AJP - Regulatory, Integrative and Comparative Physiology, Vol 254, Issue 3 443-R452, Copyright © 1988 by American Physiological Society
A slow potassium conductance after action potential bursts in rabbit vagal C fibers
R. M. Siegel and R. I. Birks
Department of Physiology, McGill University, Montreal, Quebec, Canada.
Sucrose gap recordings were made from vagus nerve in rabbit to examine the
mechanisms underlying the generation of the hyperpolarization that follows
a burst of evoked action potentials in unmyelinated C fibers. Analysis of
the posttetanic hyperpolarization was made by fitting the membrane
potential changes with the sum of two exponential components. The
posttetanic hyperpolarization consisted of two separable components with
time constants of approximately 0.5 and 30 s. The slower exponentially
decaying component was dependent on an increase in electrogenic sodium
pumping as shown by the effect of ouabain and changes in extracellular
chloride. The faster-decaying exponential component was caused by a
potassium conductance as shown by the effect of varied extracellular
potassium. This potassium conductance appears to be novel as its dynamics
vary with the frequency and duration of the burst yet increases in reduced
calcium. It is suggested that this slow decaying and modifiable potassium
conductance can play a role in modulation of preganglionic and presynaptic
action potential conduction.
