Voltage and Ca2+ Activation of Single Large-Conductance Ca2+-Activated K+ Channels Described by a Two-Tiered Allosteric Gating Mechanism

Author:

Rothberg Brad S.1,Magleby Karl L.1

Affiliation:

1. Department of Physiology and Biophysics, University of Miami School of Medicine, Miami, Florida 33101-6430

Abstract

The voltage- and Ca2+-dependent gating mechanism of large-conductance Ca2+-activated K+ (BK) channels from cultured rat skeletal muscle was studied using single-channel analysis. Channel open probability (Po) increased with depolarization, as determined by limiting slope measurements (11 mV per e-fold change in Po; effective gating charge, qeff, of 2.3 ± 0.6 eo). Estimates of qeff were little changed for intracellular Ca2+ (Ca2+i) ranging from 0.0003 to 1,024 μM. Increasing Ca2+i from 0.03 to 1,024 μM shifted the voltage for half maximal activation (V1/2) 175 mV in the hyperpolarizing direction. V1/2 was independent of Ca2+i for Ca2+i ≤ 0.03 μM, indicating that the channel can be activated in the absence of Ca2+i. Open and closed dwell-time distributions for data obtained at different Ca2+i and voltage, but at the same Po, were different, indicating that the major action of voltage is not through concentrating Ca2+ at the binding sites. The voltage dependence of Po arose from a decrease in the mean closing rate with depolarization (qeff = −0.5 eo) and an increase in the mean opening rate (qeff = 1.8 eo), consistent with voltage-dependent steps in both the activation and deactivation pathways. A 50-state two-tiered model with separate voltage- and Ca2+-dependent steps was consistent with the major features of the voltage and Ca2+ dependence of the single-channel kinetics over wide ranges of Ca2+i (∼0 through 1,024 μM), voltage (+80 to −80 mV), and Po (10−4 to 0.96). In the model, the voltage dependence of the gating arises mainly from voltage-dependent transitions between closed (C-C) and open (O-O) states, with less voltage dependence for transitions between open and closed states (C-O), and with no voltage dependence for Ca2+-binding and unbinding. The two-tiered model can serve as a working hypothesis for the Ca2+- and voltage-dependent gating of the BK channel.

Publisher

Rockefeller University Press

Subject

Physiology

Reference97 articles.

1. Calcium-activated potassium channels expressed from cloned complementary DNAs;Adelman;Neuron.,1992

2. A new look at the statistical model identification;Akaike;IEEE Trans. Auto. Control.,1974

3. Gating currents and charge movements in excitable membranes;Almers;Rev. Physiol. Biochem. Pharmacol.,1978

4. Editorialgraphic representation of the results of kinetic analyses;Andersen;J. Gen. Physiol,1999

5. A component of calcium-activated potassium channels encoded by the Drosophila slo locus;Atkinson;Science.,1991

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