Comparison of the effects of Anemonia toxin II on sodium and gating currents in frog myelinated nerve

Abstract

(1) Na + and gating currents were measured in myelinated frog nerve fibres without and in the presence of 7 μM Anemonia toxin II in the extracellular solution. (2) From the experiments, kinetic parameters of Na + currents and of gating charge displacements during (‘on’ response) and after (‘off’ response) depolarizations were determined. (3) The following parallel modifications of Na + currents and charge displacements by Anemonia toxin II were observed: the toxin reduces the maximum Na + permeability and the ‘on’ charge displacement; Na + activation and ‘on’ charge displacement become faster; Na + inactivation and the decline of the ‘off’ charge displacement with increasing pulse duration (charge immobilization) are prolonged; slow components of ‘on’ charge displacements are diminished. (4) The observations support the notion that the fast ‘on’ charge displacement is connected with the process of Na + activation, while Na + inactivation is linked to charge immobilization. Our experiments suggest that slow ‘on’ charge displacements during longer depolarizations are correlated with the process of Na + inactivation.