Akhtar R A, Honkanen R E, Howe P H, Abdel-Latif A A
Department of Cell and Molecular Biology, Medical College of Georgia, Augusta.
J Pharmacol Exp Ther. 1987 Nov;243(2):624-32.
The relationships between occupancy of muscarinic acetylcholine receptors on iris sphincter muscle, measured by [3H]quinuclidinylbenzylate (QNB) binding, carbachol (CCh)-stimulated phosphatidylinositol 4,5-bisphosphate hydrolysis, measured as myo-inositol trisphosphate (IP3) accumulation, myosin light chain (MLC) phosphorylation and contraction were analyzed by examination of the dose-response relationships and the effects of the muscarinic antagonists, atropine and pirenzepine (PZ). CCh caused a concentration-dependent accumulation of IP3 (EC50 = 2.3 X 10(-6) M), MLC phosphorylation (EC50 = 3.8 X 10(-6) M), contraction (EC50 = 0.55 X 10(-6) M) and [3H]QNB displacement [KH (high affinity dissociation constant) = 2.9 X 10(-6) M]. The time course of atropine reversal of CCh-induced IP3 accumulation and muscle contraction revealed that the continued presence of activated muscarinic acetylcholine receptors was required to maintain IP3 production and contraction. Atropine was about 2 orders of magnitude more potent than PZ in inhibiting the CCh-induced biochemical and pharmacological responses and [3H] QNB binding, indicating the preponderance of M2 receptors in this smooth muscle. Thus, the PA2 values for atropine antagonism of CCh-stimulated IP3 accumulation, MLC phosphorylation and contraction were 9.1, 9.05 and 9.39, respectively, and for PZ antagonism were 7.12, 7.10 and 7.29, respectively. Furthermore, the KD values for atropine and PZ antagonism of [3H]QNB binding were 6.9 X 10(-10) and 1.5 X 10(-7) M, respectively. In addition, AF-DX116 (11-[(2-[(diethylamino)methyl]-1-piperidinyl) acetyl]-5,11-dihydro-6 H-pyrido[2,3-b][1,4]benzodiazepine-6-one), a M2 cardioselective antagonist, significantly inhibited the CCh-induced IP3 accumulation and muscle contraction.(ABSTRACT TRUNCATED AT 250 WORDS)
通过[3H]喹核醇基苯甲酸酯（QNB）结合测定虹膜括约肌上毒蕈碱型乙酰胆碱受体的占有率，通过测定肌醇三磷酸（IP3）积累来测量卡巴胆碱（CCh）刺激的磷脂酰肌醇4,5-二磷酸水解，通过检查剂量反应关系以及毒蕈碱拮抗剂阿托品和哌仑西平（PZ）的作用，分析肌球蛋白轻链（MLC）磷酸化和收缩之间的关系。CCh引起IP3浓度依赖性积累（EC50 = 2.3×10^(-6) M）、MLC磷酸化（EC50 = 3.8×10^(-6) M）、收缩（EC50 = 0.55×10^(-6) M）和[3H]QNB置换[KH（高亲和力解离常数）= 2.9×10^(-6) M]。阿托品逆转CCh诱导的IP3积累和肌肉收缩的时间过程表明，需要持续存在活化的毒蕈碱型乙酰胆碱受体来维持IP3产生和收缩。在抑制CCh诱导的生化和药理反应以及[3H]QNB结合方面，阿托品的效力比PZ高约2个数量级，表明该平滑肌中M2受体占优势。因此，阿托品拮抗CCh刺激的IP3积累、MLC磷酸化和收缩的PA2值分别为9.1、9.05和9.39，PZ拮抗的PA2值分别为7.12、7.10和7.29。此外，M2心脏选择性拮抗剂AF-DX116（11-[(2-[(二乙氨基)甲基]-1-哌啶基)乙酰]-5,11-二氢-6H-吡啶并[2,3-b][1,4]苯二氮杂卓-6-酮）显著抑制CCh诱导的IP3积累和肌肉收缩。（摘要截短于250字）
