Sandirasegarane Lakshman, Diamond Jack
Division of Pharmacology and Toxicology, Faculty of Pharmaceutical Sciences, University of British Columbia, Vancouver, B.C., Canada.
Pharmacology. 2004 Jan;70(1):46-56. doi: 10.1159/000074242.
Previous studies have shown that muscarinic inhibition of cardiac contractility is mediated by either activation of nitric oxide (NO)/guanosine 3',5'-cyclic monophosphate (cGMP) pathway or stimulation of inhibitory G protein (G(i)). However, it still remains controversial as to whether NO/cGMP pathway or G(i) protein or both mediate(s) the negative inotropic effect of muscarinic agonists in adult ventricular myocytes. In the present study that involves the use of adult rat ventricular myocytes, the muscarinic agonist, carbachol, inhibited beta-adrenergic (isoproterenol) stimulation of contractility (cell shortening) by 82% and increased cGMP levels by 49% within 6 min. Pretreatment of myocytes with soluble guanylyl cyclase inhibitor (1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one, ODQ) or NO synthase inhibitor (N(G)-monomethyl-L-arginine, L-NMMA) for 30 min blocked carbachol-induced increases in cGMP levels. However, neither ODQ nor L-NMMA pretreatment had any effect on carbachol inhibition of isoproterenol-induced contractility. In addition, carbachol did not attenuate increases in myocyte contractility induced by forskolin (a direct activator of adenylyl cyclase) or 8-(4-chlorophenylthio)-adenosine 3',5'-cyclic monophosphate (a cell-permeable cAMP analog which activates cAMP-dependent protein kinase). Pretreatment of myocytes with G(i) protein inhibitor, pertussis toxin (PTX, 1 microg/ml), for 18-20 h abolished carbachol inhibition of isoproterenol-induced contractility. Furthermore, in ventricular myocytes isolated 3 days after in vivo treatment of rats with PTX (3 microg/100 g, i.p.), there was a complete loss of the negative inotropic effect of carbachol. These data indicate that pertussis toxin-sensitive G protein but not NO/cGMP pathway is required for muscarinic inhibition of beta-adrenoceptor-mediated increases in contractility in adult rat ventricular myocytes.
先前的研究表明，毒蕈碱对心肌收缩力的抑制作用是通过一氧化氮（NO）/鸟苷3',5'-环磷酸（cGMP）途径的激活或抑制性G蛋白（G(i)）的刺激介导的。然而，关于NO/cGMP途径或G(i)蛋白或两者是否介导毒蕈碱激动剂对成年心室肌细胞的负性肌力作用仍存在争议。在本研究中，使用成年大鼠心室肌细胞，毒蕈碱激动剂卡巴胆碱在6分钟内将β-肾上腺素能（异丙肾上腺素）刺激的收缩力（细胞缩短）抑制了82%，并使cGMP水平升高了49%。用可溶性鸟苷酸环化酶抑制剂（1H-[1,2,4]恶二唑并[4,3-a]喹喔啉-1-酮，ODQ）或一氧化氮合酶抑制剂（N(G)-单甲基-L-精氨酸，L-NMMA）预处理心肌细胞30分钟可阻断卡巴胆碱诱导的cGMP水平升高。然而，ODQ或L-NMMA预处理对卡巴胆碱抑制异丙肾上腺素诱导的收缩力均无任何影响。此外，卡巴胆碱并未减弱福斯可林（腺苷酸环化酶的直接激活剂）或8-(4-氯苯硫基)-腺苷3',5'-环磷酸（一种可渗透细胞的cAMP类似物，可激活cAMP依赖性蛋白激酶）诱导的心肌细胞收缩力增加。用G(i)蛋白抑制剂百日咳毒素（PTX，1微克/毫升）预处理心肌细胞18-20小时可消除卡巴胆碱对异丙肾上腺素诱导的收缩力的抑制作用。此外，在用PTX（3微克/100克，腹腔注射）对大鼠进行体内治疗3天后分离的心室肌细胞中，卡巴胆碱的负性肌力作用完全丧失。这些数据表明，毒蕈碱抑制成年大鼠心室肌细胞中β-肾上腺素能受体介导的收缩力增加需要百日咳毒素敏感的G蛋白，而不是NO/cGMP途径。
