Whole-cell recordings of a voltage-gated channel at ( ) give the open probabilities below

PHYSICS · Subjective · Fermi University Physics · Biophysics & Medical Physics · Molecular machines, transport and bioenergetics · Bioelectricity, the senses and the physics of the body

Forces, Machines and Signals, Ch Channels, pumps and the resting potential

Problem

Whole-cell recordings of a voltage-gated channel at 298 K298\,\mathrm{K} (kBT/e=25.7 mVk_BT/e = 25.7\,\mathrm{mV}) give the open probabilities below, fitted by the two-state gating curve Po(V)=11+e−zappe(V−V1/2)/kBTP_o(V) = \dfrac{1}{1 + e^{-z_{\rm app}e(V-V_{1/2})/k_BT}}. Data: V=−40 mVV=-40\,\mathrm{mV}, Po=0.0068P_o=0.0068; V=−20 mVV=-20\,\mathrm{mV}, Po=0.500P_o=0.500; V=0 mVV=0\,\mathrm{mV}, Po=0.993P_o=0.993. Find the apparent gating charge zappz_{\rm app} and the midpoint voltage V1/2V_{1/2}.

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