Effects of Calcium on the Binding of Phencyclidine to Acetylcholine Receptor‐Rich Membrane Fragments from Torpedo californica Electroplaque

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Abstract
The influence of Ca on the binding of phencyclidine (PCP) to acetylcholine (ACh) receptor-rich membrane fragments was investigated. Ca decreased the equilibrium affinity for PCP in the presence, but not in the absence, of the cholinergic agonist carbamylcholine. The effect of Ca was rapidly reversible by EGTA [ethylene glycol bis(.beta.-aminoethyl ether] N,N,N'',N''-tetraacetic acid indicating that it was not attributable to Ca-activated protease or a phospholipase. Following detergent solubilization of the nicotinic ACh receptor, the Ca effect on PCP remained, suggesting that Ca may interact directly with the receptor to exert its effect. Other divalent cations (Mn2+, La2+, Co2+, Mg2+) had similar effects. A correlate of desensitization of the ACh receptor can be observed using PCP binding, and a 2-step desensitization process can be observed. Ca seemed to increase the amplitude of a rapid component of receptor desensitization. Evidently Ca plays a role in the modulation of the nicotinic ACh receptor.

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