Effects of angiotensin II on insulin signal transduction in myoblasts of L6 rats

Objective To study the effects of angiotensin Ⅱ (AngⅡ) on insulin signal transduction pathway in skeletal myoblast of L6 rats,and further to explore the possible mechanism of AngⅡ on glucose utilization.Methods Myoblast cells of L6 rats were cultured and induced to differentiate.They were divided into 4 groups according to different treatment by AngⅡ or JAK2-PKA inhibitor H89:normal control group ( NC group),insulin group,insulin + AngⅡ group and insulin + AngⅡ + H89 group.Expression of IRS1 and GLUT4 mRNA was detected by RT-PCR.Expression of IRS1,Ptyr-IRS1 and GLUT4 (total and membrane protein) were detected by Western blot.Results The difference of GLUT4 mRNA expression in the 4 groups detected by RT-PCR had no statistical significance(P ＞ 0.05).The difference of IRS1 mRNA expression among the latter 3 groups had no statistical significance(P ＞ 0.05),however,IRS1 expression in the latter 3 groups was higher than that in NC group(P ＜ 0.05).Western blot results showed expression of IRS1,Ptyr-IRS1 and GLUT4 (membrane protein)was higher in the latter 3 groups than in NC group(P ＜0.05).The difference of IRS1 expression among the latter 3 groups(P ＞ 0.05 ) and GLUT4 (total protein) expression among the 4 groups had no statistical significance (P ＞ 0.05).The expression of of ptyr-IRS1 and GLUT4 membrane protein in Ins + AngⅡ + H89 group was much higher than that in Ins + AngⅡ group,and lower than that in insulin group(P ＜0.05).Conclusion AngⅡ inhibits IRS1's tyrosine phosphorylation and GLUT4's transfer from cytoplasm to plasma membrane in skeletal muscle cells through JAK2-PKA signaling pathway,and therefore induces insulin resistance. Key words: L6;  Angiotensin Ⅱ; H89;  IRS1;  GLUT4