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-deoxyglucose uptake, reaching maximal effect at approximately 8 hr. Insulin-stimulated 2-deoxyglucose uptake was not altered over the experimental period. While the short-term (2-h exposure) effect of arachidonic acid was negligibly influenced by cycloheximide, the enhancement of glucose transport by long-term (8-h) exposure to arachidonic acid was markedly decreased by the simultaneous presence of protein-synthesis inhibitors, implying that the short-term and long-term effects of arachidonic acid may involve distinct mechanisms. Immunoblot analysis revealed that 8-h but not 2-h exposure to arachidonic acid increased the content of the ubiquitous glucose transporter (GLUT1) in both total cellular 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 Vmax of basal 2-deoxyglucose uptake was more than doubled, while the apparent Km for 2-deoxyglucose remained unchanged. Protein kinase C (PKC) depletion by pretreating cells with 4 beta-phorbol 12 beta-myristate 13 alpha-acetate (PMA) for 24 h had little influence on the subsequent enhancing effect of arachidonic acid on 2-deoxyglucose uptake. In addition, PMA was able to stimulate 2-deoxyglucose uptake in arachidonic-acid-pretreated cells with similar increments as in non-treated cells. Thus, our data seem to suggest that arachidonic acid may enhance the intrinsic activity of GLUT1 by a PKC-independent mechanism.
Fong
J C
JC
Institute of Biochemistry, National Yang-Ming University, Taipei, Taiwan, Republic of China.
Chen
C C
CC
Liu
D
D
Chai
S P
SP
Tu
M S
MS
Chu
K Y
KY
D016475:3T3 Cells; D017667:Adipocytes / Q000187:drug effects / Q000378:metabolism*; D000818:Animals; D000841:Anisomycin / Q000494:pharmacology; D016718:Arachidonic Acid / Q000494:pharmacology*; D003513:Cycloheximide / Q000494:pharmacology; D003847:Deoxyglucose / Q000493:pharmacokinetics; D004305:Dose-Response Relationship, Drug; D051272:Glucose Transporter Type 1; D051275:Glucose Transporter Type 4; D007328:Insulin / Q000494:pharmacology; D008715:Methionine / Q000493:pharmacokinetics; D051379:Mice; D009004:Monosaccharide Transport Proteins / Q000378:metabolism*; D009124:Muscle Proteins; D011493:Protein Kinase C / Q000378:metabolism*; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology
D051272:Glucose Transporter Type 1; D051275:Glucose Transporter Type 4; D007328:Insulin; D009004:Monosaccharide Transport Proteins; D009124:Muscle Proteins; D011500:Protein Synthesis Inhibitors; C495678:Slc2a1 protein, mouse; C495693:Slc2a4 protein, mouse; D016718:Arachidonic Acid; D000841:Anisomycin; D003513:Cycloheximide; D003847:Deoxyglucose; D008715:Methionine; D011493:Protein Kinase C