Proton channels in snail neurons studied with surface pH glass microelectrodes

Surface pH was recorded on voltage-clamped snail neurons with Hinke-type glass microelectrodes. During stepwise depolarization from -50 mV to +40 mV the surface pH usually increased at first and then fell rapidly during each 7.5 sec voltage step. The pH changes appeared to be due to proton passage through voltage-sensitive channels. The pH changes were inhibited by cadmium and zinc, and were not as sensitive to external pH as to internal pH. Changes in internal pH lagged behind surface pH. Changes in external calcium had little effect on the surface pH increases seen with small depolarizations. These results confirm earlier conclusions that depolarization opens proton-permeable channels.