Function of the Hyperpolarization-Activated Inward Rectification in Nonmyelinated Peripheral Rat and Human Axons. GRAFE, PETER, STEFAN QUASTHOFF, JULIAN GROSSKREUTZ AND CHRISTIAN ALZHEIMER. Department of Physiology, University of Munich, D-80336 Munich; Department of Neurology, Technical University of Munich, D-81675 Munich, Germany.
APStracts 3:0226N, 1996.
ABSTRACT
The function of time-dependent, hyperpolarization-activated inward rectification was analyzed on compound potentials of nonmyelinated axons in the mammalian peripheral nervous system. Isolated rat vagus nerves and fascicles of biopsied human sural nerve were tested in a three-chambered, vaseline-gap organ bath at 37 degrees C. Inward rectification was assessed by recording the effects of long-lasting hyperpolarizing currents on electrical excitability, using the method of threshold electrotonus (program QTRAC, copyright Institute of Neurology, London), and by measuring activity-dependent changes in conduction velocity and membrane potential. Prominent time- dependent, cesium-sensitive inward rectification was revealed in rat vagus and human sural nerve by recording threshold electrotonus to 200 ms hyperpolarizing current pulses. A slowing of compound action potential conduction was observed during a gradual increase in the stimulation frequency from 0.1 to 3 Hz. Above a stimulation frequency of 0.3 Hz, this slowing of conduction was enhanced during bath application of 1 mM cesium. Cesium did not alter action potential waveforms during stimulation at frequencies below 1 Hz. Cesium-induced slowing in action potential conduction was correlated with membrane hyperpolarization. The hyperpolarization by cesium was stronger during higher stimulation frequencies and small in unstimulated nerves. These data show that a cesium-sensitive, time-dependent inward rectification in peripheral rat and human nonmyelinated nerve fibers limits the slowing in conduction seen in such axons at action potential frequencies higher than about 0.3 Hz.

Received 31 May 1996; accepted in final form 11 September 1996.
APS Manuscript Number J433-6.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 5 November 1996