Morris N J, Young P, Houslay M D
Department of Biochemistry, University of Glasgow, U.K.
Biochem J. 1995 Jun 1;308 ( Pt 2)(Pt 2):693-6. doi: 10.1042/bj3080693.
Challenge of intact hepatocytes with insulin reduced the level of phosphorylated alpha-Gi-2 found under basal (resting) conditions. At maximally effective concentrations of insulin the steady-state labelling of alpha-Gi-2 was reduced by approximately 21%. Insulin achieved this in a time- and dose-dependent fashion, exhibiting an IC50 value of 109 +/- 22 pM. The increased labelling of alpha-Gi-2 seen after challenge of cells with phorbol 12-myristate 13-acetate was also attenuated by insulin. Treatment of hepatocytes with the protein phosphatase inhibitor okadaic acid increased the labelling of alpha-Gi-2 in a fashion which was insensitive to the action of insulin. It is suggested that insulin may reduce the level of phosphorylation of alpha-Gi-2 by stimulating intracellular protein phosphatase activity and that this action may offer a molecular explanation for the ability of insulin to inhibit adenylate cyclase activity in hepatocytes by increasing the level of non-phosphorylated alpha-Gi-2.
用胰岛素刺激完整的肝细胞会降低在基础（静息）状态下发现的磷酸化α-Gi-2的水平。在胰岛素的最大有效浓度下，α-Gi-2的稳态标记减少了约21%。胰岛素以时间和剂量依赖性方式实现了这一点，其IC50值为109±22 pM。在用佛波醇12-肉豆蔻酸酯13-乙酸酯刺激细胞后观察到的α-Gi-2标记增加也被胰岛素减弱。用蛋白磷酸酶抑制剂冈田酸处理肝细胞会以一种对胰岛素作用不敏感的方式增加α-Gi-2的标记。有人提出，胰岛素可能通过刺激细胞内蛋白磷酸酶活性来降低α-Gi-2的磷酸化水平，并且这种作用可能为胰岛素通过增加非磷酸化α-Gi-2的水平来抑制肝细胞中腺苷酸环化酶活性的能力提供分子解释。
