Kinetic properties of electrostatic pores with orientable dipoles, for Na+ and K+ transport through biological membranes.

The model, used previously to account for the transport of K+ ions through squid axon membranes under steady-state conditions, is extended to the description of the kinetic behavior of Na+ and K+ currents, for sudden variations of the applied potential. Theoretical curves are obtained by numerical integration of the electrodiffusion equation for ions within pores, with variable boundary conditions resulting from a progressive reorientation of dipoles at the pore surface. The pores are supposed to be selective and the dipole parameters are allowed to be different for Na+ and K+ pores. The K+ current varies with time, in agreement with the K+ dipole parameters deduced from the steady-state results of Gilbert and Ehrenstein (1969). The dipole parameters for Na+ current are deduced from the steady-state results of Armstrong, Bezanilla & Rojas (1973), where the inactivation phase of the Na+ current is suppressed by introducing pronase in the inside solution. The dipole reorientation is relavent to explain the sigmoid shape of the activation phase of the Na+ current, while the inactivation phase seems to resort to another physical mechanism. The predictions based on this model agree with the experimental results for the steady-state negative resistance and the gating current, associated both with a reorientation of surface dipoles, as well as the activation phase of the Na+ current using a consistent set of parameters for all these comparisons.