Cheung J Y, Constantine J M, Bonventre J V
Am J Physiol. 1987 Feb;252(2 Pt 1):C163-72. doi: 10.1152/ajpcell.1987.252.2.C163.
The role of cytosolic free Ca2+ concentration, [Cai], in mediating insulin's stimulatory effect on glucose transport was investigated in isolated Ca2+-tolerant rat ventricular cells. Approximately 98% of glucose transport in isolated myocytes was inhibited by phloretin. Insulin-accelerated glucose transport by 50-115% over basal transport rate. Removal of extracellular Ca2+ had no effect on either the basal transport rate or insulin's stimulatory action, indicating that extracellular Ca2+ was not necessary for insulin's effect to be manifest. Addition of A23187 had no effect on glucose transport rate. Under basal conditions, [Cai] was 167 +/- 12 nM as measured by fura-2 fluorescence and 239 +/- 22 nM by null-point titration with arsenazo III. Loading cells with fura-2 did not affect basal glucose transport rates. In addition, the stimulatory effect of insulin on glucose transport was preserved in fura-2 loaded cells. In paired experiments, insulin did not increase [Cai] as measured by fura-2 fluorescence or null-point titration despite acceleration of glucose transport. In contrast, addition of KCl (40 mM) increased [Cai] from 168 +/- 30 to 287 +/- 51 nM and resulted in 50% reduction in glucose transport rate. In other experiments designed to control for the hyperosmolar effects of KCl, NaCl (40 mM) caused no change in [Cai] but also inhibited glucose transport rate by 50%. We conclude that an elevation in [Cai] is unlikely to be the intracellular signal mediating insulin's effect on glucose transport since insulin's stimulatory effect was not reduced by Ca2+ -free media, insulin had no detectable effect on [Cai], and elevation of [Cai] by KCl did not result in stimulation of glucose transport.
在分离的耐钙大鼠心室细胞中研究了胞质游离钙离子浓度（[Cai]）在介导胰岛素对葡萄糖转运的刺激作用中的作用。在分离的心肌细胞中，约98%的葡萄糖转运被根皮素抑制。胰岛素使葡萄糖转运速度比基础转运速度加快50 - 115%。去除细胞外钙离子对基础转运速度或胰岛素的刺激作用均无影响，这表明细胞外钙离子对于胰岛素作用的显现并非必需。添加A23187对葡萄糖转运速度无影响。在基础条件下，通过fura - 2荧光测定的[Cai]为167±12 nM，通过用偶氮胂III进行零点滴定测定为239±22 nM。用fura - 2加载细胞不影响基础葡萄糖转运速度。此外，在加载fura - 2的细胞中，胰岛素对葡萄糖转运的刺激作用得以保留。在配对实验中，尽管葡萄糖转运加速，但通过fura - 2荧光或零点滴定测定，胰岛素并未增加[Cai]。相反，添加KCl（40 mM）使[Cai]从168±30 nM增加到287±51 nM，并导致葡萄糖转运速度降低50%。在其他旨在控制KCl高渗效应的实验中，NaCl（40 mM）未引起[Cai]变化，但也使葡萄糖转运速度降低了50%。我们得出结论，[Cai]升高不太可能是介导胰岛素对葡萄糖转运作用的细胞内信号，因为无钙培养基并未降低胰岛素的刺激作用，胰岛素对[Cai]无可检测到的影响，并且KCl引起的[Cai]升高并未导致葡萄糖转运的刺激。
