Takahashi T, Kurosawa S, Owyang C
Department of Internal Medicine, University of Michigan, Medical Center, Ann Arbor 48109-0362.
Am J Physiol. 1994 Oct;267(4 Pt 1):G523-8. doi: 10.1152/ajpgi.1994.267.4.G523.
Carbachol (10(-8)-10(-3) M) produced two distinct biochemical responses in the guinea pig gallbladder smooth muscle: simulation of phosphoinositide (PI) hydrolysis and inhibition of forskolin-mediated adenosine 3',5'-cyclic monophosphate (cAMP) formation in a dose-dependent manner. The mean effective dose (ED50) concentration (1.6 x 10(-5) M) of carbachol-mediated stimulation of PI hydrolysis was 145 times greater than the ED50 concentration (1.1 x 10(-7) M) of carbachol mediated inhibition of cAMP formation. The inhibitory effect of carbachol on cAMP formation was antagonized by the pretreatment of pertussis toxin. To determine whether these two biochemical responses were mediated by the same or different subtypes of muscarinic receptors, the relative potencies of muscarinic receptor antagonists were calculated by Schild analysis. The M3 muscarinic antagonist 4-diphenylacetoxy-N-methylpiperidine methiodide (4-DAMP) exhibited inhibitory constant (Ki) values at 0.3 and 1.2 nM in antagonizing the stimulation of PI hydrolysis and the inhibition of cAMP formation, respectively. The corresponding Ki values for pirenzepine, a muscarinic M1 antagonist, were 11 and 130 nM. The corresponding Ki values for AF-DX 116, a muscarinic M2 antagonist, were 34 and 450 nM. Thus 4-DAMP was 37x and 108x more potent than pirenzepine in antagonizing the stimulation of PI hydrolysis and the inhibition of cAMP formation, respectively. In addition, compared with AF-DX 116, 4-DAMP was 113x and 375x more potent in reducing stimulation of PI hydrolysis and inhibition of cAMP formation. Cholecystokinin (CCK) octapeptide (10(-10)-(10-6) M) caused a significant increase of PI hydrolysis but had no inhibitory effects on cAMP formation evoked by forskolin (10(-5) M).(ABSTRACT TRUNCATED AT 250 WORDS)
卡巴胆碱（10⁻⁸ - 10⁻³ M）在豚鼠胆囊平滑肌中产生两种不同的生化反应：模拟磷酸肌醇（PI）水解，并以剂量依赖的方式抑制福斯高林介导的3',5'-环磷酸腺苷（cAMP）生成。卡巴胆碱介导的PI水解刺激的平均有效剂量（ED50）浓度（1.6×10⁻⁵ M）比卡巴胆碱介导的cAMP生成抑制的ED50浓度（1.1×10⁻⁷ M）高145倍。百日咳毒素预处理可拮抗卡巴胆碱对cAMP生成的抑制作用。为了确定这两种生化反应是由同一种还是不同亚型的毒蕈碱受体介导，通过Schild分析计算了毒蕈碱受体拮抗剂的相对效价。M3毒蕈碱拮抗剂4-二苯基乙酰氧基-N-甲基哌啶甲基碘化物（4-DAMP）在拮抗PI水解刺激和cAMP生成抑制时，其抑制常数（Ki）值分别为0.3和1.2 nM。毒蕈碱M1拮抗剂哌仑西平的相应Ki值分别为11和130 nM。毒蕈碱M2拮抗剂AF-DX 116的相应Ki值分别为34和450 nM。因此，在拮抗PI水解刺激和cAMP生成抑制方面，4-DAMP的效力分别比哌仑西平高37倍和108倍。此外，与AF-DX 116相比，4-DAMP在减少PI水解刺激和cAMP生成抑制方面的效力分别高113倍和375倍。胆囊收缩素（CCK）八肽（10⁻¹⁰ - 10⁻⁶ M）可显著增加PI水解，但对福斯高林（10⁻⁵ M）诱发的cAMP生成无抑制作用。（摘要截短于250字）
