Volume regulation of frog skin epithelium

Abstract

Previous results (MacRobbie and Ussing) in combination with published values for cellular Cl concentration and for intracellular potentials showed that the Cl 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 Cl, so that the maintenance of the high Cl concentration requires little work. A basolateral permeability to Cl is, however, activated by cell swelling, and the cells lose KCl. The KCl thus lost cannot be regained neither in the absence of Na in the inside bath nor in the presence of furosemide. The volume regulation reactions are, however, independent of the composition of the outside bath. 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 Cl concentration of the cells, but seems to be virtually dormant unless the cells have lost Cl.