Volume regulation of frog skin epithelium

Previous results (MacRobbie & Ussing 1961) in combination with published values for cellular chloride concentration and for intracellular potentials show that the chloride concentration in frog skin epithelium cells is higher than predicted for equilibrium with the inside bathing solution. Both the apical and the basolateral membrane of these cells are normally almost tight to chloride, so that the maintenance of the high chloride concentration requires little work. A basolateral permeability to chloride is, however, activated by cell swelling, and the cells lose KCl. It is now shown that the KCl thus lost cannot be regained neither in the absence of sodium in the inside bath nor in the presence of furosemide. The volume regulation reactions are, however, independent of the composition of the outside bath. It is concluded that the recovery of KCl by the epithelium is due to a basolateral co-transport of NaCl from medium to cells, combined with return of Na to the medium via the Na-K pump. The co-transport mechanism thus restores the high chloride concentration of the cells, but seems to be virtually dormant unless the cells have lost chloride.