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 µM albumin, hepatocyte clearance rates of unbound [3H]palmitate from hypophysectomized animals (0.16 ± 0.01 and 0.64 ± 0.01 mL·s-1·10-6cells, respectively) were significantly lower (p < 0.01) than those of the sham group (0.30 ± 0.02 and 1.00 ± 0.06 mL·s-1·10-6cells, respectively). However, the unbound [3H]palmitate clearance rates from the clofibrate-treated group (0.39 ± 0.04 and 1.18 ± 0.12 mL·s-1·10-6cells) were significantly higher (p < 0.01) than the control group (0.29 ± 0.02 and 0.81 ± 0.05 mL·s-1·10-6cells) for 2 and 20 µM 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 = CL20µM/CL2µM. 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.Key words: palmitic acid, albumin, growth hormone, liver, fatty acid binding protein, uptake, hepatic, long-chain fatty acids, clofibrate, hypophysectomy.