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Figure 7. . A more complex model of mSlo gating suggests errors in our ΔG(0)o-c estimates at low [Ca2+]. (A). Diagram of the model Horrigan et al. (1999) used to described the voltage-dependent gating of the mSlo channel. Horizontal transitions represent voltage sensor activation. Vertical transitions represent the conformational change by which the channel opens. JC(V) and JO(V) are the equilibrium constants for voltage-sensor activation when the channel is either closed or open where: JC(V) = JC(0)exp(zFV/RT) and JO(V) = JO(0)exp(zFV/RT); and L(V) is the equilibrium constant between open and closed when no voltage sensors are active and no Ca2+ is bound where: L(V) = L(0)exp(qFV/RT). (B) 50-state mSlo model. Here Ca2+ binding occurs along the long horizontal axis, voltage sensor movement along the short horizontal axis, and transitions from the upper to the lower tier indicate channel opening. The front face of this scheme corresponds to the model in A. (C) Simulated G-V curves from the model in B at the [Ca2+] indicated on the figure. For more discussion of this model see (Cox and Aldrich, 2000; Cui and Aldrich, 2000; Rothberg and Magleby, 2000). Parameters were as follows: JC(0) = 0.066; JO(0) = 1.10; z = 0.51; L(0) = 2e-6; q = 0.4; KC = 10 μM, KO = 1 μM. Each curve is fitted with a Boltzmann function (dashed lines). (D) Plots of ΔG(0)o-c as a function of [Ca2+] for the model in C. Darkened circles indicate the true ΔG(0)o-c of the model calculated as 4RTln[(1+ [Ca]/KC)/(1 + [Ca]/KO)] + 4RTln[(1 + JC(0))/(1 + JO(0))] − RTln[L(0)], while the open circles represent estimates obtained from Boltzmann-fit parameters as zFV1/2.

Image published in: Bao L et al. (2002)

Copyright © 2002, The Rockefeller University Press. Creative Commons Attribution-NonCommercial-ShareAlike license

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