Voltage-gated proton channels help regulate [pH.sub.i] in rat alveolar epithelium

Voltage-gated proton channels are expressed highly in rat alveolar epithelial cells. Here we investigated whether these channels contribute to pH regulation. The intracellular pH ([pH.sub.i]) was monitored using BCECF in cultured alveolar epithelial cell monolayers and found to be 7.13 in nominally HC[O.sub.3]-free solutions [at external pH ([pH.sub.o]) 7.4]. Cells were acid-loaded by the N[H.sup.+.sub.4] prepulse technique, and the recovery was observed. Under conditions designed to eliminate the contribution of other transporters that alter pH, addition of 10 [micro]M Zn[Cl.sub.2], a proton channel inhibitor, slowed recovery about twofold. In addition, the [pH.sub.i] minimum was lower, and the time to nadir was increased. Slowing of recovery by Zn[Cl.sub.2] was observed at [pH.sub.o] 7.4 and [pH.sub.o] 8.0 and in normal and high-[K.sup.+] Ringer solutions. The observed rate of [Zn.sup.2+]-sensitive [pH.sub.i] recovery required activation of a small fraction of the available proton conductance. We conclude that proton channels contribute to [pH.sub.i] recovery after an acid load in rat alveolar epithelial cells. Addition of Zn[Cl.sub.2] had no effect on [pH.sub.i] in unchallenged cells, consistent with the expectation that proton channels are not open in resting cells. After inhibition of all known pH regulators, slow [pH.sub.i] recovery persisted, suggesting the existence of a yet-undefined acid extrusion mechanism in these cells. proton conductance; pH regulation; hydrogen ion; acid load; 2',7'bis(2-carboxyethyl)-5(6)-carboxyfluorescein; intracellular pH