Effects of Oleate and Insulin on Glucose Uptake, Oxidation, and Glucose Transporter Proteins in Rat Adipocytes ERIK MURER, GUENTHER BODEN, MICHAEL GYDA, AND FRANCESCO DELUCA
We examined effects of Na oleate on glucose uptake, glucose transporter protein concentrations, and glucose oxidation in isolated adipocytes from fed rats. Na oleate increased basal 14C-glucose uptake in a dose-dependent manner (+42% with 1.0 mM, +79% with 2.8 mM Na oleate), but had no statistically significant effect on insulin-stimulated glucose uptake. Insulin (100 nM) resulted in a redistribution of GLUT4 protein concentration from the LDM fraction (-42%) to the PM fraction (+266%) but did not affect the distribution of GLUT1. Na oleate had no effect on basal or insulin-stimulated concentrations of GLUT1 or GLUT4 proteins in the PM or LOM fractions. Na oleate (2.8 mM) had no statistically significant effect on basal glucose oxidation, but inhibited insulin-stimulated glucose oxidation by 48% (P < 0.01). In summary, Na oleate inhibited insulin-stimulated glucose oxidation and stimulated basal glucose uptake in isolated adipocytes without affecting PM or LDM distribution of GLUT1 or GLUT4 proteins. We conclude that the stimulatory effect of Na oleate on basal glucose uptake in adipocytes may be mediated by changes in the intrinsic activity of the glucose transporters. Diabetes 41:1063-68, 1992
From the Division of Endocrinology and Metabolism; the General Clinical Research Center, Temple University Hospital; and the Department of Medicine, the Graduate Hospital, Philadelphia, Pennsylvania. Address correspondence and reprint requests to Guenther Boden, MD, Temple University Hospital, Broad & Ontario Streets, Philadelphia, PA 19140. Received for publication 8 October 1991 and accepted in revised form 30 March 1992. LDM, low-density microsomal membrane; PM, plasma membrane; FAT OX, fat oxidation; CHO OX, carbohydrate oxidation; BSA, bovine serum albumin; 2-DOG, 2-Deoxyglucose; TES, tris-EDTA-0.255 M sucrose; HDM, highdensity microsomal membrane; cpm, counts per minute; NS, no significance; FFA, free fatty acid.
DIABETES, VOL. 41, SEPTEMBER 1992
M
ore than 25 yr ago, Randle et al. (1) demonstrated that increased availability of fatty acids enhanced FAT OX and decreased CHO OX and glucose uptake in perfused rat heart and to a lesser extent in rat diaphragm. Based on these findings, they proposed a glucose-fatty acid cycle presumed to be of fundamental importance for the control of blood glucose and insulin sensitivity (1). Since then, many in vivo studies have confirmed the inhibitory action of increased FAT OX on CHO OX, at least under hyperinsulinemic conditions (2-11). On the other hand, much controversy remains as to whether increased FAT OX also inhibits glucose uptake. In vivo, inhibition of glucose uptake by fatty acids appears to be time dependent. It was observed only in studies lasting >3 h (4,8,9,11), but not in studies lasting
We examined effects of Na oleate on glucose uptake, glucose transporter protein concentrations, and glucose oxidation in isolated adipocytes from fed rats. Na oleate increased basal 14C-glucose uptake in a dose-dependent manner (+42% with 1.0 mM, +79% with 2.8 mM Na oleate), but had no statistically significant effect on insulin-stimulated glucose uptake. Insulin (100 nM) resulted in a redistribution of GLUT4 protein concentration from the LDM fraction (-42%) to the PM fraction (+266%) but did not affect the distribution of GLUT1. Na oleate had no effect on basal or insulin-stimulated concentrations of GLUT1 or GLUT4 proteins in the PM or LOM fractions. Na oleate (2.8 mM) had no statistically significant effect on basal glucose oxidation, but inhibited insulin-stimulated glucose oxidation by 48% (P < 0.01). In summary, Na oleate inhibited insulin-stimulated glucose oxidation and stimulated basal glucose uptake in isolated adipocytes without affecting PM or LDM distribution of GLUT1 or GLUT4 proteins. We conclude that the stimulatory effect of Na oleate on basal glucose uptake in adipocytes may be mediated by changes in the intrinsic activity of the glucose transporters. Diabetes 41:1063-68, 1992
From the Division of Endocrinology and Metabolism; the General Clinical Research Center, Temple University Hospital; and the Department of Medicine, the Graduate Hospital, Philadelphia, Pennsylvania. Address correspondence and reprint requests to Guenther Boden, MD, Temple University Hospital, Broad & Ontario Streets, Philadelphia, PA 19140. Received for publication 8 October 1991 and accepted in revised form 30 March 1992. LDM, low-density microsomal membrane; PM, plasma membrane; FAT OX, fat oxidation; CHO OX, carbohydrate oxidation; BSA, bovine serum albumin; 2-DOG, 2-Deoxyglucose; TES, tris-EDTA-0.255 M sucrose; HDM, highdensity microsomal membrane; cpm, counts per minute; NS, no significance; FFA, free fatty acid.
DIABETES, VOL. 41, SEPTEMBER 1992
M
ore than 25 yr ago, Randle et al. (1) demonstrated that increased availability of fatty acids enhanced FAT OX and decreased CHO OX and glucose uptake in perfused rat heart and to a lesser extent in rat diaphragm. Based on these findings, they proposed a glucose-fatty acid cycle presumed to be of fundamental importance for the control of blood glucose and insulin sensitivity (1). Since then, many in vivo studies have confirmed the inhibitory action of increased FAT OX on CHO OX, at least under hyperinsulinemic conditions (2-11). On the other hand, much controversy remains as to whether increased FAT OX also inhibits glucose uptake. In vivo, inhibition of glucose uptake by fatty acids appears to be time dependent. It was observed only in studies lasting >3 h (4,8,9,11), but not in studies lasting
