INSULIN ACTION ON WHOLE-BODY GLUCOSE-UTILIZATION AND ON MUSCLE GLUCOSE-TRANSPORTER TRANSLOCATION IN MICE

Murine models of insulin resistance and diabetes are versatile and hav e been used to investigate genetic and metabolic disorders. However, t he principal assays to assess insulin action, i.e.,the euglycemic-hype rinsulinemic clamp and subcellular distribution of glucose transporter s, have not been implemented in this species. Here we describe procedu res which allow these methods to be adapted to mice. When normal C57bl /6j mice were infused with graded doses of insulin (1,3,10 or 30 mU/kg /min) during a euglycemic-hyperinsulinemic clamp, the glucose infusion rate necessary to maintain euglycemia increased in a dose-dependent m anner (7.4+/-1.7, 13.1+/-3.6, 24.1+/-2.3 or 34.8+/-7.5 mg/kg/min), res pectively. Hindlimb muscles were isolated and samples of 2-3 g were su bjected to subcellular fractionation finalizing on 25%, 30% and 35% su crose gradients. Fraction F25 (plasma membranes) was enriched in alpha 2 Na+/K+-ATPase and GLUT1 glucose transporters, whereas fraction F35 (intracellular membranes) was enriched in Ca2+-ATPase and GLUT4 glucos e transporters. Following insulin treatment, GLUT4 increased in F25 an d decreased in F35. Insulin treatment had no effect on GLUT1 in F25. H owever, unlike in rat skeletal muscle, GLUT1 was detectable in F35 and its content decreased in this fraction following insulin treatment. T he results demonstrate that whole-body glucose utilization can be asse ssed in mice using euglycemic-hyperinsulinemic clamps and demonstrate how subcellular fractionation procedures can be applied to murine musc le. Murine muscle GLUT4 translocates from an intracellular storage sit e to the plasma membrane in response to insulin. (C) 1994 Academic Pre ss, Inc.