The effect of metacaine on the slow variation of peak sodium currents in potential clamped Ranvier nodes following changes in holding potential.

The effect of changes in the holding potential on peak sodium currents in isolated myelinated nerve fibres (peak INa) was investigated with the conventional sodium inactivation being kept at h infinity = 1. In Ringer solution no stationary values of peak INa could be obtained over the potential range tested. Near the normal resting potential, ER, peak INa changed with time clearly even after 10 min. Therefore, the individual values of peak INa as normalized by peak INa at ER and corrected for the unevitable run-down of peak INa could not serve as measure for stationary values of any membrane parameter. Under metacaine (1 mmol/l) peak INa changed comparably faster and proved to be less potential dependent as compared to peak INa of the untreated fibre. The effects observed are not necessarily governed by a specific process located inside the nodal membrane.