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 ~ 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 μA/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 μA/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 μM amiloride (> 1,000 Ω·cm2) and the partial conductance to Cl-.
ASJC Scopus subject areas
- Cell Biology