Insulin activation of red blood cell Na+/H+ exchange decreases the affinity of sodium sites.
Insulin activation of red blood cell Na+/H+ exchange decreases the affinity of sodium sites.
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DOI：
10.1038/ki.1994.283
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发表时间：
1994-08
影响因子：
19.6
通讯作者：
Roberto Pontremoli;G. Zerbini;Alicia Rivera;Mitzy Canessa
中科院分区：
文献类型：
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作者：
Roberto Pontremoli;G. Zerbini;Alicia Rivera;Mitzy Canessa
胰岛素激活红细胞Na+/H+交换降低了钠位点的亲和力。我们以前报道过高血压和糖尿病肾病患者红细胞（RBC）中Na+/H+和Na+/Li+交换活性增加。胰岛素受体在人红细胞中的存在使我们研究了这种激素对Na+/H+交换动力学参数的影响，作为确定其作用机制的第一种方法。在不同的时间内，用（w/wo）胰岛素（0至100 μ U/ml）预孵育的酸负载、Na耗尽的红细胞中，通过向外的H+梯度驱动净Na+内流来测量反向转运蛋白的活性。在空腹12小时的正常人红细胞中检测胰岛素对Na+/H+交换H+和Na+活化动力学的影响。胰岛素（50 μ U/ml， 1小时）使vmax从28±6增加到49±8 mmol/l细胞×小时（N = 10, P < 0.0005），使Na+ km从72±10增加到142±19 mM(N = 4, P < 0.05)，但对细胞内H+ km没有影响。胰岛素也增加了ph 7.4（0.34±0.03 ~ 0.45±0.04 mmol/l cell × hr, N = 9, P < 0.005）时Na+/Li+交换的vmax和Na+交换的km（31±3 ~ 76±10 mM, P < 0.0003）。因此，胰岛素可以调节Na+/Li+或Na+/H+交换的Na+位点，而不依赖于H+位点的占用，从而有利于结合的Na+释放到细胞质中。胰岛素刺激Na+/H+交换需要内源性胞浆Ca2+水平。胰岛素对Na+/H+和Na+/Li+交换的动力学效应由冈田酸（300µM）模拟，冈田酸是一种蛋白磷酸酶的抑制剂，能使丝氨酸-苏氨酸残基去磷酸化。与胰岛素一样，冈田酸增加了Na+/H+和Na+/Li+交换的vmax和Na+的km。综上所述，胰岛素刺激Na+/H+反向转运蛋白通过一种新的动力学机制发生，导致Na+的亲和力降低，但对Hi的亲和力不变。基于冈田酸可以模仿胰岛素的作用，我们假设这种激素可能会增加这种反向转运蛋白的丝氨酸-苏氨酸残基的磷酸化状态。
Insulin activation of red blood cell Na+/H+exchange decreases the affinity of sodium sites. We have previously reported increased activity of Na+/H+and Na+/Li+exchanges in red blood cells (RBC) of patients with hypertension and diabetic nephropathy. The presence in human red blood cells (RBC) of insulin receptors has led us to examine the effects of this hormone on the kinetic parameters of Na+/H+exchange as a first approach to define its mechanism of action. The antiporter activity was measured as net Na+influx driven by an outward H+gradient in acid-loaded, Na-depleted RBCs preincubated with or without (w/wo) insulin (0 to 100 µU/ml) for different time periods. The effects of insulin on the H+and Na+activation kinetics of Na+/H+exchange were examined in RBCs of normal subjects fasted for 12 hours. Insulin (50 µU/ml for 1 hr) increased the Vmaxfrom 28 ± 6 to 49 ± 8 mmol/liter cell × hr (N = 10, P < 0.0005) and the Kmfor Na+from 72 ± 10 to 142 ± 19 mM(N = 4, P < 0.05) but did not change the Kmfor intracellular H+. Insulin also increased the Vmaxof Na+/Li+exchange at pHi7.4 (0.34 ± 0.03 to 0.45 ± 0.04 mmol/liter cell × hr, N = 9, P < 0.005) as well as the Kmfor Na+(31 ± 3 to 76 ± 10 mM, P < 0.0003). Therefore, insulin can modulate Na+sites of Na+/Li+or Na+/H+exchanges independent of the occupancy of H+sites to favor the release of bound Na+into the cytoplasm. Insulin stimulation of Na+/H+exchange required endogenous cytosolic Ca2+levels. The kinetic effects of insulin on Na+/H+and Na+/Li+exchanges were imitated by okadaic acid (300 µM), an inhibitor of protein phosphatases which dephosphorylate serine-threonine residues. Okadaic acid increased the Vmaxof Na+/H+and Na+/Li+exchanges and the Kmfor Na+as insulin did. In conclusion, insulin stimulation of the Na+/H+antiporter occurs by a novel kinetic mechanism leading to a decreased affinity for external Na+without changes in the affinity for Hi. On the basis that insulin effects were imitated by okadaic acid, we hypothesize that this hormone may increase the phosphorylated state of serine-threonine residues of this antiporter protein.