Effects of insulin and insulin-like growth factor-1 on intracellular magnesium of platelets

Magnesium (Mg2+), the second most abundant intracellular cation, is a critical cofactor in numerous enzymatic reactions. After stimulation of platelets with insulin and insulin-like growth factor-1 (IGF-1), we examined changes in cytosolic free Mg2+ ([Mg2+]i) by using fluorescent probe magfura-2. Basal [Mg2+]i in platelets was 614 +/- 1 microM (mean +/- SEM, n = 60). Insulin and IGF-1 induced an immediate rise of [Mg2+]i in a dose-dependent manner. After stimulation of platelets with 100 microU/mL of insulin for 60 s, [Mg2+]i was significantly elevated to 1270 +/- 53 microM (n = 30, P < 0.05), i.e., 82 +/- 5% over resting [Mg2+]i. IGF-1 (5 micrograms/mL) also increased [Mg2+]i (1020 +/- 53 microM, 69 +/- 10% over resting [Mg2+]i, n = 30). In the medium containing choline instead of sodium or the medium without potassium, an elevation of [Mg2+]i with addition of insulin/IGF-1 was moderately suppressed. Amiloride, a Na+-H+ antiport inhibitor, did not block the insulin/IGF-1 effect. Insulin/ IGF-1 translocates Mg2+ from the extracellular space to intracellular space and these effects are affected by external sodium and potassium.