A slow component in the gating current of the frog node of Ranvier

The slow component of the gating current on-response has been studied on voltage-clamped nodes of Ranvier of the frog Rana esculenta. At 0 mV and 20° C the charge and the time constant of the slow component were on average 37.1 fC and 0.39 ms, respectively. The slow component could be abolished by shifting the holding potential from its usual value (–100 mV) to –60 mV. Repolarization to –100 mV for 2 ms was sufficient for complete recovery of the slow component. The local anaesthetic benzocaine (1 mM) reduced the fast component (measured at 0 mV) on average to 54% and the slow component (also measured at 0 mV) to 70% of the control value. In the potential range from –60 to 60 mV the charge of the slow component increased slightly with voltage. No significant voltage dependence of its time constant was observed. The slow component most likely reflects charge movement between different open states; it does not seem to be related to inactivation of the sodium channels or activation of the potassium channels.