Currents Related to Movement of the Gating Particles of the Sodium Channels

“…IT seems difficult to escape the conclusion that the changes in ionic permeability depend on the movement of some component of the membrane which behaves as though it had a large charge or dipole moment”¹. With these words Hodgkin and Huxley predicted the existence of gating currents: charge movement associated with molecular rearrangements that attend the opening and closing of the ionic channels in response to changes in the membrane field. The polarity of gating current of the sodium channels can be easily predicted: following a positive step change of membrane voltage, positively charged gating particles would move outward through the membrane field from closed to open position (or negatively charged particles would move inward), yielding an outward current. On repolarization after a voltage step that opened the channels, gating current would be inward, as particles moved from open to closed position. Hodgkin and Huxley were unable to observe gating currents experimentally, and concluded that the density of ionic channels in the membrane must be low. A later attempt by Chandler and Meves² to detect such currents was also unsuccessful, and they estimated that there are less than 100 sodium channels μm⁻², a prediction that has been borne out by later estimates of sodium channel density^3,4. We report here that by use of signal averaging techniques, we have observed small transient currents which we believe are the gating currents of the sodium channels.