Muscarinic M2 Receptors Coupled to Inhibition of Adenylate Cyclase in Rat Heart

大白鼠心臟香蕈素M2亞型受體接合腺核苷酸環化酶之抑制作用

魏健吾(Jiann-Wu Wei) ； 王美智(Mei-Chih Wang)

《The Chinese Journal of Physiology》 33卷4期 (1990/12) Pp. 315-327

摘要

本研究以大白鼠心臟之心室肌胞膜探討活化香蕈素M2亞型受體與腺核苷酸環化酶之抑制，兩者間的接合作用。利用不具選擇性之放射標識物((上標 3)H-QNB)與胞膜上香蕈素受體結合後，經由取代作用，計算各藥物與此受體親和力(IC50)之大小，結果顯示具選擇性之M2亞型拮抗劑（Methoctramine和AF-DX-116）比M1亞型拮抗劑（Pirenzepine和Trihexy-phenidyl）有較強的取代效價。當反應試液中無GPP(NH)p存在時，具選擇性之M2亞型作用劑（Carbachol和Oxotremorine）比M1亞型作用劑(MCN-A-343)亦有較強的取代作用。又以此心臟肌配製體測定此類藥物對腺核苷酸環化醇活性的抑制作用，也可觀察到相同事實：即具選擇性之M2亞型作用劑或拮抗劑的作用均比具有選擇性之附亞型相對藥物為強。這些藥物對於(上標 3)H-QNB結合之取代作用與對腺核苷酸環化酶作用之影響程度呈現極佳的相關性。此一事實顯示，香蕈素M2亞型受體的活化與腺核苷酸環化酶活性之抑制，兩者間具有生化上之接合作用。又GTP在此生化反應中扮演著重要角色，且GPP(NH)p可降低對M2亞型具有選擇性作用劑（Carbachol和Oxotremorine）與受體結合之親和力，故此項生化上之結合作用過程中似有G-蛋白的參與。由上述結果可知香蕈素作用劑活化大白鼠心臟上之受體而導致腺核苷酸環化酶活性之降低，係由於藥物作用於此類受體之M2亞型，且G-蛋白可能參與此結合反應。

並列摘要

The biochemical linking event between the activation of muscarinic receptors and the inhibition of adeny-late cyclase was studied with rat heart ventrical membranes. The muscarinic M2 selective antagonists were more potent than the M1 selective antagonists in the displacement of non-selective labeled (superscript 3) H-QNB binding to the membranes. This was also true for the M2 selective agonists, with respect to the Ml selective agonists, in the reaction medium without Gpp(NH)p. With the same preparation, the muscarinic M2 selective agents were also more potent than the Ml selective agents in the inhibition of adenylate cyclase activity. The order of potencies of these agents in the displacement of (superscript 3) H-QNB binding correlated well with their order of potencies in inhibiting adenylate cyclase activity. Gpp(NH)p reduced the binding affinities of M2 selective agonists (i.e. carbachol and oxotremorine), while it did not affect the binding affinities of non-selective agonist pilocarpine, M1 selective agonist McN-A-343 and antagonists (i.e. pirenzepine, trihexyphenidyl, AFDX-l16 and methoctramine). These results suggest that in the rat heart, the inhibition of adenylate cyclase by muscarinic agonists is through activation of the M2 subtype receptor and G-protein is likely to be involved in the coupling.

並列關鍵字

muscarinic M2 receptor ； inhibition of adenylate cyclase ； G-protein ； rat cardiac membranes