[Ionic composition of mollusk cells--evolutionary and ecologic aspects]

Abstract

Marine molluscs exhibit relative constancy in intracellular potassium at the back ground of significant changes in intracellular sodium during acclimation to differen salinities. These changes, which were observed in cells of the adductor muscle and hepa topancreas, result mainly from active extrusion of sodium (possibly, of chloride as well) from the cell at low salinities and accumulation of these ions within the cell during the increase in salinity. Changes in intracellular concentration of sodium and chloride ions serve presumably as one of the main mechanisms of volume stabilization of cells, which together with the amino acid regulation alleviates the hydration of cells at different salinities. The capacity of cells to keep their potassium accounts for the maintenance of Ki/Ko ratio during changes in cellular volume induced by osmotic effects. These data are discussed in relation to two alternative hypotheses of the decreased and close to the present salinity of ocean at the initial stages of formation of the ionic composition of cells.