Insulin-stimulated insulin receptor substrate-2–associated phosphatidylinositol 3–kinase activity is enhanced in human skeletal muscle after exercise

Abstract

Exercise increases skeletal muscle insulin action but the underlying mechanisms mediating this are equivocal. In mouse skeletal muscle, prior exercise enhances insulin-stimulated insulin receptor substrate-2 (IRS-2) signaling ( Diabetes 2002;51:479-83), but it is unknown if this also occurs in humans. Hyperinsulinemic-euglycemic clamps were performed on 7 untrained males at rest and immediately after 60 minutes of cycling exercise at ∼75% V o 2peak. Muscle biopsies were obtained at basal, immediately after exercise, and at 30 and 120 minutes of hyperinsulinemia. Insulin infusion increased ( P < .05) insulin receptor tyrosine phosphorylation similarly in both the rest and exercise trials. Under resting conditions, insulin infusion resulted in a small, but non–statistically significant increase in IRS-2–associated phosphatidylinositol 3 (PI 3)–kinase activity over basal levels. Exercise per se decreased ( P < .05) IRS-2–associated PI 3–kinase activity. After exercise, insulin-stimulated IRS-2–associated PI 3–kinase activity tended to increase at 30 minutes and further increased ( P < .05) at 120 minutes when compared with the resting trial. Insulin increased ( P < .05) Akt Ser 473 and GSK-3 α/ β Ser 21/Ser 9 phosphorylation in both trials, with the response tending to be higher in the exercise trial. In conclusion, in the immediate period after an acute bout of exercise, insulin-stimulated IRS-2 signaling is enhanced in human skeletal muscle.