Sialic acid residues as catalysts for M2-muscarinic agonist-receptor interactions

Mol Pharmacol. 1990 May;37(5):682-8.

Abstract

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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • (4-(m-Chlorophenylcarbamoyloxy)-2-butynyl)trimethylammonium Chloride / pharmacology
  • Animals
  • Carbachol / pharmacology
  • Cell Membrane / metabolism
  • Kinetics
  • Male
  • Myocardium / metabolism*
  • Neuraminidase / pharmacology*
  • Oxotremorine / analogs & derivatives
  • Oxotremorine / metabolism
  • Parasympatholytics / pharmacology
  • Pirenzepine / analogs & derivatives
  • Pirenzepine / pharmacology
  • Quinuclidinyl Benzilate / metabolism
  • Rats
  • Rats, Inbred Strains
  • Receptors, Muscarinic / drug effects
  • Receptors, Muscarinic / metabolism*
  • Scopolamine / metabolism
  • Sialic Acids / metabolism*

Substances

  • Parasympatholytics
  • Receptors, Muscarinic
  • Sialic Acids
  • Pirenzepine
  • (4-(m-Chlorophenylcarbamoyloxy)-2-butynyl)trimethylammonium Chloride
  • Oxotremorine
  • oxotremorine M
  • Quinuclidinyl Benzilate
  • Carbachol
  • Scopolamine
  • Neuraminidase
  • otenzepad