Two Types of Ach Receptors Contribute to Fast Channel Gating on Mouse
Skeletal Muscle.
Dawn Shepherd and Paul Brehm.
Department of Neurobiology and Behavior, SUNY at Stony Brook, Stony Brook,
NY, 11794 .
APStracts 4:192N, 1997.
ABSTRACT
Single channel recordings from mouse C2 myotubes indicate that maturation of
skeletal muscle is accompanied by the appearance of two types of 'fast' Ach
receptor channels which are each functionally distinct from the embryonic
receptor type present at early stages of differentiation. The embryonic
receptor type has a low conductance (45pS) and long channel open time,
rendering slowly decaying synaptic currents. One 'fast' channel type which
appears during muscle maturation is distinguished from the embryonic receptor
type on the basis of both higher conductance (65pS) and shorter open time.
However, single channel recordings from differentiated C2 muscle point to the
existence of a second 'fast' receptor type which has a conductance similar to
the embryonic receptor type (45pS), but significantly reduced mean channel
open time. Analyses of individual channel function at high Ach concentrations
directly demonstrate the co-existence of two kinetically distinct types of 45
pS Ach receptors. Openings by 'fast' type and 'slow' embryonic type of 45 pS
receptors occurred in bursts allowing distinction on the basis of both mean
open time and open probability for individual receptors. The embryonic type of
45 pS receptor has an open time approximately two fold longer than the 'fast'
receptor counterpart. Additional differences were reflected in the open
probability distributions for 'fast' and 'slow' 45 pS receptor types. Both
types of 45 pS receptor were kinetically distinguishable from the 65 pS
receptor. We found no support for the idea that the 'slow' and 'fast' 45 pS
receptor types result from the interconversion of dual gating modes involving
the same receptor protein. Our results are consistent with the idea that the
acquisition of fast synaptic current decay, required at mature neuromuscular
synapses is due to the up-regulation of two distinct 'fast' types of nicotinic
Ach receptors during skeletal muscle development.
Received 25 February 1997; accepted in final form 12 August 1997.
APS Manuscript Number J160-7.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1997 The American Physiological Society.
Published in APStracts on 28 August 1997