Haddad E B, Landry Y, Gies J P
Laboratoire de Neuroimmunopharmacologie, Université Louis Pasteur-Strasbourg, Illkirch, France.
Mol Pharmacol. 1990 May;37(5):682-8.
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.
通过使用亲脂性放射性配体（-）-[苯甲酰-4,4-³H]喹核醇基苯甲酸酯（[³H]QNB）和亲水性配体[甲基-³H]东莨菪碱甲基氯（[³H]NMS）的竞争性结合实验，研究了唾液酸残基在毒蕈碱激动剂与心脏M2毒蕈碱受体相互作用中的作用。用放射性标记的激动剂[甲基-³H]氧化震颤素M醋酸盐（[³H]氧代-M）对激动剂结合位点进行直接标记。在使用[³H]QNB和[³H]NMS进行的竞争性结合实验中，神经氨酸酶降低了M2选择性激动剂氨甲酰胆碱的亲和力。M1选择性激动剂（4-羟基-2-丁炔基）三甲基氯化铵间氯卡班酸盐（McN-A-343）、M1选择性拮抗剂哌仑西平和M2选择性拮抗剂11-（[2-[(二乙氨基)甲基]-1-哌啶基]乙酰基）-5,11-二氢-6H-吡啶并(2,3-b)(1,4)苯二氮䓬-6-酮（AF-DX-116）的结合不受神经氨酸酶影响。神经氨酸酶未改变³H-拮抗剂的结合参数，但减少了[³H]氧代-M显示的激动剂结合位点数量。唾液酸的去除降低了受体-激动剂复合物的半衰期。目前的结果表明，唾液酸的去除减少了超高亲和力激动剂-受体复合物的形成。唾液酸可能通过增强激动剂在膜表面的积累来催化宏观结合。
