Malbon C C, Gilman H R, Fain J N
Biochem J. 1980 Jun 15;188(3):593-9. doi: 10.1042/bj1880593.
Activation of glycogen phosphorylase by hormones was examined in hepatocytes isolated from euthyroid and hypothyroid female rats and incubated by Ca2+-free buffer containing 1 mM-EGTA. Basal glycogen phosphorylase activity was decreased in Ca2+-free buffer. However, the activation of hepatocyte glycogen phosphorylase, in the absence of extracellular Ca2+, in response to adrenaline, glucagon or phenylephrine was slightly lower, whereas that by vasopressin was abolished. The activation of glycogen phosphorylase by phenylephrine, adrenaline or isoproterenol (isoprenaline) in hepatocytes from euthyroid rats incubated in the absence of Ca2+ was not accompanied by any detectable increase in total cyclic AMP. The log-dose/response curves for activation of phosphorylase by phenylephrine or low concentrations of adrenaline were the same in hepatocytes from hypothyroid as compared wit euthyroid rats, whereas the response to isoproterenol was greater in hepatocytes from hypothyroid rats. However, the increases in total cyclic AMP accumulation caused by adrenaline or isoproterenol were greater in hepatocytes from hypothyroid rats than in hepatocytes from euthyroid rats. The increases in cyclic AMP accumulation caused by adrenaline or isoproterenol in Ca2+-depleted hepatocytes from hypothyroid rats were blocked by propranolol, a beta-adrenergic antagonist. In contrast, propranolol was only partially effective asan inhibitor of the activation of glycogen phosphorylase by phenylephrine or adrenaline in hepatocytes from hypothyroid rats and ineffective on phosphorylase activation in cells from euthyroid rats. These data indicate that the alpha-adrenergic activation of glycogen phosphorylase is not affected by the absence of extracellular Ca2+, and the extent to which total cyclic AMP was increased by adrenergic amines did not correlate with glycogen phosphorylase activation.
在从正常甲状腺和甲状腺功能减退的雌性大鼠分离出的肝细胞中，研究了激素对糖原磷酸化酶的激活作用，并将其置于含有1 mM乙二醇双四乙酸（EGTA）的无钙缓冲液中孵育。在无钙缓冲液中，基础糖原磷酸化酶活性降低。然而，在没有细胞外钙的情况下，肝细胞糖原磷酸化酶对肾上腺素、胰高血糖素或去氧肾上腺素的激活作用略低，而对血管加压素的激活作用则被消除。在无钙条件下孵育的正常甲状腺大鼠肝细胞中，去氧肾上腺素、肾上腺素或异丙肾上腺素（喘息定）对糖原磷酸化酶的激活作用并未伴随总环磷酸腺苷（cAMP）的任何可检测到的增加。与正常甲状腺大鼠相比，甲状腺功能减退大鼠肝细胞中去氧肾上腺素或低浓度肾上腺素激活磷酸化酶的对数剂量/反应曲线相同，而甲状腺功能减退大鼠肝细胞对异丙肾上腺素的反应更大。然而，甲状腺功能减退大鼠肝细胞中肾上腺素或异丙肾上腺素引起的总环磷酸腺苷积累的增加比正常甲状腺大鼠肝细胞中的更大。甲状腺功能减退大鼠无钙肝细胞中肾上腺素或异丙肾上腺素引起的环磷酸腺苷积累的增加被β-肾上腺素能拮抗剂普萘洛尔阻断。相比之下，普萘洛尔仅部分有效地抑制甲状腺功能减退大鼠肝细胞中去氧肾上腺素或肾上腺素对糖原磷酸化酶的激活作用，而对正常甲状腺大鼠细胞中磷酸化酶的激活作用无效。这些数据表明，糖原磷酸化酶的α-肾上腺素能激活不受细胞外钙缺乏的影响，并且肾上腺素能胺使总环磷酸腺苷增加的程度与糖原磷酸化酶的激活无关。
