EFFECT OF INSULIN ON FATTY-ACID UPTAKE AND ESTERIFICATION IN L-CELL FIBROBLASTS

2We examined the effects of insulin on fatty acid uptake in L-cell fib roblasts, using cis-parinaric acid to measure uptake rates in the abse nce of esterification and [H-3]oleic acid to measure uptake rates in t he presence of esterification. L-cells exhibited both high and low aff inity insulin binding sites with K-d of 23 nM and 220 nM and a cellula r density of 1.4 and 6.8 x 10(5) sites/cell, respectively. Insulin in the range 10(-9) to 10(-7) M significantly decreased both the initial rate and maximal extent of cis-parinaric acid uptake by 24 to 30%. Ins ulin also reduced [H-3]oleic acid uptake up to 35%, depending on insul in concentration and decreased the amount of fatty acid esterified int o the phospholipids and neutral lipids by 28 and 70%, respectively. In contrast, glucagon or epinephrine stimulated both the initial rate an d extent of cis-parinaric acid uptake 18 and 25%, respectively, Becaus e L cells lack beta-adrenergic receptors, the epinephrine effect was n ot the result of beta-receptor stimulation. Hence, insulin altered not only fatty acid uptake, as determined by cis-parinaric and oleic acid uptake, but also altered the intracellular oleic acid esterification. (C) 1996 Academic Press,Inc.