Abstract:

To observe the effects of adiponectin on basal and insulininduced glucose uptake in L6 rat skeletal muscle myoblasts. MethodsWild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.  ResultsIn wildtype L6 cells: the glucose uptake of the adiponectin treatment group was not significantly different from that of the control(P＞0.05).  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(P＞0.05, 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 (P＜0.01, 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(P＜0.01, respectively), and were also significantly higher than those of the lower concentration of insulin treatment group(P＜0.01, 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(P＜0.05,  P＜0.01, respectively). Compared with the adiponectin + lower concentration of insulin group, the glucose uptake of the adiponectin + higher concentration of insulin group was significantly increased(P＜0.05), 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（P＞0.05）nor that of the higher concentration of insulin treatment group（P＞0.05）. Conclusion① 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.

Key words: Adiponectin; Glucose transporter 4; Skeletal muscle c ell; Glucose uptake