Hepatocellular uptake of oleate is energy dependent, sodium linked, and inhibited by an antibody to a hepatocyte plasma membrane fatty acid binding protein

Abstract

Several studies suggest that a portion of hepatocellular nonesterfied fatty acid uptake may be carrier mediated. To further investigate this process, initial rate (V(o)) of [14C]oleate uptake into rat hepatocytes, isolated by collagenase perfusion and incubated at 37°C with oleate in the presence of bovine serum albumin, were studied as a function of the concentration of unbound [14C]oleate in the medium. V(o) was saturable with increasing unbound oleate concentration (K(m) = 8.3 x 10-8 M; V(max) = 197 pmol per min per 5 x 104 hepatocytes) and was not inhibited by up to 40 μM sulfobromophthalein, taurocholate, or cholic acid. Oleate uptake was sodium dependent. V(o) was significantly diminished when Li+, K+, choline, or sucrose were substituted for Na+ in the incubation medium and was reduced 46% by 1 mM ouabain. Uptake was also markedly reduced after exposure of cells to metabolic inhibitors (e.g., 2,4-dinitrophenol, carbonyl cyanide m-chlorophenylhydrazone, antimycin, KCN). To evaluate the physiologic significance of the previously isolated rat liver plasma membrane fatty acid-binding protein, the effect of an antibody directed against this protein on hepatocellular [14C]oleate uptake was examined. Preincubation of hepatocytes with the IgG fraction of this antiserum inhibited V(o) of [14C]oleate by up to 65% in dose-related fashion, without altering V(o) for [35S]sulfobromophthalein, [14C]taurocholate, or [3H]cholate. These data indicate that at least a portion of hepatocellular oleate uptake is energy dependent, sodium linked, and mediated by a specific liver plasma membrane-fatty acid-binding protein.