Tocainide blocks Na currents by accumulation of inactivated Na channels

The effect of tocainide on the voltage-dependent parameters of Na permeability was studied in voltage clamp experiments performed in single myelinated rat and frog nerve fibres. The main effect of tocainide was a potential- and frequency-dependent block of Na channels in both species. There was no shift to the voltage-dependent parameters of steady state Na activation (m infinity) or of the time constants of Na activation (tau m) and inactivation (tau h) along the potential axis.