Na+/Mg2+ exchange is functionally coupled to the insulin receptor.
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.
Ferreira
Ana
A
Division of Endocrinology, Diabetes and Hypertension, Department of Medicine, Brigham and Women's Hospital and Harvard Medical School, Boston, Massachusetts 02115, USA.
Rivera
Alicia
A
Romero
José R
JR
D017920:Antiporters / Q000187:drug effects / Q000502:physiology*; D004305:Dose-Response Relationship, Drug; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004912:Erythrocytes / Q000187:drug effects / Q000378:metabolism; D006801:Humans; D007328:Insulin / Q000378:metabolism* / Q000494:pharmacology; D008274:Magnesium / Q000378:metabolism*; D000081082:Phosphoinositide-3 Kinase Inhibitors; D011972:Receptor, Insulin / Q000502:physiology*; D012964:Sodium / Q000378:metabolism*
D017920:Antiporters; D004791:Enzyme Inhibitors; D007328:Insulin; D000081082:Phosphoinositide-3 Kinase Inhibitors; C046250:sodium-magnesium antiporter; D012964:Sodium; D011972:Receptor, Insulin; D008274:Magnesium