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 http://resolver.caltech.edu/CaltechAUTHORS:SHEpnas75
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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.
|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.).|
|Subject Keywords:||synaptic transmission; voltage clamp; ion channels; Electrophorus electroplaque|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Tony Diaz|
|Deposited On:||31 Jul 2007|
|Last Modified:||26 Dec 2012 09:34|
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