Effects of adiponectin on glucose uptake in L6 rat skeletal muscle cells.

Objective To observe the effects of adiponectin on basal and insulin-induced glucose uptake in L6 rat skeletal muscle myoblasts.Methods Wild-type L6 cells were divided into 3 groups:the adiponectin treatment group(stimulation with adiponectin for 30 min),the insulin treatment group(stimulation with 10 nmol/L insulin for 20 min)and the control group.After treatments,the glucose uptake of each group was determined.L6 cells stably expressing GLUT4(Glucose transporter 4)were divided into 6 groups:the control group,the adiponectin treatment group(stimulation with adiponectin for 30 min),the lower concentration of insulin group(stimulation with 0.1 nmol/L insulin for 20 min),the higher concentration of insulin group(stimulation with 10 nmol/Linsulin for 20 min),the adiponectin+lower concentration of insulin group(pre-treatment with adiponectin for 30 min,then stimulation with 0.1 nmol/L insulin for 20 min),and the adiponectin+higher concentration of insulin group(pre-treatment with adiponectin for 30 min,then stimulation with 10 nmol/L insulin for 20 min).After treatments,glucose uptake and plasma membrane GLUT4 content were determined.Results In wild-type L6 cells:the glucose uptake of the adiponectin treatment group was not significantly different from that of the control(P0.05).In L6-GLUT4 cells:① Without insulin stimulation,the glucose uptake and the plasma membrane GLUT4 content of the adiponectin treatment group were not significantly different from those of the control(P0.05,respectively).② The glucose uptake and the plasma membrane GLUT4 content of the lower concentration of insulin treatment group were both significantly higher than those of the control(P0.01,respectively).With lower concentration of insulin treatment,the glucose uptake and the plasma membrane GLUT4 content of cells pre-treated with adiponectin were both higher than those of the adiponectin treatment group(P0.01,respectively),and were also significantly higher than those of the lower concentration of insulin treatment group(P0.01,respectively).③ With higher concentration of insulin treatment,the glucose uptake and the plasma membrane GLUT4 content were further increased when compared with those with lower concentration of insulin treatment(P0.05,P0.01,respectively).Compared with the adiponectin + lower concentration of insulin group,the glucose uptake of the adiponectin + higher concentration of insulin group was significantly increased(P0.05),and was also higher than that of the higher concentration of insulin group,however the plasma membrane GLUT4 content of the adiponectin + higher concentration of insulin group was neither significantly different from that of the adiponectin + lower concentration of insulin group(P0.05)nor that of the higher concentration of insulin treatment group(P0.05).Conclusion ① Adiponectin has no effect on basal glucose uptake of L6 rat skeletal muscle cells.② Adiponectin alone is not sufficient to cause GLUT4 plasma membrane translocation and glucose uptake in L6 rat skeletal muscle cells.③ Adiponectin enhances insulin-induced glucose uptake in skeletal muscle cells possibly by sensitizing insulin-induced GLUT4 plasma membrane translocation and by increasing the efficacy of GLUT4 mediated glucose transportation.