title: Partial functional reconstitution of the cardiac muscarinic cholinergic receptor.
abstract: Digitonin-solubilized cardiac muscarinic receptors were reconstituted by dialysis into human erythrocyte acceptor membranes which lack high-affinity muscarinic receptors. The number of receptors reconstituted was proportional to the quantity of soluble receptors added to the reconstitution system. Specific [3H](-)-quinuclidinyl benzilate binding to the reconstituted receptor was found to be saturable with a Kd (dissociation constant) equal to 48 +/- 4 pM and a Bmax (maximal density of binding sites) equal to 50 +/- 5 fmol/mg of protein. Competitive binding studies indicated that the reconstituted receptors showed stereoselectivity and drug specificity consistent with a high-affinity muscarinic receptor. Agonist binding to the reconstituted receptor was decreased by the addition of guanyl-5'-yl imidodiphosphate. Sixty per cent of the reconstituted receptors were found to be integral membrane proteins. The molecular weight of the reconstituted receptor as determined by sodium dodecyl sulfate-gel electrophoresis was 76,000 +/- 2,000 and was identical to the molecular weight of the muscarinic receptor in the original cardiac membranes. The data indicate that a partially functional, intact muscarinic receptor was reconstituted into human erythrocyte acceptor membranes and that membrane constituents may be required to stabilize the receptor in a high-affinity state for antagonists.
mesh_terms: D001667:Binding, Competitive; D004072:Digitonin; D006801:Humans; D007700:Kinetics; D009206:Myocardium / Q000378:metabolism*; D011813:Quinuclidinyl Benzilate / Q000378:metabolism; D011976:Receptors, Muscarinic / Q000302:isolation & purification / Q000378:metabolism*; D012995:Solubility
chemical_list: D011976:Receptors, Muscarinic; D011813:Quinuclidinyl Benzilate; D004072:Digitonin