Dataset Information

Voltage-controlled gating in a large conductance Ca2+-sensitive K+channel (hslo).

ABSTRACT: Large conductance calcium- and voltage-sensitive K+ (MaxiK) channels share properties of voltage- and ligand-gated ion channels. In voltage-gated channels, membrane depolarization promotes the displacement of charged residues contained in the voltage sensor (S4 region) inducing gating currents and pore opening. In MaxiK channels, both voltage and micromolar internal Ca2+ favor pore opening. We demonstrate the presence of voltage sensor rearrangements with voltage (gating currents) whose movement and associated pore opening is triggered by voltage and facilitated by micromolar internal Ca2+ concentration. In contrast to other voltage-gated channels, in MaxiK channels there is charge movement at potentials where the pore is open and the total charge per channel is 4-5 elementary charges.

SUBMITTER: Stefani E

PROVIDER: S-EPMC24695 | biostudies-literature | 1997 May

REPOSITORIES: biostudies-literature

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Voltage-controlled gating in a large conductance Ca2+-sensitive K+channel (hslo).

Stefani E E Ottolia M M Noceti F F Olcese R R Wallner M M Latorre R R Toro L L

Proceedings of the National Academy of Sciences of the United States of America 19970501 10

Large conductance calcium- and voltage-sensitive K+ (MaxiK) channels share properties of voltage- and ligand-gated ion channels. In voltage-gated channels, membrane depolarization promotes the displacement of charged residues contained in the voltage sensor (S4 region) inducing gating currents and pore opening. In MaxiK channels, both voltage and micromolar internal Ca2+ favor pore opening. We demonstrate the presence of voltage sensor rearrangements with voltage (gating currents) whose movement ...[more]

PMID: 9144254

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Project description:The Ca2+-dependent gating mechanism of large-conductance calcium-activated K+ (BK) channels from cultured rat skeletal muscle was examined from low (4 microM) to high (1,024 microM) intracellular concentrations of calcium (Ca2+i) using single-channel recording. Open probability (Po) increased with increasing Ca2+i (K0. 5 11.2 +/- 0.3 microM at +30 mV, Hill coefficient of 3.5 +/- 0.3), reaching a maximum of approximately 0.97 for Ca2+i approximately 100 microM. Increasing Ca2+i further to 1,024 microM had little additional effect on either Po or the single-channel kinetics. The channels gated among at least three to four open and four to five closed states at high levels of Ca2+i (>100 microM), compared with three to four open and five to seven closed states at lower Ca2+i. The ability of kinetic schemes to account for the single-channel kinetics was examined with simultaneous maximum likelihood fitting of two-dimensional (2-D) dwell-time distributions obtained from low to high Ca2+i. Kinetic schemes drawn from the 10-state Monod-Wyman-Changeux model could not describe the dwell-time distributions from low to high Ca2+i. Kinetic schemes drawn from Eigen's general model for a ligand-activated tetrameric protein could approximate the dwell-time distributions but not the dependency (correlations) between adjacent intervals at high Ca2+i. However, models drawn from a general 50 state two-tiered scheme, in which there were 25 closed states on the upper tier and 25 open states on the lower tier, could approximate both the dwell-time distributions and the dependency from low to high Ca2+i. In the two-tiered model, the BK channel can open directly from each closed state, and a minimum of five open and five closed states are available for gating at any given Ca2+i. A model that assumed that the apparent Ca2+-binding steps can reach a maximum rate at high Ca2+i could also approximate the gating from low to high Ca2+i. The considered models can serve as working hypotheses for the gating of BK channels.

Dataset Information

Voltage-controlled gating in a large conductance Ca2+-sensitive K+channel (hslo).

Publications

Voltage-controlled gating in a large conductance Ca2+-sensitive K+channel (hslo).

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