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The Acute and Chronic Stimulatory Effects of Endothelin-1 on Glucose Transport Are Mediated by Distinct Pathways in 3T3-L1 Adipocytes¹

Department of Medicine, Division of Endocrinology and Metabolism, University of California, San Diego, La Jolla, California 92093-0673

Address all correspondence and requests for reprints to: Jerrold M. Olefsky, M.D., Department of Medicine (0673), University of California, San Diego, 9500 Gilman Drive, La Jolla, California 92093-0673. E-mail: jolefsky{at}ucsd.edu

We have recently shown that pretreatment with endothelin-1 (ET-1) for 20 min stimulates GLUT4 translocation in a PI3-kinase-dependent manner in 3T3-L1 adipocytes (Imamura, T. et al., J Biol Chem 274:33691–33695). This study presents another pathway by which ET-1 potentiates glucose transport in 3T3-L1 adipocytes. ET-1 treatment (10 nM) leads to approximately 2.5-fold stimulation of 2-deoxyglucose (2-DOG) uptake within 20 min, reaching a maximal effect of 4-fold at 6 h, and recovering almost to basal levels after 24 h. Insulin treatment (3 ng/ml) results in an approximately 5-fold increase in 2-DOG uptake at 1 h, and recovering to basal levels after 24 h. The ETA receptor antagonist, BQ 610, inhibited ET-1 induced glucose uptake both at 20 min and 6 h, whereas the ETB receptor antagonist, BQ 788, was without effect. Interestingly, ET-1 stimulated 2-DOG uptake at 6 h, not at 20 min, was almost completely blocked by the protein-synthesis inhibitor, cycloheximide and the RNA-synthesis inhibitor, actinomycin D, suggesting that the short-term (20 min) and long-term (6 h) effects of ET-1 involve distinct mechanisms. GLUT4 translocation assay showed that 20 min, but not 6 h, exposure to ET-1 led to GLUT4 translocation to the plasma membrane. In contrast, 6 h, but not 20 min, exposure to ET-1 increased expression of the GLUT1 protein, without affecting expression of GLUT4 protein. ET-1 induced 2-DOG uptake and GLUT1 expression at 6 h were completely inhibited by the MEK inhibitor, PD 98059, and partially inhibited by the PI3-kinase inhibitor, LY 294002, and the Gi inhibitor, pertussis toxin. The PLC inhibitor, U 73122, was without effect. These findings suggest that ET-1 induced GLUT1 protein expression is primarily mediated via MAPK, and partially via PI3K in 3T3-L1 adipocytes.

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