The regulation of volume and ion composition in frog skin.

1. Chemical determinations of Cl- in frog skin indicate that the intracellular concentration of this ion is above that corresponding to an equilibrium distribution. 2. Published data on Na+ efflux from the cell compartments into the two external bathing solutions, and on unidirectional fluxes across the whole preparation suggest that there are large unidirectional fluxes across the basolateral membranes. 3. Cl- uptake from the mucosal barrier is very small, and the removal of Cl- from the mucosal bathing solution does not affect the intracellular Cl- concentration. 4. Removal of Cl- from the serosal bathing solution produces a drastic decrease in cell Cl- together with a loss of water. 5. This is accompanied by a less marked effect on Na+ and K+ content of the cells. 6. The removal of Na+ from the serosal bathing solution produces also a decrease in Cl-, Na+ and K+ content of the cells with a marked loss of water. 7. It is suggested that the basolateral membrane of the frog skin is the site of mechanisms able to regulate volume and ion composition of the epithelial cells and that part of these mechanisms consists of a coupling between the movements of Na+ and Cl-.