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Relaxation measurements on the acetylcholine receptor

Sheridan, Robert E. and Lester, Henry A. (1975) Relaxation measurements on the acetylcholine receptor. Proceedings of the National Academy of Sciences of the United States of America, 72 (9). pp. 3496-3500. ISSN 0027-8424. PMCID PMC433021.

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In Electrophorus electroplaques, the agonist-induced postsynaptic conductance depends on membrane potential. During steady exposure to agonists, after a voltage step the conductance relaxes on a millisecond time scale, exponentially approaching a new equilibrium value. The relaxation rate constant k is an instantaneous function of voltage, insensitive to the past or present conductance. Two components sum to form k. A concentration-sensitive component increases linearly with agonist concentration and decreases during desensitization or exposure to curare. Thus this component reflects the average frequency at which acetylcholine receptors are opening. The voltage-sensitive component, obtained by extrapolating k to zero agonist concentration, increases at more positive potentials. For acetylcholine, the voltage-sensitive component equals the rate constant for the exponential decay of postsynaptic currents; it thus seems to be the closing rate for active receptors. The voltage-sensitive component has the relative amplitudes acetylcholine < carbamoylcholine < decamethonium, and for each agonist equals the closing rate determined from "noise" measurements at neuromuscular junctions. The kinetic data explain several aspects of the steady-state conductance induced by agonists, but shed no light on apparent cooperative effects.

Item Type:Article
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URLURL TypeDescription CentralArticle
Lester, Henry A.0000-0002-5470-5255
Additional Information:© 1975 by the National Academy of Sciences. Communicated by James Olds, June 25, 1975. We thank F. Sigworth for constructing the voltage-clamp circuit, D. Williams for technical assistance, and N.J.M. Birdsall, J.-P. Changeux, T. Jovin, W. Newsome, M.A. Raftery, and G. Zweig for helpful discussion. This work was supported by NIH Grant NS-11756, by an NSF Predoctoral Fellowship (to R.E.S.), and by an Alfred P. Sloan Fellowship (to H.A.L.).
Funding AgencyGrant Number
NSF Predoctoral FellowshipUNSPECIFIED
Alfred P. Sloan FoundationUNSPECIFIED
Subject Keywords:synaptic transmission; voltage clamp; ion channels; Electrophorus electroplaque
Issue or Number:9
PubMed Central ID:PMC433021
Record Number:CaltechAUTHORS:SHEpnas75
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:7740
Deposited By: Tony Diaz
Deposited On:31 Jul 2007
Last Modified:05 Oct 2020 17:15

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