Differential blockade of neuronal voltage-gated Na+ and K+ channels by antidepressant drugs

The effects of a range of antidepressants were investigated on neuronal voltage-gated Na+ and K+ channels. With the exception of phenelzine, all antidepressants inhibited batrachotoxin-stimulated Na-22(+) uptake, most likely via negative allosteric inhibition of batrachotoxin binding to neurotoxin receptor site-2 on the Na+ channel. Imipramine also produced a differential action on macroscopic Na+ and K+ channel currents in acutely dissociated rat dorsal root ganglion neurons. Imipramine produced a use-dependent block of Na+ channels. In addition, there was a hyperpolarizing shift in the voltage-dependence of steady-state Na+ channel inactivation and slowed repriming kinetics consistent with imipramine having a higher affinity for the inactivated state of the Na+ channel. At higher concentrations, imipramine also blocked delayed-rectifier and transient outward K+ currents in the absence of alterations to the voltage-dependence of activation or the kinetics of inactivation. These actions on voltage-gated ion channels may underlie the therapeutic and toxic effects of these drugs. (C) 2002 Elsevier Science B.V. All rights reserved.