Jang Y J, Ryu H J, Choi Y O, Kim C, Leem C H, Park C S
Department of Physiology and the Institute for Calcium Research, University of Ulsan College of Medicine, Songpagu, Seoul, Korea.
Metabolism. 2002 Jul;51(7):912-8. doi: 10.1053/meta.2002.33351.
It has been postulated that sustained high levels of intracellular calcium concentration (Ca(2+)) in the insulin target cells may cause insulin resistance. We evaluated this hypothesis by examining the effect of an intracellular Ca(2+) chelator, 5,5'-dimethyl derivative of bis (o-aminophenoxy) ethane-N,N,N',N' tetraacetic acetoxymethyl ester (dimethyl-BAPTA/AM), on insulin resistance. Insulin resistance was induced in rats by feeding a high-fat diet for 3 to 4 weeks. The whole body insulin sensitivity was determined by the steady state glucose infusion rate (GIR) under euglycemic hyperinsulinemic (6 mU x kg(-1) x min(-1)) clamps. Compared with control rats, the high-fat diet (HFD) fed rats showed significantly lower GIR (12.2 +/- 0.7 v 20.2 +/- 0.9 mg x kg(-1) x min(-1); P <.01). In the HFD rats, an intravenous injection of dimethyl-BAPTA/AM (6 mg/kg) 90 minutes before the clamps significantly increased GIR to 16.3 +/- 0.9 mg x kg(-1) x min(-1) (P <.02), reversing insulin resistance by about 50%; but this intervention had no effect in the controls. This increase in GIR by dimethyl-BAPTA/AM was observed without an increase in femoral artery blood flow, indicating that the chelator increased GIR directly through improving cellular responsiveness to insulin. The stimulatory effect of insulin on 2-deoxy glucose (2-DG) uptake by the isolated epididymal adipocytes was reduced by 35% in the HFD rats compared with the control rats (P <.01). Pretreatment of the HFD rats with dimethyl-BAPTA/AM restored 2-DG uptake to the level in the control rats. The direct measurement of Ca(2+) using fura-2/AM in isolated adipocytes showed that basal Ca(2+) was significantly higher in the HFD rats than in the control rats (145 +/- 11 v 112 +/- 9 nmol/L; P <.05). An injection of dimethyl-BAPTA/AM in the HFD rats lowered Ca(2+) to 127 +/- 11 nmol/L, which did not differ from the level in the control rats (P >.2). The present study clearly demonstrates that an injection of intracellular Ca(2+) chelator in the HFD rats reverses insulin resistance, as well as normalizes elevated Ca(2+) in the insulin target cells. The results strongly support that sustained high levels of Ca(2+) in the insulin target cells may play an important role in insulin resistance, at least in the HFD rats.
据推测，胰岛素靶细胞内持续高水平的钙浓度（Ca(2+)）可能会导致胰岛素抵抗。我们通过研究细胞内钙螯合剂双（邻氨基苯氧基）乙烷-N,N,N',N' - 四乙酸乙酰氧甲酯的5,5'-二甲基衍生物（二甲基 - BAPTA/AM）对胰岛素抵抗的影响来评估这一假设。通过给大鼠喂食高脂饮食3至4周诱导胰岛素抵抗。通过在正常血糖高胰岛素血症（6 mU x kg(-1) x min(-1)）钳夹状态下的稳态葡萄糖输注率（GIR）来测定全身胰岛素敏感性。与对照大鼠相比，高脂饮食（HFD）喂养的大鼠显示GIR显著降低（12.2 +/- 0.7对20.2 +/- 0.9 mg x kg(-1) x min(-1)；P <.01）。在HFD大鼠中，在钳夹前90分钟静脉注射二甲基 - BAPTA/AM（6 mg/kg）可使GIR显著增加至16.3 +/- 0.9 mg x kg(-1) x min(-1)（P <.02），使胰岛素抵抗逆转约50%；但该干预对对照组无影响。观察到二甲基 - BAPTA/AM使GIR增加，而股动脉血流量未增加，这表明螯合剂通过改善细胞对胰岛素的反应性直接增加了GIR。与对照大鼠相比，HFD大鼠中胰岛素对分离的附睾脂肪细胞摄取2 - 脱氧葡萄糖（2 - DG）的刺激作用降低了35%（P <.01）。用二甲基 - BAPTA/AM预处理HFD大鼠可使2 - DG摄取恢复到对照大鼠的水平。使用fura - 2/AM对分离的脂肪细胞进行Ca(2+)的直接测量显示，HFD大鼠的基础Ca(2+)显著高于对照大鼠（145 +/- 11对出112 +/- nmol/L；P <.05）。给HFD大鼠注射二甲基 - BAPTA/AM可使Ca(2+)降至127 +/- 11 nmol/L，与对照大鼠的水平无差异（P >.2）。本研究清楚地表明，给HFD大鼠注射细胞内钙螯合剂可逆转胰岛素抵抗，并使胰岛素靶细胞中升高的Ca(2+)恢复正常。结果有力地支持了胰岛素靶细胞内持续高水平的Ca(2+)可能在胰岛素抵抗中起重要作用，至少在HFD大鼠中如此。
