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.
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