Effect of external ammonium on the kinetics of the sodium current in frog muscle.

The effect of externally applied 20 mM NH4Cl on steady-state Na+ inactivation h infinity and other electrical parameters has been studied in voltage-clamped frog muscle fibres. Exposure to Ringer with 20 mM NH4Cl causes a small transient shift of the h infinity (E) curve to more positive potentials. Upon return to normal slowly into the original position. Similar but smaller shifts of the descending branch of the INa (E) curve, of the PNa(E) curve and of the time to peak curve are also observed. The shifts are thought to result from the changes in intracellular pH which occur during and after NH4Cl application. The observations are compatible with the idea that intracellular pH affects the surface charge potential at the inner side of the membrane.