胰岛素激活红细胞钠/氢交换会降低钠位点的亲和力。

Insulin activation of red blood cell Na+/H+ exchange decreases the affinity of sodium sites.

作者信息

Pontremoli R, Zerbini G, Rivera A, Canessa M

机构信息

Endocrine-Hypertension Division, Brigham and Women's Hospital, Boston, Massachusetts.

出版信息

Kidney Int. 1994 Aug;46(2):365-75. doi: 10.1038/ki.1994.283.

DOI:10.1038/ki.1994.283

PMID:7967348

Abstract

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 microU/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 microU/ml for 1 hr) increased the Vmax from 28 +/- 6 to 49 +/- 8 mmol/liter cell x hr (N = 10, P < 0.0005) and the Km for Na+ from 72 +/- 10 to 142 +/- 19 mM (N = 4, P < 0.05) but did not change the Km for intracellular H+. Insulin also increased the Vmax of Na+/Li+ exchange at pHi 7.4 (0.34 +/- 0.03 to 0.45 +/- 0.04 mmol/liter cell x hr, N = 9, P < 0.005) as well as the Km for Na+ (31 +/- 3 to 6 +/- 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 microM), an inhibitor of protein phosphatases which dephosphorylate serine-threonine residues. Okadaic acid increased the Vmax of Na+/H+ and Na+/Li+ exchanges and the Km for 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.

摘要

我们之前报道过，高血压和糖尿病肾病患者红细胞（RBC）中Na⁺/H⁺和Na⁺/Li⁺交换活性增强。人类红细胞（RBC）中存在胰岛素受体，这促使我们研究这种激素对Na⁺/H⁺交换动力学参数的影响，以此作为确定其作用机制的首要方法。反向转运体活性通过在酸负荷、Na⁺缺失的红细胞中，由向外的H⁺梯度驱动的净Na⁺内流来测量，这些红细胞在有或无（w/wo）胰岛素（0至100微单位/毫升）的情况下预孵育不同时间段。在禁食12小时的正常受试者的红细胞中，研究了胰岛素对Na⁺/H⁺交换的H⁺和Na⁺激活动力学的影响。胰岛素（50微单位/毫升，作用1小时）使Vmax从28±6增加到49±8毫摩尔/升细胞×小时（N = 10，P < 0.0005），Na⁺的Km从72±10增加到142±19毫摩尔（N = 4，P < 0.05），但细胞内H⁺的Km没有变化。胰岛素还增加了pHi 7.4时Na⁺/Li⁺交换的Vmax（从0.34±0.03增加到0.45±0.04毫摩尔/升细胞×小时，N = 9，P < 0.005）以及Na⁺的Km（从31±3增加到6±10毫摩尔，P < 0.0003）。因此，胰岛素可以独立于H⁺位点的占据情况来调节Na⁺/Li⁺或Na⁺/H⁺交换的Na⁺位点，有利于结合的Na⁺释放到细胞质中。胰岛素对Na⁺/H⁺交换的刺激需要内源性胞质Ca²⁺水平。胰岛素对Na⁺/H⁺和Na⁺/Li⁺交换的动力学影响可被冈田酸（300微摩尔）模拟，冈田酸是一种使丝氨酸 - 苏氨酸残基去磷酸化的蛋白磷酸酶抑制剂。冈田酸像胰岛素一样增加了Na⁺/H⁺和Na⁺/Li⁺交换的Vmax以及Na⁺的Km。总之，胰岛素对Na⁺/H⁺反向转运体的刺激通过一种新的动力学机制发生，导致对外部Na⁺的亲和力降低，而对H⁺的亲和力不变。基于冈田酸可模拟胰岛素的作用，我们推测这种激素可能增加这种反向转运体蛋白丝氨酸 - 苏氨酸残基的磷酸化状态。