Portal de Periódicos da CAPES

Apparent cooperative effects in acetylcholine receptor-mediated ion flux in electroplax membrane preparations

1976; Elsevier BV; Volume: 69; Issue: 3 Linguagem: Inglês

10.1016/0006-291x(76)90950-5

1090-2104

George P. Hess, John Andrews, Gary E. Struve,

Neuroscience and Neuropharmacology Research

The kinetics of acetylcholine receptor-mediated flux of 22sodium ions from microsacs has been measured in the presence of activators (carbamylcholine and decamethonium) and an inhibitor (d-tubocurarine) of neural transmission. The dependence of the first-order rate constant, kobs, for 22sodium ion efflux on either decamethonium or carbamylcholine concentration does not exhibit cooperativity. The apparent cooperativity observed by Kasai and Changeux in dose-response curves for 22sodium flux from the same preparation is adequately accounted for by the contribution which efflux from non-excitable microsacs, the main component of the preparation, makes to the measurements. d-Tubocurarine was found to be a non-competitive inhibitor of decamethonium-activated 22sodium efflux. The results of the kinetic measurements are in agreement with equilibrium measurements of the interaction of decamethonium with the same microsac preparation, i.e. adherence to a classic Langmuir binding isotherm and separate binding sites for activators and inhibitors of neural activity. The results indicate a direct relationship between ligand binding and receptor-mediated ion flux. How these two processes contribute to electrophysiological measurements is not apparent.