The single channel basis of slow inactivation of na+ channels in
rat skeletal muscle.
Ruff, Robert L.
Departments of Neurology and Neurosciences, Cleveland Veterans
Administration Medical Center, Case Western Reserve University
Medical School, Cleveland, Ohio
APStracts 3:0105C, 1996.
This study examined the single channel basis of slow inactivation of
Na + currents (I Na ) in rat fast twitch skeletal muscle fibers. A
loose patch voltage clamp monitored changes in the maximum inward I
Na as the holding potential of the membrane patch changed. On a
neighboring region of extrajunctional membrane of the same fiber a
giga-ohm seal patch voltage clamp recorded single channel I Na . The
maximum number of simultaneously open Na + channels among a group of
current traces indicated the maximum number of excitable channels.
The holding potentials of the two voltage clamps were the same. Slow
inactivation did not affect the open time or conductance of single Na
+ channels. The number of excitable Na + channels reversibly
decreased during development of slow inactivation of I Na and
increased during recovery from slow inactivation of I Na . Different
stimulation protocols examined whether Na + channels had to be in the
closed, open or fast inactivated states to enter the slow inactivated
state. Na + channels appear to be able to enter the slow inactivated
state from the closed, open or fast inactivated state.
Received 4 December 1995; accepted in final form 11 March 1996.
APS Manuscript Number C725-5.
Article publication pending Am. J. Physiol. (Cell Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 16 April 96