Basolateral membrane K permselectivity and regulation in bullfrog cornea epithelium

In the isolated bullfrog cornea epithelium, under short-circuit conditions the regulation of the K permeability of the basolateral membrane was studied with conventional and K-selective microelectrodes in Cl-free Ringers. In Cl-free Ringers, the transcellular current is less than 1 microA/cm2, allowing estimation of the basolateral membrane electromotive force from measurements of the membrane voltage (Vsc). The apparent basolateral membrane K conductance was determined from measurements of the effects of single ion substitutions of K for Na on the Vsc. An increase of K from 2.5 to 25 mM on the stromal side depolarized the membrane voltage by 29 mV, whereas additional increases to 56 and 100 mM resulted in depolarizations consistent with a Nernstian prediction. In the range between 25 and 56 mM K, these decreases in membrane voltage were smaller after either decreasing the stromal-side pH from 8.1 to 7.2 or substitution of sulfate with gluconate. In contrast, preincubation with 0.1 mM ouabain did not change the membrane voltage depolarizations over any of the K ranges between 2.5 and 100 mM. Equivalent circuit analysis, based on the effects of nystatin on the electrical parameters, was used to validate the changes in the apparent basolateral membrane K conductance following increases in [K], substitution of SO4 with gluconate and Na:K pump inhibition. An increase in the [K] to 120 mM decreased the basolateral membrane resistance nearly three-fold, whereas gluconate substitution resulted in a 2.5-fold increase of the basolateral membrane resistance. This resistance increased an additional 2-fold after exposure to 5 mM Ba.(ABSTRACT TRUNCATED AT 250 WORDS)