Dependence of tetanic hyperpolarization on pump conductance in the cyanide-treated Xenopus node

Prolonged exposure to cyanide leads to a delayed but reversible disappearance of tetanic hyperpolarization in the Xenopus node (G. M. Schoepfle, Am. J. Physiol. 231, 1033–1038, 1976). This effect is attributed to a pronounced decline in the absolute values of the ATP and ADP concentrations, such that the ATP-driven ion translocation is no longer possible, regardless of the existing values for (Na) i, (K) i and the(ATP)/(ADP) ratio. Mathematically, this would imply a vanishing of a constant pump conductance g p in the exression for electrogenic pump current density J p , where J p = g p(V m - E p) in which V m is membrane potential and E p is an ATP- and sodium-dependent e.m.f.