[Stimulus dependent sodium channel blockade in node of Ranvier membranes by the quaternary antiarrhythmic N-propyl ajmaline (neogiluritmal)].

The blocking action of neo-gilurytmal (NG), a quaternary derivative of aimalin, on sodium channels was studied in the voltage-clamped node of Ranvier. NG exerted no action on the resting membrane unless the repetitive pulsing was turned on. A series of repetitive depolarizing pulses of short duration (5 ms) produced the accumulating "stimulus-dependent" blockade of sodium channels. The rate and degree of the blockade increased with the increasing of pulse voltage even over the potential range where all the sodium channels were open. Recovery from the blockade occurred within several tens of minutes. Unlike the repetitive pulsing, long-lasting (1 s) depolarization of the membrane produced only a slight increase in the blockade of sodium channels. Elimination of sodium inactivation by aconitine prevented the blocking action of NG. The results of the experiments indicate that NG blocks only the open sodium channels with intact inactivation gate.