The kinetics of [3H]N-methylscopolamine binding to membranes of Chinese hamster ovary (CHO) cells expressing muscarinic M1-M4acetylcholine receptors was studied. [3H]N- methylscopolamine dissociation was used for the "single-point" analysis of allosteric modulation by vinburnine (L-eburnamonine). [3H]N-methylscopolamine dissociation was decelerated by vinburnine with EC50values of 29.5, 4.1, 9.5 and 15.0 μM for muscarinic M1-M4receptors, respectively. Acetylcholine doubled the EC50of vinburnine for muscarinic M3receptors. These kinetic EC50values correlated with equilibrium binding constants, supporting the ternary allosteric model. Vinburnine also decelerated the association of [3H]N-methylscopolamine binding, resulting in opposite cooperativity for muscarinic M1and M2receptors. © 2003 Elsevier B.V. All rights reserved.
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