Basolateral membrane chloride transport in isolated epithelia of frog skin

Isotopic methodology was used to characterize Cl- transport in isolated epithelia of frog skin (northern Rana pipiens) bathed in Cl--rich Ringer solution and short-circuited. Cl- content of epithelia measured when loaded to 36Cl specific activity equilibrium averaged 139.6 neq/mg dry wt. The kinetics of 36Cl efflux was biexponential and consistent with binding or compartmentalization of approximately 30% of tissue Cl- within the intracellular pool. Because efflux of 36Cl to the apical solution was immeasurable, it was concluded that apical membranes were virtually impermeable to Cl- and that basolateral membranes were highly permeable to Cl- with a mean unidirectional Cl- efflux of 21.7 microA/cm2. Both furosemide (1 mM) and 4-acetamido-4'-isothiocyanostilbene-2,2'-disulfonic acid (5 X 10(-4) M) inhibited markedly the basolateral membrane chloride fluxes within seconds, as measured in chamber experiments. As inhibition of Cl- flux occurred in the absence of a change of the electrical parameters of apical and basolateral membranes, the mechanisms of Cl- transport appeared to be electroneutral and, for the most part at least, not coupled to the fluxes of Na+ and K+. Transepithelial Cl- fluxes averaged near 1 microA/cm2, proceeding via transport routes in parallel to the cells of the stratified epithelium. No correlation existed between the "shunt" resistance measured in the presence of 100 microM amiloride (greater than 1,000 omega X cm2) and the partial conductance to Cl-.