Lavoie L, Roy D, Ramlal T, Dombrowski L, Martín-Vasallo P, Marette A, Carpentier J L, Klip A
Division of Cell Biology, Hospital for Sick Children, Toronto, Ontario, Canada.
Am J Physiol. 1996 May;270(5 Pt 1):C1421-9. doi: 10.1152/ajpcell.1996.270.5.C1421.
We have previously shown that an acute insulin treatment induces redistribution of the alpha 2- and beta 1- isoforms of the Na+-K+-ATPase from intracellular membranes to plasma membranes detected on subcellular fractionation of mixed muscles and immunoblotting with isoform-specific antibodies (H. S. Hundal et al. J. Biol. Chem. 267: 5040-5043, 1992). In the present study we give both biochemical and morphological evidence that this insulin effect is operative in muscles composed mostly of oxidative (red) fibers but not in muscles composed mostly of glycolytic (white) fibers. The redistribution of the Na+-K+-ATPase alpha 2- and beta 1-isoforms after insulin injection was detected in membranes isolated from and muscles (soleus, red gastrocnemius, red rectus femoris, and red vastus lateralis) but not in membranes from white muscles (white gastrocnemius, tensor fasciae latae, white rectus femoris, and white vastus lateralis). After insulin injection, the potassium-dependent 3-O-methylfluorescein phosphatase activity of the enzyme was higher by 22% in the plasma membrane-enriched fraction and lower by 15% in the internal membrane fraction isolated from red but not from white muscles. Quantitative immunoelectron microscopy of ultrathin muscle cryosections showed that in vivo insulin stimulation augmented the density of Na+-K+-ATPase alpha 2- and beta 1- isoforms at the plasma membrane of soleus muscle by 80 and 124%, respectively, with no change in white gastrocnemius muscle. The effect of insulin to increase the content of Na+-K+-ATPase alpha 2- and beta 1-subunits in isolated plasma membranes was still observed when glycemia was prevented from dropping by using hyperinsulinemic-euglycemic clamps. We conclude that the insulin-induced redistribution of the alpha 2- and beta 1-isoforms of the Na+-K+-ATPase from an intracellular pool to the plasma membrane in restricted to oxidative fiber-type skeletal muscles. This may be related to the selective expression of beta 1-subunits in these fibers and implies that the beta 2-subunit, typical of glycolytic muscles, does not sustain translocation of alpha 2 beta 2-complexes.
我们之前已经表明，急性胰岛素处理可诱导钠钾ATP酶的α2和β1同工型从细胞内膜重新分布到质膜，这一现象通过混合肌肉的亚细胞分级分离以及用同工型特异性抗体进行免疫印迹得以检测（H. S. Hundal等人，《生物化学杂志》267: 5040 - 5043, 1992）。在本研究中，我们提供了生化和形态学证据，表明这种胰岛素效应在主要由氧化型（红色）纤维组成的肌肉中起作用，而在主要由糖酵解型（白色）纤维组成的肌肉中则不起作用。胰岛素注射后，在从红色肌肉（比目鱼肌、红色腓肠肌、红色股直肌和红色股外侧肌）分离的膜中检测到钠钾ATP酶α2和β1同工型的重新分布，但在白色肌肉（白色腓肠肌、阔筋膜张肌、白色股直肌和白色股外侧肌）的膜中未检测到。胰岛素注射后，在从红色而非白色肌肉分离的富含质膜的部分中，该酶的钾依赖性3 - O - 甲基荧光素磷酸酶活性高22%，而在内膜部分中低15%。超薄肌肉冷冻切片的定量免疫电子显微镜显示，体内胰岛素刺激使比目鱼肌质膜上钠钾ATP酶α2和β1同工型的密度分别增加80%和124%，而白色腓肠肌无变化。当使用高胰岛素 - 正常血糖钳制防止血糖下降时，仍可观察到胰岛素增加分离的质膜中钠钾ATP酶α2和β1亚基含量的效应。我们得出结论，胰岛素诱导的钠钾ATP酶α2和β1同工型从细胞内池到质膜的重新分布仅限于氧化型纤维类型的骨骼肌。这可能与这些纤维中β1亚基的选择性表达有关，意味着糖酵解型肌肉典型的β2亚基不支持α2β2复合物的转运。
