Pumped movements of sodium and potassium ions in the isolated epithelium of the frog skin

Abstract

The action of agents with well known effects on transepithelial Na transport was tested on Na extrusion in epithelial cells of the frog skin. The cells had been previously loaded with Na by incubation in cold, K-free solutions. DNP (5×10⁻⁴ M) totally inhibited Na extrusion and K uptake, while amiloride (10⁻⁵ M) did not show any effect on either of these processes. Ouabain (10⁻⁶M) and absence of K from the medium inhibited completely Na extrusion and K uptake without changing cell water content. Probably the most interesting finding is that K activated Na extrusion along a sigmoid curve, which suggests that, as in other cells, the Na pump of these epithelial cells has 2 sites for K activation. The half-activation concentration of the site with highest affinity was 0.27 mM, the other 1.3 mM. Na extrusion significantly exceeded K uptake either at low K in the medium or during initial recovery in normal K Ringer. This may indicate an electrogenic mode of pump activity.