Effect of Ba2+ and furosemide on K+ and Rb+ secretion and absorption in isolated frog skin.

The aim of the present investigation was to explore whether in isolated frog skin there should be different pathways for K+ absorption and secretion. Therefore, the unidirectional fluxes of 42K+ and the K+-like isotope 86Rb+ were measured. By using various transport inhibitors, separate pathways for active K+ absorption and secretion were detected. The data obtained indicate that the transepithelial K+ and Rb+ transport across isolated frog skin is made up of four different components: one passive and three active. One of the active components is directed from the apical to the basolateral solution, whereas the other two are in the opposite direction. The direction of the net K+ transport depends on the activities of these three active transport components. The active uptake mechanism, which is present in the epithelial cells, discriminates between K+ and Rb+. The ratio between the K+ and Rb+ influxes, K/Rb, is about 3. The presence of Ba2+, furosemide or ouabain in the apical solution had no effect on the K+ influx. The active secretion of K+ takes place via two different pathways, namely the skin glands and the epithelial cells. The K+ secretion via the glands is inhibited by furosemide (basolateral), but is unaffected by Ba2+ (apical) and does not discriminate between K+ and Rb+. The active K+ secretion via the epithelial cells is blocked by apical Ba2+, and it discriminates between K+ and Rb+. The ratio between the K+ and Rb+ effluxes is about 2. The data presented show that the K+ channels in the apical and the basolateral membrane of the epithelial cells discriminate between K+ and Rb+.(ABSTRACT TRUNCATED AT 250 WORDS)