Copper-induced alteration of muscarinic binding in bovine adrenal medulla

In microsomes of bovine adrenal medulla, there were two affinity binding sites for carbamylcholine with a high and a low affinity. Copper (1-10 microM) largely enhanced the affinity of carbamylcholine at the low affinity binding site, with a slight increase in the affinity at the high affinity binding site. On the other hand, copper slightly decreased the binding affinity of pirenzepine and atropine. Thus, low concentrations of copper modulate the muscarinic receptors in the adrenal medulla by selectively increasing agonist affinity.