title: Distinction between high-affinity [3H]phencyclidine binding sites and muscarinic receptors in guinea-pig ileum muscle.
abstract: [3H]Phencyclidine ([3H]PCP) binding was studied in guinea-pig ileum muscle membranes. Specific binding of [3H]PCP was time dependent, reversible and saturable, with an equilibrium dissociation constant of 154 nM and maximum binding of 12.9 pmol/mg of protein at pH 9. Its pH dependency suggests that the unionized PCP is the pharmacologically active form. The binding site was on a protein which was sensitive to heat, proteolytic enzymes and the carboxylic group reagent dicyclohexylcarbodiimide, but insensitive to phospholipase A and C, concanavalin A, dithiothreitol and N-ethylmaleimide. Specific [3H]PCP binding was displaced effectively by several PCP analogs and Ca++ channel antagonists including verapamil, to which these sites had a high affinity. These high-affinity PCP-binding sites were found at a much higher concentration in the same membrane preparation than muscarinic receptor sites identified by their specific binding of [3H]quinuclidinyl benzilate. PCP bound to both sites, but with a lower affinity to the muscarinic receptor sites. The PCP and muscarinic receptor sites differed in their sensitivities to pH and drug specifities .
mesh_terms: D000818:Animals; D001665:Binding Sites; D002121:Calcium Channel Blockers / Q000494:pharmacology; D006168:Guinea Pigs; D006863:Hydrogen-Ion Concentration; D007082:Ileum / Q000378:metabolism*; D066298:In Vitro Techniques; D007473:Ion Channels / Q000378:metabolism; D010622:Phencyclidine / Q000378:metabolism* / Q000494:pharmacology; D011188:Potassium / Q000378:metabolism; D011813:Quinuclidinyl Benzilate / Q000378:metabolism; D011976:Receptors, Muscarinic / Q000032:analysis*; D014316:Tritium
chemical_list: D002121:Calcium Channel Blockers; D007473:Ion Channels; D011976:Receptors, Muscarinic; D014316:Tritium; D011813:Quinuclidinyl Benzilate; D010622:Phencyclidine; D011188:Potassium