Vogt C, Yki-Jarvinen H, Iozzo P, Pipek R, Pendergrass M, Koval J, Ardehali H, Printz R, Granner D, Defronzo R, Mandarino L
Department of Medicine, University of Texas Health Science Center at San Antonio 78284, USA.
J Clin Endocrinol Metab. 1998 Jan;83(1):230-4. doi: 10.1210/jcem.83.1.4476.
The phosphorylation of glucose to glucose-6-phosphate, catalyzed by hexokinase, is the first committed step in glucose uptake into skeletal muscle. Two isoforms of hexokinase, HKI and HKII, are expressed in human skeletal muscle, but only HKII expression is regulated by insulin. HKII messenger RNA, protein, and activity are increased after 4 h of insulin infusion; however, glucose uptake is stimulated much more rapidly, occurring within minutes. Studies in rat muscle suggest that changes in the subcellular distribution of HKII may be an important regulatory factor for glucose uptake. The present studies were undertaken to determine if insulin causes an acute redistribution of HKII activity in human skeletal muscle in vivo. Muscle biopsies (vastus lateralis muscle) were performed before and at the end of 30 min insulin infusion, performed using the euglycemic clamp technique. Muscle biopsies were subfractionated into soluble and particulate fractions to determine if insulin acutely changes the subcellular distribution of HKII. Insulin decreased HKII activity in the soluble fraction from 2.20 +/- 0.31 to 1.40 +/- 0.18 pmoles/(min[chempt]micrograms) and increased HKII activity in the particulate fraction from 3.02 +/- 0.46 to 3.45 +/- 0.46 pmoles/(min[chempt]micrograms) (P < 0.01 for both). These changes in HKII activity were correlated with changes in HKII protein, as determined by immunoblot analysis (r = 0.53, P = 0.05). Insulin had no effect on the subcellular distribution of HKII activity, which was primarily restricted to the soluble fraction. These studies are consistent with the conclusion that, in vivo in human skeletal muscle, insulin changes the subcellular distribution of HKII within 30 min.
己糖激酶催化葡萄糖磷酸化生成葡萄糖-6-磷酸，这是葡萄糖进入骨骼肌的第一个关键步骤。己糖激酶有两种异构体，HKI和HKII，在人类骨骼肌中表达，但只有HKII的表达受胰岛素调节。输注胰岛素4小时后，HKII信使核糖核酸、蛋白质和活性增加；然而，葡萄糖摄取的刺激要快得多，在几分钟内就会发生。对大鼠肌肉的研究表明，HKII亚细胞分布的变化可能是葡萄糖摄取的一个重要调节因素。本研究旨在确定胰岛素是否会在体内导致人类骨骼肌中HKII活性的急性重新分布。在使用正常血糖钳夹技术进行30分钟胰岛素输注之前和结束时，对（股外侧肌）进行肌肉活检。将肌肉活检组织分为可溶性部分和颗粒部分，以确定胰岛素是否会急性改变HKII的亚细胞分布。胰岛素使可溶性部分的HKII活性从2.20±0.31降至1.40±0.18皮摩尔/（分钟·微克），并使颗粒部分的HKII活性从3.02±0.46升至3.45±0.46皮摩尔/（分钟·微克）（两者P均<0.01）。通过免疫印迹分析确定，HKII活性的这些变化与HKII蛋白的变化相关（r = 0.53，P = 0.05）。胰岛素对HKII活性的亚细胞分布没有影响，其主要局限于可溶性部分。这些研究与以下结论一致：在人类骨骼肌体内，胰岛素在30分钟内改变了HKII的亚细胞分布。
