Krouse, Mauri E. and Lester, Henry A. and Wassermann, Norbert H. and Erlanger, Bernard F. (1985) Rates and Equilibria for a Photoisomerizable Antagonist at the Acetylcholine Receptor of Electrophorus Electroplaques. Journal of General Physiology, 86 (2). pp. 235-256. ISSN 0022-1295 http://resolver.caltech.edu/CaltechAUTHORS:20120628-075949869
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Voltage-jump and light-flash experiments have been performed on isolated Electrophorus electroplaques exposed simultaneously to nicotinic agonists and to the photoisomerizable compound 2,2'-bis-[α-(trimethylammonium)methyl]-azobenzene (2BQ). Dose-response curves are shifted to the right in a nearly parallel fashion by 2BQ, which suggests competitive antagonism; dose-ratio analyses show apparent dissociation constants of 0.3 and 1 µM for the cis and trans isomers, respectively. Flash-induced trans → cis concentration jumps produce the expected decrease in agonist-induced conductance; the time constant is several tens of milliseconds. From the concentration dependence of these rates, we conclude that the association and dissociation rate constants for the cis-2BQ-receptor binding are approximately ~ 10^8 M^(-1) s^(-1) and 60 s^(-1) at 20ºC; the Q_(10) is 3. Flash-induced cis → trans photoisomerizations produce molecular rearrangements of the ligand-receptor complex, but the resulting relaxations probably reflect the kinetics of buffered diffusion rather than of the interaction between trans-2BQ and the receptor. Antagonists seem to bind about an order of magnitude more slowly than agonists at nicotinic receptors.
|Additional Information:||© 1985 The Rockefeller University Press. Original version received 24 September 1984 and accepted version received 29 March 1985. We thank R. Spencer for assistance in all phases of the project and J. M. Nerbonne, J. Pine, and D. Van Essen for advice. This research was sponsored by the National Institutes of Health (research grants NS-11756 and NS-15581) and by a grant-in-aid from the Muscular Dystrophy Association of America. M.E.K. was supported in part by predoctoral training grants from the National Institutes of Health (GM-07737) and by the Weigle Memorial Fund.|
|Official Citation:||Rates and equilibria for a photoisomerizable antagonist at the acetylcholine receptor of Electrophorus electroplaques. M E Krouse, H A Lester, N H Wassermann, and B F Erlanger 86:235-256. doi:10.1085/jgp.86.2.235|
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|Deposited By:||Ruth Sustaita|
|Deposited On:||28 Jun 2012 15:19|
|Last Modified:||26 Dec 2012 15:25|
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