Effect of the blocked inactivation of sodium channels on intracellular and extracellular action potentials from isolated frog muscle fibres.

The intra- and extracellular action potentials of isolated frog muscle fibres, treated with ATX II for blocking sodium inactivation, are investigated. In concentrations of 0.1 to 0.5 X 10(-6) M, ATX II leads to a considerable change of the repolarization phase of the intracellular potential, with a tendency toward achieving a plateau-type potential. In addition to the intracellular action potentials, extracellular action potentials were also recorded from the same fibres. Immediately next to the fibre membrane and at a small radial distance the extracellular potentials did not manifest essential differences compared with recordings under normal physiological conditions. Conclusions are reached about the influence of the blocked Na-inactivation on the intra- and extracellular action potentials of muscle fibres.