Characterization of M1- and M2-muscarinic receptors in calf retina membranes.
Muscarinic receptors are identified in bovine retina membranes by the specific binding of 1-[benzilic-4,4'-3H]-quinuclidinyl benzilate [3H]-QNB. Binding occurs to one population of non-cooperative binding sites: KD = 0.11 +/- 0.02 nM and Bmax = 0.61 +/- 0.07 pmol/mg protein. Competition binding curves of the M1-selective antagonist pirenzepine are shallow. Computer-analysis reveals the presence of 45 +/- 1% M1-receptors (high affinity sites for pirenzepine, Ki = 31 +/- 10 nM). The remaining low affinity sites (Ki = 1.0 +/- 0.3 microM) are denoted as M2-receptors. Competition binding curves with the agonist carbachol are shallow as well. 1 mM GTP causes a rightward shift and a steepening of the carbachol curve, whereas 1 mM N-ethylmaleimide (NEM) provokes a leftward shift and also a steepening of the curve. The GTP effect is abolished by NEM. Binding of the antagonists [3H]-QNB, atropine or pirenzepine is not modulated by GTP nor by NEM.
Vanderheyden
P
P
Department of Protein Chemistry, Free University of Brussels, St Genesius-Rode, Belgium.
Ebinger
G
G
Vauquelin
G
G
D000818:Animals; D001667:Binding, Competitive; D002217:Carbachol / Q000493:pharmacokinetics; D002417:Cattle; D005033:Ethylmaleimide / Q000493:pharmacokinetics; D006160:Guanosine Triphosphate / Q000493:pharmacokinetics; D010890:Pirenzepine / Q000493:pharmacokinetics; D011813:Quinuclidinyl Benzilate / Q000031:analogs & derivatives / Q000493:pharmacokinetics; D011976:Receptors, Muscarinic / Q000032:analysis* / Q000378:metabolism; D012160:Retina / Q000032:analysis*
C044493:1-benzilic-4,4'-quinuclidinyl benzilate; D011976:Receptors, Muscarinic; D010890:Pirenzepine; D011813:Quinuclidinyl Benzilate; D006160:Guanosine Triphosphate; D002217:Carbachol; D005033:Ethylmaleimide