Jouneaux C, Mallat A, Serradeil-Le Gal C, Goldsmith P, Hanoune J, Lotersztajn S
Unité Institut National de la Santé et de la Recherche Médicale, Hôpital Henri Mondor, Créteil, France.
J Biol Chem. 1994 Jan 21;269(3):1845-51.
We have demonstrated in liver from male rats that both endothelin A (ETA) and ETB receptors coexist in equal proportion and that ETA receptors mediate a calcium-dependent activation of glycogenolysis. We describe here a sex difference in endothelin action in hepatocytes because, in female rats, 80% of the ET receptors are of ETB type and, accordingly, activation of glycogenolysis is an ETB-mediated process (EC50 = 0.03 pM). ET-1 stimulation of glycogenolysis in female rats was consecutive to activation of phosphatidylinositol 4,5-bisphosphate hydrolysis (EC50 = 0.03 pM) and to inhibition of the calcium extrusion pump (IC50 = 0.03 pM) in plasma membranes, with ET-1 approximately sarafotoxin S6C approximately ET-3. Endothelin regulation of each effector was potentiated by GTP gamma S. ET-1 did not stimulate adenylyl cyclase activity. To identify the nature of the guanine nucleotide regulatory proteins (G protein(s)) coupling ETB receptors to each effector, we used antibodies against the COOH terminus of different G protein alpha subunits. Antibodies reactive with Gs alpha (RM) blocked ET-1 inhibition of the calcium pump, while they did not affect ET-1 stimulation of phospholipase C. Antibodies reactive with Gq alpha (QL) dose-dependently antagonized stimulation of phospholipase C by ET-1 and vasopressin, without affecting ET-1 inhibition of the calcium pump. Antibodies reactive with Gi1 alpha/Gi2 alpha (AS) had no effect on either system. We conclude that the calcium signal provoked by endothelins in hepatocyte is not only consecutive to activation of phospholipase C but also to inhibition of the plasma membrane calcium pump, each effector being coupled to ETB receptors by different G proteins, Gq, and Gs.
我们已在雄性大鼠肝脏中证实，内皮素A（ETA）受体和ETB受体以相等比例共存，且ETA受体介导糖原分解的钙依赖性激活。我们在此描述了内皮素在肝细胞中作用的性别差异，因为在雌性大鼠中，80%的ET受体为ETB型，因此，糖原分解的激活是一个由ETB介导的过程（半数有效浓度=0.03 pM）。在雌性大鼠中，ET-1刺激糖原分解是在激活磷脂酰肌醇4,5-二磷酸水解（半数有效浓度=0.03 pM）以及抑制质膜钙泵（半数抑制浓度=0.03 pM）之后发生的，ET-1与萨拉毒素S6C及ET-3的作用大致相当。GTPγS可增强内皮素对每种效应器的调节作用。ET-1不刺激腺苷酸环化酶活性。为确定将ETB受体与每种效应器偶联的鸟嘌呤核苷酸调节蛋白（G蛋白）的性质，我们使用了针对不同G蛋白α亚基COOH末端的抗体。与Gsα（RM）反应的抗体可阻断ET-1对钙泵的抑制作用，但不影响ET-1对磷脂酶C的刺激作用。与Gqα（QL）反应的抗体可剂量依赖性地拮抗ET-1和血管加压素对磷脂酶C的刺激作用，而不影响ET-1对钙泵的抑制作用。与Gi1α/Gi2α（AS）反应的抗体对这两个系统均无影响。我们得出结论，内皮素在肝细胞中引发的钙信号不仅是磷脂酶C激活之后的结果，也是质膜钙泵抑制之后的结果，每种效应器通过不同的G蛋白Gq和Gs与ETB受体偶联。
