Implications of an anomalous intracellular electrical response in bullfrog corneal epithelium.

The ionic dependencies of the transepithelial and intracellular electrical parameters were measured in the isolated frog cornea. In NaCl Ringer's the intracellular potential difference Vsc measured under short-circuit conditions depolarized by nearly the same amount after either increasing the stromal-side KCl concentration from 2.5 to 25 mM or exposure to 2 mM BaCl2 (K+ channel blocker). With Ba2+ the depolarization of the Vsc by 25 mM K+ was reduced to one-quarter of the control change. If the Cl-permselective apical membrane resistance Ro remained unchanged, the relative basolateral membrane resistance Ri, which includes the lateral intercellular space, increased at the most by less than twofold after Ba2+. These effects in conjunction with the depolarization of the Vsc by 62 mV after increasing the stromal-side K+ from 2.5 to 100 mM in Cl-free Ringer's as well as the increase of the apparent ratio of membrane resistances (a = Ro/Ri) from 13 to 32 are all indicative of an appreciable basolateral membrane K+ conductance. This ratio decreased significantly after exposure to either 25 mM K+ or Ba2+. The decline of Ro/Ri with 25 mM K+ appears to be anomalous since this decrease is not consistent with just an increase of basolateral membrane conductance by 25 mM K+, but rather perhaps a larger decrease of Ro than Ri. Also an increase of lateral space resistance may offset the effect of decreasing Ri with 25 mM K+. In contrast, Ro/Ri did transiently increase during voltage clamping of the apical membrane potential difference Vo and exposure to 25 mM K+ on the stromal side.(ABSTRACT TRUNCATED AT 250 WORDS)