ACTIVATION OF POTASSIUM CONDUCTANCE AND SODIUM PUMP BY ACTION POTENTIALS IN RABBIT VAGAL C-FIBERS

Potential changes of C-fibers in rabbit vagus nerves were recorded with the sucrose gap method. The hyperpolarization following single action potentials, bursts of action potentials, and repeated bursts was modeled as the sum of two decaying exponentials. Only the slower decaying component was caused by electrogenic sodium-potassium pumping as shown by its sensitivity to ouabain and substitution of isethionate with chloride. The sensitivity to external potassium changes showed that the faster component was caused by a potassium current. The amplitude and time constant of this component increased with burst frequency and duration in a manner similar to the calcium dependent potassium conductance. In low sodium, this component appeared as a slow ouabain-insensitive potential. Anomalous results were obtained in low calcium so that involvement of other potential dependent conductances could not be excluded. How activation of these currents may modify action potential conduction in C-fibers is discussed.