1. 1. The electrophysiological effects of veratridine, cevadine and aconitine (10-8-2 × 10-4, 2 × 10-7-2 × 10-6 and 2 × 10-6-10-4 mol/l, respectively) were compared on frog muscle membrane using conventional microelectrodes. 2. 2. Veratridine and aconitine were equally effective in depolarizing the resting membrane with the threshold concentration of 5 × 10-5 mol/l. 3. 3. Volleys of repetitive discharges and slow transient depolarizations were observed when single electrical stimuli were applied in the presence of veratridine (5 × 10-8-2 × 10-5 mol/l), but not aconitine. Volleys with aconitine could be evoked only by repetitive stimulation; however, no tendency of repolarization was observed following these volleys. Two orders of magnitude more aconitine than veratridine was required to induce volleys with similar parameters. 4. 4. The effects of cevadine were similar to those of the corresponding concentrations of veratridine. 5. 5. The observed differences between the electrophysiological actions of aconitine and veratrum alkaloids may be explained in part with differences in Na+ channel inactivation produced by these toxins, in addition to differences in their use-dependent behavior.
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