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J. Gen. Physiol.,
Volume 112, Number 6, December 1, 1998 679-713
From * The Howard Hughes Medical Institute and The voltage-dependent gating mechanism of KAT1 inward rectifier potassium channels was studied
using single channel current recordings from Xenopus oocytes injected with KAT1 mRNA. The inward rectification
properties of KAT1 result from an intrinsic gating mechanism in the KAT1 channel protein, not from pore block
by an extrinsic cation species. KAT1 channels activate with hyperpolarizing potentials from Department of Molecular and Cellular Physiology, Stanford University School of
Medicine, Stanford, California 94305
110 through 190
mV with a slow voltage-dependent time course. Transitions before first opening are voltage dependent and account for much of the voltage dependence of activation, while transitions after first opening are only slightly voltage dependent. Using burst analysis, transitions near the open state were analyzed in detail. A kinetic model with
multiple closed states before first opening, a single open state, a single closed state after first opening, and a
closed-state inactivation pathway accurately describes the single channel and macroscopic data. Two mutations
neutralizing charged residues in the S4 region (R177Q and R176L) were introduced, and their effects on single
channel gating properties were examined. Both mutations resulted in depolarizing shifts in the steady state conductance-voltage relationship, shortened first latencies to opening, decreased probability of terminating bursts,
and increased burst durations. These effects on gating were well described by changes in the rate constants in the
kinetic model describing KAT1 channel gating. All transitions before the open state were affected by the mutations, while the transitions after the open state were unaffected, implying that the S4 region contributes to the
early steps in gating for KAT1 channels.
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