Kinetic studies on the effects of ouabain on Na+ fluxes in frog skin

Abstract

Among 48 pieces of paired frog skins of Rana pipiens in Ringer's solution, 10 pieces showed a strictly monotone decrease in the short circuit current (SCC) following ouabain treatment (10(-4) M). In 9 cases a transient attenuation, and in 27 cases a distinct wave in the ebb of the SCC, was seen. In 2 instances, two waves were seen. Associated with the not-monotone events was a transient rise in electrical skin conductance. The reasons for these mixed skin responses are unknown. One possible reason is considered here: Early during the ouabain action, some of the Na+ entering from the mucosal side is trapped in the skin by electroneutral processes, in keeping with the already known fact that ultimately cellular KCl is partly replaced by NaCl. Computer assisted model studies show how monotone, and not-monotone "transepithelial" net Na+ flux curves can be generated. Essential conditions for the generation of not-monotone Na+ flux curves are: 1. Presence of two distinct "cellular", active Na+ pools in the model. 2. Presence of a loop pathway in which a principal "transepithelial Na+ transport compartment", and a constituent "Na+/K+ maintenance compartment", are connected to each other and to the "extracellular" compartment. The model, then, predicts under which kinetic conditions monotone and not-monotone transepithelial Na+ flux curves will be seen.

Effects of standard diuretics and ortho‐vanadate on sodium transport across isolated frog skin

“…The slow onset of action is probably due to slow diffusion of the drug to the site of Na+-K+-ATPase, which is located at the basolateral membranes of the epithelium in frog skin (Farquhar & Palade 1966, Mills et al 1977. As previously noted for frog skin (Huf et al 1982) and for other sodium-transporting epithelia, we found a biphasic response, i.e. an initial decrease followed by a transient increase in SCC and PD.…”