Effects of cyanide at different concentrations on single nerve fibers

¹ Department of Physiology, Washington University School of Medicine, Saint Louis, Missouri

At a constant pH of 9.0, with continuous perfusion of tris-buffered Ringer's solution, free of HCO₃ and PO₄, the time course of cyanide depression of frog single nerve-fiber spike height is independent of cyanide concentration within a range of 1 or 2–10 mm NaCN. Similar results are obtained during a transient period of increased rate of cyanide depression induced by forced feeding. Maximal limiting responses obtained during hyperpolarization are constant throughout the 1st hr of cyanide action. These data are taken to indicate that cyanide depresses the steady-state level of the sodium conductance h factor before it produces any appreciable change in the Na equilibrium potential as a result of interference with the metabolically linked Na-K exchange mechanism. It is concluded that cyanide blocks a chain of reactions at a link remote from the step directly concerned with maintenance of sodium conductance.