Cytosolic fatty acid binding protein enhances rat hepatocyte [3H]palmitate uptake

Abstract

Liver cytosolic fatty acid binding protein (FABP) represents the intracellular equivalent to extracellular serum albumin, participating in the intracellular transport of long-chain fatty acids. In this study we observed the effect of increasing and decreasing FABP levels on hepatocyte [3H]palmitate uptake in male Sprague-Dawley rats. We also were interested to determine whether uptake, from either the unbound or unbound and protein-bound fractions, was fundamentally different at the different FABP levels. FABP levels were modified by hypophysectomy and clofibrate treatment (50 mg/100 g body weight for 10 days). Results showed that the [3H]palmitate clearance rates paralleled the 54% decrease and 73% increase in FABP levels in hypophysectomy and clofibrate-treated animals, respectively. In the presence of 2 and 20 microM albumin, hepatocyte clearance rates of unbound [3H]palmitate from hypophysectomized animals (0.16+/-0.01 and 0.64+/-0.01 mL x s(-1) x 10(-6) cells, respectively) were significantly lower (p<0.01) than those of the sham group (0.30+/-0.02 and 1.00+/-0.06 mL x s(-1) x 10(-6) cells, respectively). However, the unbound [3H]palmitate clearance rates from the clofibrate-treated group (0.39+/-0.04 and 1.18+/-0.12 mL x s(-1) x 10(-6) cells) were significantly higher (p<0.01) than the control group (0.29+/-0.02 and 0.81+/-0.05 mL x s(-1) x 10(-6) cells) for 2 and 20 microM albumin, respectively. To investigate whether uptake was fundamentally different between the hypophysectomized and clofibrate-treated groups, we expressed the clearance rates as enhancement factors, i.e., EF = CL20 microM/CL2microM. No statistical difference was observed between EF of the hypophsectomized (3.8+/-0.4) and EF of the clofibrate-treated (3.1+/-0.3) groups, suggesting that the extracted ligand originated from similar fractions.