The rate at which the postjunctional membrane of muscle fibers becomes desensitized to the action of carbamylcholine is increased after the muscle has been soaked in solutions containing increased concentrations of calcium. Some further aspects of this effect of calcium were investigated by measuring changes in the input resistance of single fibers of the frog sartorius during local perfusion of the neuromuscular junction with 2.73 x 10-3 M carbamylcholine in isolated muscles immersed in 165 mM potassium acetate. It was found that (a) sudden changes in the local concentration of calcium brought about by perfusing fibers with carbamylcholine solutions containing 20 mM calcium, 40 mM oxalate, or 40 mM EDTA were followed within 20 sec by marked changes in the rate of desensitization; (b) prior to 13 sec after the introduction of carbamylcholine, however, no effect on the input resistance could be detected even though the muscle had been presoaked in 10 mM calcium; (c) the ability of high concentrations of calcium to bring about rapid desensitization disappears when a lower concentration of carbamylcholine (0.137 x 10-3 M) is applied to the muscle fiber. These findings suggest that calcium present in the extracellular fluid can act directly on the postjunctional membrane to promote the desensitization process and that an increased permeability of the membrane to calcium brought about by the presence of carbamylcholine is a factor which contributes to this action.
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September 01 1970
Further Studies of the Effect of Calcium on the Time Course of Action of Carbamylcholine at the Neuromuscular Junction
Arthur A. Manthey
Arthur A. Manthey
From the Department of Physiology and Biophysics, University of Tennessee Medical Units, Memphis, Tennessee 38103
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Arthur A. Manthey
From the Department of Physiology and Biophysics, University of Tennessee Medical Units, Memphis, Tennessee 38103
Received:
February 19 1970
Online ISSN: 1540-7748
Print ISSN: 0022-1295
Copyright © 1970 by The Rockefeller University Press
1970
J Gen Physiol (1970) 56 (3): 407–419.
Article history
Received:
February 19 1970
Citation
Arthur A. Manthey; Further Studies of the Effect of Calcium on the Time Course of Action of Carbamylcholine at the Neuromuscular Junction . J Gen Physiol 1 September 1970; 56 (3): 407–419. doi: https://doi.org/10.1085/jgp.56.3.407
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