ALPHA-ADRENERGIC STIMULATION IN MYOCARDIAL CELLS

我们之前已经证明，α1的正性变力作用- 肾上腺素能受体(α1-AR)的刺激，至少部分是由于 蛋白激酶增强肌丝对钙离子的反应性 C(PKC)依赖的Na+/H+交换的激活和 胞液pH(Phi)。我们还研究了α1-AR的作用 收缩、血管紧张素转换酶和肌丝的α1A和α1B亚型 分离心肌细胞对钙离子的反应。α1a-AR刺激 (苯肾上腺素、纳多洛尔和α1B-AR失活 氯乙基可乐定)收缩增加，蔡氏瞬间波幅 肌丝对钙离子的反应。相比之下，Alpha1B-AR刺激 (苯肾上腺素、纳多洛尔和α1A-WB-4101的阻滞剂)减少 收缩、血管紧张素转换酶瞬时波幅和下调α1 A-AR 增强肌丝对钙离子的反应。在附加内容中 实验中我们考察了α1a和α1B-AR的作用 α1B-AR对pH的刺激及其对PKC的依赖 PHI和心肌细胞收缩。在HCO3-/CO2中- 缓冲生理盐水，α1a可提高胞浆pH。与之形成对比的是字母1B 胞液pH降低，这种影响在无HCO3/CO2的情况下持续存在 解决方案。Alpha1B介导的胞浆酸化被取消 星形孢菌素，一种蛋白激酶C抑制剂，通过蛋白激酶C 长期暴露于4β-佛波醇12-肉豆蔻酸酯的下调作用 13-乙酸酯。抽动幅度的变化与胞浆中的变化平行 PH是由于α1a或α1B肾上腺素能受体刺激所致。我们的 结果表明，α1A-AR和α-1B-AR的作用相反 分离的心肌细胞的PHI动态平衡。

We have previously shown that the positive inotropic action of alpha1- adrenoceptor (alpha1-AR) stimulation, at least in part is due to an enhanced myofilament responsiveness to Ca2+ mediated by protein kinase C (PKC)-dependent activation of Na+/H+ exchange and an increase in cytosolic pH (pHi). We have also examined the effect of alpha1-AR subtypes, alpha1A and alpha1B on contraction, Cai and myofilament response to Ca2+ of isolated myocardial cells. alpha1A-AR stimulation (phenylephrine, nadolol and alpha1B-AR inactivation with chloroethylclonidine) increased contraction, Cai transient amplitude and myofilament response to Ca2+. In contrast alpha1B-AR stimulation (phenylephrine, nadolol and alpha1A-blockade with WB-4101) decreased contraction, Cai transient amplitude and downregulated the alpha1A-AR effect to increase myofilament response to Ca2+. In additional experiments we have examined the effect of alpha1A- and alpha1B-AR stimulation on pHi and the PKC-dependence of the alpha1B-AR effect on pHi and contraction of isolated myocardial cells. In HCO3-/CO2- buffered saline, alpha1A increased cytosolic pH. In contrast alpha1B decreased cytosolic pH and this effect persisted in HCO3-/CO2-free solution. alpha1B-mediated cytosolic acidification was abolished by staurosporine, a protein kinase C inhibitor, and by protein kinase C down-regulation with prolonged exposure to 4beta-phorbol 12-myristate 13-acetate. Changes in twitch amplitude paralleled those in cytosolic pH due either to alpha1A- or alpha1B- adrenoceptor stimulation. Our results show that alpha1A-AR and alpha-1B-AR have opposite effects on pHi homeostasis of isolated myocardial cells.