Matsuda T, Murata Y, Kawamura N, Hayashi M, Tamada K, Takuma K, Maeda S, Baba A
Department of Pharmacology, Faculty of Pharmaceutical Sciences, Osaka University, Japan.
Arch Biochem Biophys. 1993 Nov 15;307(1):175-82. doi: 10.1006/abbi.1993.1576.
Treatment of cultured rat astrocytes with insulin increased (Na+ + K+)-ATPase activity expressed per protein or DNA by 1.6- to 2.1-fold, but did not affect Mg(2+)-ATPase and adenylate cyclase activities. Insulin treatment increased protein and DNA contents under the conditions, while it did not cause morphological differentiation as determined by a microscopic inspection. Insulin-like growth factor-I (IGF-I) had a similar effect on the enzyme activity in astrocytes: the effect of insulin was observed at supraphysiological concentrations, while that of IGF-I was observed at physiological concentrations. Insulin and IGF-I both stimulated DNA synthesis at the concentrations that caused an increase in enzyme activity. The effect was blocked by tyrosine kinase inhibitors such as genistein and herbimycin A and by cycloheximide. Western blot analysis showed that alpha 1 and alpha 2 isoforms of (Na+ + K+)-ATPase were present in cultured astrocytes and that insulin and IGF-I increased the content of the alpha 1 isoform but did not that of the alpha 2 isoform. Two components of ouabain inhibition were observed in the enzyme purified partially from cultured astrocytes, and treatment of the cells with IGF-I increased the ratio of the low-affinity component of the inhibition, indicating a selective increase in the activity of the alpha 1 isoform. These results indicate that insulin increases (Na+ + K+)-ATPase activity through an activation of IGF-I receptors and the increase is due to the selective induction of the alpha 1 isoform in cultured astrocytes.
用胰岛素处理培养的大鼠星形胶质细胞，可使每单位蛋白质或DNA所表达的（Na⁺ + K⁺）-ATP酶活性增加1.6至2.1倍，但不影响Mg²⁺-ATP酶和腺苷酸环化酶的活性。在这些条件下，胰岛素处理可增加蛋白质和DNA含量，而通过显微镜检查确定其未引起形态分化。胰岛素样生长因子-I（IGF-I）对星形胶质细胞中的酶活性有类似作用：胰岛素在超生理浓度下观察到其作用，而IGF-I在生理浓度下观察到其作用。胰岛素和IGF-I在引起酶活性增加的浓度下均刺激DNA合成。该作用被酪氨酸激酶抑制剂如染料木黄酮和赫曲霉素A以及环己酰亚胺阻断。蛋白质印迹分析表明，培养的星形胶质细胞中存在（Na⁺ + K⁺）-ATP酶的α1和α2同工型，胰岛素和IGF-I增加了α1同工型的含量，但未增加α2同工型的含量。在从培养的星形胶质细胞中部分纯化的酶中观察到哇巴因抑制的两个组分，用IGF-I处理细胞增加了抑制的低亲和力组分的比例，表明α1同工型的活性选择性增加。这些结果表明，胰岛素通过激活IGF-I受体增加（Na⁺ + K⁺）-ATP酶活性，并且这种增加是由于培养的星形胶质细胞中α1同工型的选择性诱导所致。
