Intracellular voltage of isolated epithelia of frog skin: apical and basolateral cell punctures

Isolated epithelia of frog skin were prepared with collagenase, and the cells were punctured with intracellular microelectrodes across their apical (outer) and basolateral (inner) surfaces. Regardless of the route of cell puncture, the intracellular voltage (Vosc) in short- circuited isolated epithelia was markedly negative, averaging -70.4 mV for apical punctures and -91.6 mV for basolateral punctures. As in intact epithelia, amiloride outside caused the Vosc to become more negative (means of -96.7 and -101.8 mV), with a concomitant increase in the resistance of the apical barrier. Increasing the [K)i of the basolateral solution from 2.4 to 8.0 or 14.4 mM caused rapid step depolarization (5-10 s) of the Vosc under transepithelial Na transporting and amiloride-inhibited conditions of Na transport, with the delta Vosc ranging between 23.9 and 68.3 mV per decade change of [K]i. The finding that the Vosc of isolated epithelia of frog skin is independent of the route of cell penetration is consistent with the notion that the cells of the stratified epithelium are electrically coupled (functional syncitium). Moreover, the isolated epithelium can serve as a useful preparation, especially in studies designed to investigate the properties of the basolateral surfaces of cells.