Hydrogen ion currents in rat alveolar epithelial cells.

Alveolar epithelial cells isolated from rats and maintained in primary culture were studied using the whole-cell configuration of the "patch-clamp" technique. After other ionic conductances were eliminated by replacing permeant ions with N-methyl-D-glucamine methanesulfonate, large voltage-activated hydrogen-selective currents were observed. Like H+ currents in snail neurons and axolotl oocytes, those in alveolar epithelium are activated by depolarization, deactivate upon repolarization, and are inhibited by Cd2+ and Zn2+. Activation of H+ currents is slower in alveolar epithelium than in other tissues, and often has a sigmoid time course. Activation occurs at more positive potentials when external pH is decreased. Saturation of the currents suggests that diffusion limitation may occur; increasing the pipette buffer concentration from 5 to 120 mM at a constant pH of 5.5 increased the maximum current density from 8.7 to 27.3 pA/pF, indicating that the current amplitude can be limited in 5 mM buffer solutions by the rate at which buffer molecules can supply H+ to the membrane. These data indicate that voltage-dependent H+ currents exist in mammalian cells.