ARACHIDONIC-ACID STIMULATES THE INTRINSIC ACTIVITY OF UBIQUITOUS GLUCOSE-TRANSPORTER (GLUT1) IN 3T3-L1 ADIPOCYTES BY A PROTEIN-KINASE C-INDEPENDENT MECHANISM

Exposure of adipocytes to arachidonic acid rapidly enhanced basal 2-de oxyglucose uptake, reaching maximal effect at approximately 8 hr. Insu lin-stimulated 2-deoxyglucose uptake was not altered over the experime ntal period. While the short-term (2-h exposure) effect of arachidonic acid was negligibly influenced by cycloheximide, the enhancement of g lucose transport by long-term (8-h) exposure to arachidonic acid was m arkedly decreased by the simultaneous presence of protein-synthesis in hibitors, implying that the short-term and long-term effects of arachi donic acid may involve distinct mechanisms. Immunoblot analysis reveal ed that 8-h but not 2-h exposure to arachidonic acid increased che con tent of the ubiquitous glucose transporter (GLUT1) in both total cellu lar and plasma membranes. The insulin-responsive glucose transporter ( GLUT4), on the other hand, was not affected. Following 2-h exposure to arachidonic acid, kinetic studies indicated that the apparent V-max o f basal 2-deoxyglucose uptake was more than doubled, while the apparen t Km for 2-deoxyglucose remained unchanged. Protein kinase C (PKC) dep letion by pretreating cells with 4 beta-phorbol 12 beta-myristate 13 a lpha-acetate (PMA) for 24 h had little influence on the subsequent enh ancing effect of arachidonic acid on 2-deoxyglucose uptake. In additio n, PMA was able to stimulate 2-deoxyglucose uptake in arachidonic-acid -pretreated cells with similar increments as in non-treated cells. Thu s, our data seem to suggest chat arachidonic acid may enhance the intr insic activity of GLUT1 by a PKC-independent mechanism.