Electrophysiology of chloride transport in Aplysia (mollusk) intestine.

This investigation was principally undertaken to examine the mechanism of Cl- transport across the Aplysia californica intestinal epithelium. Previous results have shown: 1) the transmural potential difference (psi m leads to s) and the mucosal membrane potential difference (psi m) to be negative relative to the mucosal solution, 2) mucosal D-glucose hyperpolarized psi m leads to s and depolarized psi m, 3) mucosal D-glucose significantly increased intracellular Cl- activity (aiCl), however the electrochemical potential (-mu i) for intracellular Cl- was significantly less in both cases, than the -muCl in the mucosal solution, 4) replacing Cl- in the bathing medium with SO-4(2) significantly reduced both psi m and psi m leads to s, and 5) the energy within the electrochemical potential difference for Na+ (delta -mu Na) directed from mucosa to cytosol was energetically adequate so that intracellular Cl- accumulation could occur. New results showed: 1) psi m and psi m leads to s to significantly hyperpolarize when Na+ was replaced with Tris+ in the bathing medium, 2) aiCl decreased from 13.9 +/- 0.5 to 9.1 +/- 0.3 mM when Na+ was replaced with Tris+ in the bathing medium. The intracellular -muCl, both in the presence and absence of Na+, was significantly less than -muCl in the mucosal medium. These results suggest that Na+ and Cl- transport across the mucosal membrane are not mechanistically coupled and that an active extrusion mechanism for Cl- exists in the lateral-serosal membrane of the surface epithelial cells of A. californica intestine.