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. 2006 Dec;128(6):731–744. doi: 10.1085/jgp.200609596

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Copyright © 2006, The Rockefeller University Press

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Figure 2. — Effects on 0 Ca²⁺ logP_O-V relation by changes in L₀, Vh_O, Vh_C, and z_J. (A) BK channel gating scheme at 0 Ca²⁺ according to the HA model. Channel resides in either open (O) or closed (C) conformation, with zero to four (subscripts) activated (A) voltage sensors. L is the C-O equilibrium constant with all four voltage sensors in the resting (R) state (dashed box). J is the R-A equilibrium constant when channels are closed. D is the allosteric interaction factor between C-O transition and voltage sensor activation. Equilibrium between C-O transitions is allosterically regulated by the states of four independent and identical voltage sensors. (B) Simulated 0 Ca²⁺ logP_O-V relation according to the HA model (L₀ = 1 e⁻⁶, z_L = 0.30 e₀, z_J = 0.58 e₀, Vh_C = +200 mV, Vh_O = +50 mV). Dashed line represents linear fit of the logP_O-V relation at the limiting slope. L₀ (point where dashed line and zero line cross) and z_L (slope of dashed line) are the zero voltage value of L and its partial charge, respectively. (C) Effects on logP_O-V relation of changing L₀ from 1 e⁻⁶ (black) to 1 e⁻⁸ (red). Notice the shift of the limiting slope along the Y axis. (D) Effects on logP_O-V relation of changing Vh_O (−50 mV, red), Vh_C (+100 mV, green), or z_J (0.4 e₀, blue) and leaving other parameters the same as in B (black). Notice reducing Vh_O, but not Vh_C or z_J shifts the steep phase of the logP_O-V relation to more hyperpolarized potentials.