ABSTRACT
Cycloheximide depresses maximum rate of change in membrane potential observed during the rising phase of the action potential in single medullated axons of Xenopus. To,e course of depression is independent of cycloheximide concentration over a range that almost completely inhibits leucine incorporation into axonal proteins.
Subject(s)
Action Potentials/drug effects , Axons/drug effects , Cycloheximide/pharmacology , Nerve Tissue Proteins/biosynthesis , Animals , Dose-Response Relationship, Drug , Electric Conductivity , Sodium/metabolism , XenopusABSTRACT
Repetitive stimulation of a single medullated nerve fiber of Xenopus yields a succession of postspike voltage-time curves which are nearly coincident until attainment of a voltage that corresponds to that of the maximum attained by the normal postspike undershoot. Initially the interspike potential returns toward a resting level after this brief phase of hyperpolarization. However, as tetanization proceeds, a pattern of hyperpolarization develops with the result that, in the tetanic steady state, there exists a progressive hyperpolarization throughout each interspike interval. Extent of postspike hyperpolarization in terms of a deviation deltaVm from the resting level of membrane potential is approximated by the variation deltaVm = delta[MNa + MK]/[GNa + GK] where MNa and MK are current densities associated with active pumping of sodium and potassium ions and GNa and GK are corresponding time-dependent leak conductances. Tetanic hyperpolarization is reversibly abolished by cyanide and by exposure to lithium Ringer. Eventual reappearance of tetanic hyperpolarization in the presence of lithium Ringer suggests lithium pumping.
