Ferreira Ana, Rivera Alicia, Romero José R
Division of Endocrinology, Diabetes and Hypertension, Department of Medicine, Brigham and Women's Hospital and Harvard Medical School, Boston, Massachusetts 02115, USA.
J Cell Physiol. 2004 Jun;199(3):434-40. doi: 10.1002/jcp.10463.
Regulation of cellular Mg(2+) levels by insulin has been shown in various tissues. However, the mechanisms for hormonal regulation of cellular Mg(2+) have not been well described. We studied the effect of insulin on Na(+)/Mg(2+) exchange in normal human cells, measuring Na(+)/Mg(2+) exchange activity as net total Mg(2+) efflux driven by an inward Na(+) gradient in Mg(2+)-loaded red blood cells (RBCs). Na(+)/Mg(2+) exchange was increased significantly by the addition of 2.4 nmol/L of insulin to the flux medium (from 0.60 +/- 0.06 mmol/L cell x h to 0.75 +/- 0.08 mmol/L cell x h [P = 0.0098, n = 44]). A dose-response curve for the effects of insulin on the exchanger activity gave an estimated EC(50) for insulin of 0.95 +/- 0.31 nmol/L and a V(max) of 0.86 +/- 0.12 mmol/L cell x h (n = 7). Kinetics of the Na(+)/Mg(2+) exchange were characterized by measuring its activity as a function of Mg(2+) and Na(+) concentrations. The K(0.5) for cellular Mg(2+) was not affected by incubation with insulin. However, the K(0.5) for extracellular Na(+) decreased from 69.9 +/- 6.3 to 40.3 +/- 8.4 mol/L (n = 5, P = 0.03) in the presence of insulin. We also studied the effect of wortmannin (WT), a PI 3-kinase inhibitor, on activity of the exchanger. WT significantly blocked the insulin-stimulated Na(+)/Mg(2+) activity (n = 6, P = 0.048), with an IC(50) of 0.5 nmol/L. LY294002, another PI 3-kinase inhibitor, likewise blocked the insulin-stimulated activity of the exchanger. Therefore, insulin regulates cellular Mg(2+) metabolism in part via an increase in the affinity for Na(+) of the Na(+)/Mg(2+) exchange and PI 3-kinase activation, suggesting another role for the PI 3-kinase pathway in insulin-mediated cellular events.
胰岛素对细胞镁离子（Mg²⁺）水平的调节已在多种组织中得到证实。然而，激素对细胞镁离子调节的机制尚未得到充分描述。我们研究了胰岛素对正常人细胞中钠/镁离子交换的影响，通过测量镁离子负载的红细胞（RBC）中由内向钠离子梯度驱动的净总镁离子外流来测定钠/镁离子交换活性。向通量介质中添加2.4 nmol/L胰岛素后，钠/镁离子交换显著增加（从0.60±0.06 mmol/L细胞×小时增加到0.75±0.08 mmol/L细胞×小时[P = 0.0098，n = 44]）。胰岛素对交换器活性影响的剂量反应曲线得出胰岛素的估计半数有效浓度（EC₅₀）为0.95±0.31 nmol/L，最大反应速度（Vₘₐₓ）为0.86±0.12 mmol/L细胞×小时（n = 7）。通过测量钠/镁离子交换活性作为镁离子和钠离子浓度的函数来表征其动力学。细胞内镁离子的半最大效应浓度（K₀.₅）不受胰岛素孵育的影响。然而，在存在胰岛素的情况下，细胞外钠离子的K₀.₅从69.9±6.3降至40.3±8.4 mol/L（n = 5，P = 0.03）。我们还研究了磷脂酰肌醇3激酶（PI 3激酶）抑制剂渥曼青霉素（WT）对交换器活性的影响。WT显著阻断了胰岛素刺激的钠/镁离子活性（n = 6，P = 0.048），半数抑制浓度（IC₅₀）为0.5 nmol/L。另一种PI 3激酶抑制剂LY294002同样阻断了交换器的胰岛素刺激活性。因此，胰岛素部分通过增加钠/镁离子交换对钠离子的亲和力和PI 3激酶激活来调节细胞镁离子代谢，提示PI 3激酶途径在胰岛素介导的细胞事件中具有另一个作用。
