Charge dissociation and the rising phase of gating currents.

Gating currents from voltage-sensitive channels are generally attributed to the translocation or redistribution of ionic charge associated with the channel molecule. Such charge moves in the direction of the applied field to produce a decreasing current in the external circuit. An early rising phase for the gating current is observed for a number of channel systems and might be either some special kinetic redistribution of charge or an experimental artifact. A model that produces net charge in the channel through sequential molecular dissociation of a charged channel segment gives a rising phase for the gating current. Translocation of the charged segment produces the decay phase for a biphasic gating current. This kinetic molecular explanation constitutes a physical explanation for the biphasic gating currents that is consistent with present views of channel structure.