Effects of thiamine antagonists on nerve conduction. II. Voltage clamp experiments with antimetabolites

Thiamine antimetabolites were externally applied to voltage clamped squid giant axons to investigate the possible role of thiamine in nerve conduction. Phenylthiazinothiamine, in concentrations as low as 250 muM, reduced peak early current and steady-state current, with the depression of the former being two to five times greater than that of the latter. Peak transient and steady-state conductances were about equally depressed by thiamine tert-butyl disulfide (2 mM) and L-586944-00P07 (5-10 mM). None of the antimetabolites produced an appreciable change in the kinetics of Na+ activation, K+ activation, or Na+ inactivation. Thiamine itself, applied externally up to 30 mM, had no appreciable effect on either the magnitude or time course of the ionic currents. Although these data are consistent with the hypothesis that thiamine may be involved in nerve conduction, they probably reflect a nonspecific stabilizing interaction of this class of compound with the axon membrane. Taken in this light, the hypothesis that thiamine plays a direct role in Na+ channel permeability changes must be reevaluated.