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Functional Stoichiometry at the Nicotinic Receptor. The Photon Cross Section for Phase 1 Corresponds to Two Bis-Q Molecules per Channel

Sheridan, Robert E. and Lester, Henry A. (1982) Functional Stoichiometry at the Nicotinic Receptor. The Photon Cross Section for Phase 1 Corresponds to Two Bis-Q Molecules per Channel. Journal of General Physiology, 80 (4). pp. 499-515. ISSN 0022-1295. PMCID PMC2228709. doi:10.1085/jgp.80.4.499.

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These experiments examine changes in the agonist-induced conductance that occur when the agonist-receptor complex is perturbed. Voltage-clamped Electrophorus electroplaques are exposed to the photoisomerizable agonist trans-Bis-Q A 1-µs laser flash photoisomerizes some trans-Bis-Q molecules bound to receptors; because the cis configuration is not an agonist, receptor channels close within a few hundred microseconds. This effect is called phase 1. We compare (a) the fraction of channels that close during phase 1 with (b) the fraction of trans-Bis-Q molecules that undergo trans → cis photoisomerization. Parameter a is measured as the fractional diminution in voltage-clamp currents during phase 1. Parameter b is measured by changes in the optical spectra of Bis-Q solutions caused by flashes . At low flash intensities, a is twice b, which shows that the channel can be closed by photoisomerizing either of two bound agonist molecules. Conventional dose-response studies with trans-Bis-Q also give a Hill coefficient of two. As a partial control for changes in the photochemistry caused by binding of Bis-Q to receptors, spectral measurements are performed on the photoisomerizable agonist QBr, covalently bound to solubilized acetylcholine receptors from Torpedo. The bound and free agonist molecules have the same photoisomerization properties. These results verify the concept that the open state of the acetylcholine receptor channel is much more likely to be associated with the presence of two bound agonist molecules than with a single such molecule.

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Lester, Henry A.0000-0002-5470-5255
Additional Information:© 1982 Rockefeller University Press. After the Initial Publication Period, RUP will grant to the public the non-exclusive right to copy, distribute, or display the Article under a Creative Commons Attribution-Noncommercial-Share Alike 4.0 International license, as described at, or updates thereof. Received for publication 24 November 1981; in revised form 27 May 1982. We thank S . Dunn, J. Racs, and M. A. Raftery for providing the receptor-rich membrane fragments from Torpedo and for performing the α-bungarotoxin binding assays . We thank N. H. Wassermann and B. F. Erlanger for supplying the Bis-Qand QBr. We also thankM. E. Krouse, J. Nerbonne, and J. Pine for advice. This research was supported by the National Institutes of Health (RCDA NS-272 to H.A .L . and grant NS-11756) and by a grant from the Muscular Dystrophy Associations of America.
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Muscular Dystrophy Association of AmericaUNSPECIFIED
Issue or Number:4
PubMed Central ID:PMC2228709
Record Number:CaltechAUTHORS:20120717-113744311
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Official Citation:Functional stoichiometry at the nicotinic receptor. The photon cross section for phase 1 corresponds to two bis-Q molecules per channel. R E Sheridan and H A Lester J Gen Physiol 1982 80:499-515. Published October 1, 1982, doi:10.1085/jgp.80.4.499
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:32516
Deposited On:17 Jul 2012 19:50
Last Modified:09 Nov 2021 21:27

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