Hepatocellular influx of [14C]oleate reflects membrane transport rather than intracellular metabolism or binding.

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Abstract
When [14C]oleate bound to bovine serum albumin was incubated at 37.degree. C for 7 min with isolated rat hepatocytes in the absence of glucose, the cumulative oleate uptake curve had two components: a rapid, linear segment over the first 30 sec, followed by a slower, curvilinear component. At 173 .mu.M [14C]oleate/albumin (1:1, mol/mol), the initial component had a slope (Vo) of 118 .+-. 18 pmol per min per 5 .times. 104 hepatocytes (mean .+-. SD). During this initial 30 sec, virtually no oleate was oxidized, and < 11% was esterified. By 5 min, 79% was esterified; oxidation never exceeded 4%. Addition of 2 mM glucose significantly increased oleate esterification and thereby available oleate binding sites on cytosolic fatty acid binding protein but had no influence on Vo. Pretreatment with trpysin reduced Vo by 49 .+-. 15%. These data indicate that the initial component of the oleate uptake curve reflects predominantly influx, whereas the subsequent component reflects a balance between influx, efflux, and intracellular metabolism. Influx is independent of intracellular binding, oxidation, and esterification and may reflect a membrane-associated carrier-mediated process.

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