Obayashi K, Horie M, Xie L H, Tsuchiya K, Kubota A, Ishida H, Sasayama S
Department of Cardiovascular Medicine, Faculty of Medicine, Kyoto University, Japan.
Circulation. 1997 Jan 7;95(1):197-204. doi: 10.1161/01.cir.95.1.197.
Angiotensin II receptors are reported to be abundant in the guinea pig ventricle; their coupling to adenylate cyclase in the heart, however, remains controversial. Therefore, we investigated the effect of angiotensin II on Cl- conductance activated by cAMP-dependent protein kinase.
After minimizing the contribution of other ionic currents, exposure of single guinea pig ventricular cells to isoproterenol (40 to 50 nmol/L; 36 degrees C) elicited a typical protein kinase A-dependent Cl- conductance. Subsequent application of angiotensin II reduced the isoproterenol-induced conductance with an IC50 of 0.24 +/- 0.08 nmol/L. Angiotensin II also inhibited the Cl- currents, which were activated through stimulation of adenylate cyclase by forskolin and histamine receptors. CV-11974 (1 mumol/L), an antagonist selective for the angiotensin type 1 receptor, prevented the effect of angiotensin II. Angiotensin II did not inhibit the current that had been persistently activated by intracellular GTP gamma S (100 mumol/L), a nonhydrolyzable guanine nucleotide, plus isoproterenol. In addition, prior incubation of myocytes with pertussis toxin prevented the angiotensin II inhibitory action. Cl- conductance, when activated directly by intracellular dialysis with cAMP (1 mmol/L), was not affected by angiotensin II. Radioimmunologic measurement of cellular cAMP in the dissociated myocytes showed that angiotensin II inhibited the isoproterenol-induced increase of cAMP.
Angiotensin II receptors negatively couple to adenylate cyclase via pertussis toxin-sensitive G proteins, thereby inhibiting cardiac protein kinase A-dependent Cl- conductance.
据报道，血管紧张素II受体在豚鼠心室中大量存在；然而，其在心脏中与腺苷酸环化酶的偶联仍存在争议。因此，我们研究了血管紧张素II对由cAMP依赖性蛋白激酶激活的氯离子电导的影响。
在将其他离子电流的影响降至最低后，将单个豚鼠心室细胞暴露于异丙肾上腺素（40至50 nmol/L；36℃）会引发典型的蛋白激酶A依赖性氯离子电导。随后应用血管紧张素II可降低异丙肾上腺素诱导的电导，IC50为0.24±0.08 nmol/L。血管紧张素II还抑制了通过福斯可林和组胺受体刺激腺苷酸环化酶而激活的氯离子电流。CV - 11974（1 μmol/L），一种对血管紧张素1型受体具有选择性的拮抗剂，可阻止血管紧张素II的作用。血管紧张素II不会抑制由细胞内GTPγS（100 μmol/L），一种不可水解的鸟嘌呤核苷酸，加异丙肾上腺素持续激活的电流。此外，预先用百日咳毒素孵育心肌细胞可阻止血管紧张素II的抑制作用。当通过用cAMP（1 mmol/L）进行细胞内透析直接激活时，氯离子电导不受血管紧张素II的影响。对解离的心肌细胞中细胞内cAMP的放射免疫测定表明，血管紧张素II抑制了异丙肾上腺素诱导的cAMP增加。
血管紧张素II受体通过百日咳毒素敏感的G蛋白与腺苷酸环化酶负性偶联，从而抑制心脏蛋白激酶A依赖性氯离子电导。
