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J. Gen. Physiol.,
Volume 111, Number 5, May 1, 1998 625-638
From the * Department of Anesthesiology, Fast inactivating Shaker H4 potassium channels and nonconducting pore mutant Shaker H4 W434F
channels have been used to correlate the installation and recovery of the fast inactivation of ionic current with
changes in the kinetics of gating current known as "charge immobilization" (Armstrong, C.M., and F. Bezanilla.
1977. J. Gen. Physiol. 70:567-590.). Shaker H4 W434F gating currents are very similar to those of the conducting
clone recorded in potassium-free solutions. This mutant channel allows the recording of the total gating charge
return, even when returning from potentials that would largely inactivate conducting channels. As the depolarizing potential increased, the OFF gating currents decay phase at Department of Molecular and Medical Pharmacology, and § Department of Physiology,
University of California, Los Angeles, Los Angeles, California 90095-1778; and Conicet, Buenos Aires, Argentina 1033
90 mV return potential changed from a single
fast component to at least two components, the slower requiring ~200 ms for a full charge return. The charge immobilization onset and the ionic current decay have an identical time course. The recoveries of gating current
(Shaker H4 W434F) and ionic current (Shaker H4) in 2 mM external potassium have at least two components. Both
recoveries are similar at 120 and 90 mV. In contrast, at higher potentials (70 and 50 mV), the gating
charge recovers significantly more slowly than the ionic current. A model with a single inactivated state cannot account for all our data, which strongly support the existence of "parallel" inactivated states. In this model, a fraction of the charge can be recovered upon repolarization while the channel pore is occupied by the NH2-terminus
region.
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