Demonstration of a receptor in Torpedo synaptic vesicles for the acetylcholine storage blocker L-trans-2-(4-phenyl[3,4-3H]-piperidino) cyclohexanol.

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Transport and storage of acetylcholine by purified Torpedo electric organ synaptic vesicles is blocked by the drug L-trans-2-(4-phenylpiperidino)cyclohexanol (AH-5183). This study sought evidence of a specific receptor for the drug. Highly tritiated L-trans-2-(4-phenyl [3,4-3H] piperidino)-cyclohexanol (L-[3H] AH5183) was synthesized. An excess of nonradioactive L-isomer competed with L-[3H]AH5183 for binding to purified Torpedo synaptic vesicles whereas nonradioactive D-isomer did so poorly. Dissociation of bound L-[3H]AH5183 was first order with a rate constant at 23 degrees C of 0.23 +/- 0.03 min-1, and association was too rapid to study. At equilibrium the amount of L-[3H]AH5183 bound at saturation varied in different vesicle preparations, but in one typical preparation specific binding of 181 +/- 15 pmol L-[3H]AH5183 per mg of synaptic vesicle protein was observed with a dissociation constant of 34 +/- 6 nM. Neither acetylcholine nor choline compete effectively with L-[3H]AH5183 for binding. The evidence suggests that about 3.7 +/- 0.3 enantioselective receptors for L-[3H]AH5183 are typically present in each cholinergic synaptic vesicle, and the L-AH5183 binding site does not recognize acetylcholine.

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