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Several studies suggest that a portion of hepatocellular nonesterified fatty acid uptake may be carrier mediated. To further investigate this process, initial rates (Vo) of 14Coleate uptake into rat hepatocytes, isolated by collagenase perfusion and incubated at 37 degrees C with oleate in the presence of bovine serum albumin, were studied as a function of the concentration of unbound 14Coleate in the medium. Vo was saturable with increasing unbound oleate concentration (Km = 8.3 X 10(-8) M; Vmax = 197 pmol per min per 5 X 10(4) hepatocytes) and was not inhibited by up to 40 microM sulfobromophthalein, taurocholate, or cholic acid. Oleate uptake was sodium dependent. Vo 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 14Coleate uptake was examined. Preincubation of hepatocytes with the IgG fraction of this antiserum inhibited Vo of 14Coleate by up to 65% in dose-related fashion, without altering Vo for 35Ssulfobromophthalein, 14Ctaurocholate, or 3Hcholate. 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.
Stremmel et al. (Sun,) studied this question.