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Acetylcholine Transport and Drug Inhibition Kinetics in Torpedo Synaptic Vesicles
Author(s) -
Bahr Ben A.,
Parsons Stanley M.
Publication year - 1986
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1111/j.1471-4159.1986.tb00640.x
Subject(s) - vesicle , synaptic vesicle , acetylcholine , chemistry , torpedo , dissociation constant , biophysics , non competitive inhibition , transporter , kinetics , cooperativity , biochemistry , membrane , acetylcholine receptor , biology , pharmacology , enzyme , receptor , physics , quantum mechanics , gene
Steady‐state initial velocity uptake of [ 3 H]acetylcholine ([ 3 H]ACh) by purified Torpedo electric organ synaptic vesicles was studied. Transport specific activity decreased at higher vesicle concentration. Michaelis‐Menten type kinetics describe [ 3 H]ACh active transport at constant vesicle concentration with no evidence of cooperativity or transporter heterogeneity. The ACh dissociation constant is about 0.3 m M , transport has a maximal velocity of about 1.6 nmol/min/mg protein, and both are dependent on the vesicle preparation. Nonradioactive ACh was a competitive inhibitor with respect to [ 3 H]ACh. The potent transport inhibitor dl ‐ trans ‐2‐(4‐phenylpiperidino)cyclohexanol (AH5183) is a non‐competitive inhibitor with respect to [ 3 H]ACh, with an inhibition constant of 41 ± 7 n M. Inhibition by AH5183 is reversible. The results suggest that AH5183 does not bind to the ACh transporter recognition site on the outside of the vesicle membrane, and thus it might inhibit allosterically.