Figure 3. Effect of an intermediate... | Rockefeller University Press

Figure 3.

Effect of an intermediate voltage-independent step on the free energy estimates. (A) A six-state linear model of activation of a voltage-dependent ion channel with five closed state and a single final open state. The voltage dependence of the equilibrium constants is given by $K_{i} = K_{i}^{0} \exp (z_{i} F V β)$ (i = 1, 2, 3, 4, or 5), where $K_{i}^{0}$ is the chemical component of the equilibrium constant K_i and z_i is its voltage dependence. The third step (shown in bold) is voltage independent, and thus z₃ = 0. $Δ {\bar{G}}_{C}$ is the sum of the chemical free energy change of each of the steps and will equal $- R T \ln \prod_{i = 1}^{5} K_{i}^{0} .$ (B) Q_maxFV_m is plotted against $Δ {\bar{G}}_{C}$ for different values of log $K_{3}^{0}$ (−5 to 5) and two values of z₂ (closed squares, z₂ = 5; and open triangles, z₂ = 0). The remaining parameters of the model were arbitrarily chosen as $K_{1}^{0}$ = 1, $K_{2}^{0}$ = 75, $K_{4}^{0}$ = 25, $K_{5}^{0}$ = 5, z₁ = 2, z₃ = 0, z₄ = 2.5, and z₅ = 1. (C and D) Variation of $Δ {\bar{G}}_{C}$ (C) and V_m (D) with changing values of z₂ (0–5) and log $K_{3}^{0} .$

This Feature Is Available To Subscribers Only