Effects of Brazilin on GLUT4 recruitment in isolated rat epididymal adipocytes

The effects of brazilin on glucose transport into isolated rat epididymal a dipocytes were investigated. Brazilin increased [H-3]2-deoxy-D-glucose upta ke, which was characterized by an increase in V-max with no effect on the K -m value. Phenylarsine oxide, which inhibits the translocation of glucose t ransporters, decreased brazilin-stimulated glucose transport to the basal l evel. The inhibition of phosphatidylinositol 3-kinase (PI3-kinase) with wor tmannin also blocked brazilin-stimulated glucose transport. Western blot an alysis with an anti-GLUT4 antibody revealed that brazilin increased the tra nslocation of GLUT4 from intracellular pools to the plasma membrane. Brazil in, in combination with phorbol ester, showed an additive effect on glucose transport. The stimulating effect of phorbol ester on glucose transport wa s inhibited by staurosporine, but the effect of brazilin remained unchanged . Protein kinase C activity was not influenced by brazilin treatment. The i nhibition of protein synthesis showed no effect on brazilin stimulated gluc ose transport, and GLUT4 content in the total membrane fraction was not alt ered as a result of treatment with brazilin for 4 hr. Metabolic labeling of GLUT4 with [S-35]methionine showed that de novo synthesis of GLUT4 was not induced by brazilin. These data suggest that brazilin may increase glucose transport by recruitment of GLUT4 from intracellular pools to the plasma m embrane of adipocytes via the activation of PI3-kinase. However, the effect of brazilin may not be mediated by GLUT4 synthesis and protein kinase C ac tivation. BIOCHEM PHARMACOL 58;11:1705-1712, 1999. (C) 1999 Elsevier Scienc e Inc.