Solubilization and characterization of guanine nucleotide‐sensitive muscarinic agonist binding sites from rat myocardium

Abstract

Muscarinic receptors from rat myocardial membranes may be solubilized by digitonin in good yield at low temperatures in the presence of Mg2+. Under these conditions, up to 60% of the soluble receptors show high affinity binding for the potent agonist [3H]-oxotremorine-M (KA = 10(9)M-1), which is inhibited by 5'-guanylylimidodiphosphate. The muscarinic binding site labelled with [3H]-oxotremorine-M has a higher sedimentation coefficient (13.4 s) than sites labelled with a 3H antagonist in the presence of guanylylimidodiphosphate (11.6 s) and probably represents a complex between the ligand binding subunit of the receptor and a guanine nucleotide binding protein.