EFFECTS OF CARBAMAZEPINE ON THE IONIC CONDUCTANCES OF MYXICOLA GIANT AXONS

¹ Departments of Neurological Sciences and Biomedical Engineering, Rush Medical College, Chicago, Illinois

Carbamazepine (Tegretol) in concentrations of 0.25 to 1.0 mM reduces both the sodium and potassium conductances of voltage-clamped Myxicola giant axons. These effects are dose-dependent, reversible and develop with the same time course. The effects of the drug are slightly more pronounced on the sodium channel, 0.5 mM carbamazepine causing an average decrease in maximum sodium conductance of 50%, while decreasing potassium conductance by 40%. In addition to these effects, the leakage current for hyperpolarizing voltage steps is reduced, and the membrane is reversibly depolarized by 0 to 10 mV. There is little or no effect of carbamazepine on the rate constants governing the time-dependent behavior of the membrane conductances, or on the position of the conductance-voltage curves along the voltage axis. This behavior is in contrast to the relatively specific effect exerted by diphenylhydantoin on the sodium conductance in squid axons.