Exchanges of sodium ions in the central nervous system of Anodonta cygnea.

Abstract

ABSTRACT The concentrations of sodium and potassium ions have been measured in the blood and tissues of the cerebro-visceral connective of the freshwater mussel Anodonta. It is shown that, despite the relatively low concentration of sodium ions in the blood, a concentration gradient of this cation is maintained between the extracellular fluid and the nerve cells because of the extremely low intracellular concentration of this cation. Experiments using 24Na and 22Na have shown that there is relatively rapid exchange of sodium ions between the blood and the central nervous tissues. The efflux of labelled sodium occurred as a two-stage process, in which an initial fast fraction gives way to a slower exponential decline. The results can be accounted for on the assumption that efflux of sodium ions in the fast fraction, at o° C., represents the cations contained in the extracellular fluid. This assumption implies that there is little regulation of the over-all concentration of sodium ions in the extracellular fluid. The results are discussed in relation to the available evidence on the structure and electrophysiology of the cerebro-visceral connectives.