Gating currents: the role of nonlinear capacitative currents of electrostrictive origin

The nonlinear capacitative currents deriving from electrostrictive changes of membrane capacitance have been calculated under conditions similar to those employed by Armstrong and Bezanilla (1974) and Keynes and Rojas (1974) in their experiments on gating currents. For values of the parameter characterizing membrane electrostriction in the range suggested by optical retardation studies of Cohen et al. (1971), the nonlinear current of electrostrictive origin is comparable in magnitude and time-course, but is opposite in direction to the observed gating currents. Hence, the a priori neglect of electrostrictive currents is probably not justified. Conversely, if this current is, in fact, negligibly small in real situations, it follows that membrane compressibility must be significantly smaller than has been estimated.