Evidence for negative gating charges in Myxicola axons

In Myxicola giant axons, the total amount of intramembrane charge available to move over the range -80 to + 120 mV decreases by 23% when the external pH is reduced from 7.3 to 5.5. The remaining charge moves more slowly at the onset of depolarizing pulse, but the rate of charge movement at the end of the pulse is unchanged. In contrast to acidic external pH, intramembrane charge movements are insensitive to alkaline external pH or any change in the internal pH. The results are consistent with a hypothesis in which a portion of the initial outward gating current consists of titratable negative charges moving inward.