Testing for Detailed Balance (Microscopic Reversibility) in IonChannel Gating

Abstract

The gating of ion channels is subject to the thermodynamicprinciple of detailed balance (microscopic reversibility). Inthe absence of an external energy source driving the gating,the number of transitions in each direction between any twostates should (on average) be equal at thermodynamic equi-librium so that the single-channel record shows time revers-ibility (Colquhoun and Hawkes, 1982, 1995). For gatingmechanisms in which states are connected in loops, detailedbalance is preserved if the product of the rate constants inthe clockwise direction around each loop is equal to theproduct of the rate constants in the counterclockwise direc-tion around the same loop (Colquhoun and Hawkes, 1982,1995). A violation of detailed balance would indicate thepresence of an external energy source, as in the gating ofCl channels from Torpedo, where the external energysource is the Cl gradient (Richard and Miller, 1990).In a recent paper published in the