissues exposed to hypoosmotic media will be determined. The possibility that neurosecretory cells in the visceral ganglion release FMRFamide into the circulation in response to decreases in ambient salinity will also be investigated using immunocytochemical techniques. While neurohormones have been implicatead in the control of salt and water balance in invertebrates, no known hormone has yet been clearly associated with the control of a specific osmoregulatory mechanism. This project will associate the neurosecretion of FMRFamide with the control of hypoosmotic cellular volume regulation in molluscs. In addition, this project will provide new information on the cellular mechanisms involved in volume regulation in molluscs and other animals.
