Sialic acid residues as catalysts for M2-muscarinic agonist-receptor interactions.
The role of sialic acid residues in the interactions of muscarinic agonists with the cardiac M2 muscarinic receptor was investigated by competitive binding experiments using the lipophilic radioligand (-)-[benzilic-4,4-3H]quinuclidinyl benzilate ([3H]QNB) and the hydrophilic ligand [N-methyl-3H]scopolamine methyl chloride ([3H]NMS). Direct labeling of the agonist binding sites was performed with the radiolabeled agonist [methyl-3H]oxotremorine M acetate ([3H]oxo-M). Neuraminidase decreased the affinity of the M2-selective agonist carbamylcholine in competitive binding experiments performed with [3H]QNB and [3H]NMS. The binding of the M1-selective agonist (4hydroxy-2-butynyl)trimethylammonium chloride m-chlorocarbanilate (McN-A-343), of the M1-selective antagonist pirenzepine, and of the M2-selective antagonist 11-([2-[(diethylamino)methyl]-1 piperidinyl]acetyl)-5,11-dihydro-6H-pyrido(2,3b)(1,4)benzodiazepin -6-on (AF-DX-116) were not affected by neuraminidase. Neuraminidase did not modify the binding parameters of 3H-antagonists but reduced the number of agonist binding sites revealed by [3H]oxo-M. The removal of sialic acid decreased the half-life of the receptor-agonist complex. The present results suggest that removal of sialic acid reduces the formation of super-high affinity agonist-receptor complexes. Sialic acid may catalyze macroscopic binding by enhancing accumulation of the agonist at the membrane surface.
Laboratoire de Neuroimmunopharmacologie, Université Louis Pasteur-Strasbourg, Illkirch, France.
E B
EB
Haddad
Y
Y
Landry
J P
JP
Gies
D008455:(4-(m-Chlorophenylcarbamoyloxy)-2-butynyl)trimethylammonium Chloride / Q000494:pharmacology; D000818:Animals; D002217:Carbachol / Q000494:pharmacology; D002462:Cell Membrane / Q000378:metabolism; D007700:Kinetics; D008297:Male; D009206:Myocardium / Q000378:metabolism*; D009439:Neuraminidase / Q000494:pharmacology*; D010095:Oxotremorine / Q000031:analogs & derivatives / Q000378:metabolism; D010276:Parasympatholytics / Q000494:pharmacology; D010890:Pirenzepine / Q000031:analogs & derivatives / Q000494:pharmacology; D011813:Quinuclidinyl Benzilate / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains; D011976:Receptors, Muscarinic / Q000187:drug effects / Q000378:metabolism*; D012601:Scopolamine / Q000378:metabolism; D012794:Sialic Acids / Q000378:metabolism*
D010276:Parasympatholytics; D011976:Receptors, Muscarinic; D012794:Sialic Acids; D010890:Pirenzepine; D008455:(4-(m-Chlorophenylcarbamoyloxy)-2-butynyl)trimethylammonium Chloride; D010095:Oxotremorine; C042743:oxotremorine M; D011813:Quinuclidinyl Benzilate; D002217:Carbachol; D012601:Scopolamine; D009439:Neuraminidase; C048593:otenzepad