Gating Kinetics in Ionic Channels
It is now well established that the rising phase of the action potential seen in many nerve, muscle and cardiac cells generates from a selective increase in the membrane permeability to Na ions, PNa· When studied under voltage clamp, the changes in PNa which underlie the upstroke of the action potential are measured as changes in the electrical conductance, gNa· For a positive step change in the clamped membrane potential gNa is seen to, with a delay, rise to a peak value (activate) and then, even though the potential is held constant, to decline to a small value (inactivate). A central issue in the problem of the molecular organization of this Na channel gating machinery is the nature of the relation between the activation and inactivation processes.
KeywordsVoltage Clamp Test Pulse Tail Current Inactivation Curve Inactivation Time
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