Carrier-mediated lactate entry into isolated hepatocytes from fed and starved rats: zonal distribution and temperature dependence.

We examined the possibility of quantitative differences in lactate entry into periportal and perivenous hepatocytes under different nutritional states. The rate of 14C-L(+)-lactate uptake was determined after 15-second incubations with freshly isolated zonally separated hepatocytes using a centrifuge stop technique at 37 degrees C and 4 degrees C, in the presence or absence of either differing amounts of unlabelled lactate or of a hepatocyte lactate transport inhibitor, alpha-cyano-3-hydroxycinnamate. Total entry as well as carrier mediated entry of 14C-L(+)-lactate into the isolated cell populations was found to be similar in periportal and perivenous hepatocytes, irrespective of the nutritional state of the animal. Periportal and perivenous hepatocytes showed a greater tendency to transport lactate when isolated from starved animals, in agreement with previously reported data from non-zonally separated isolated hepatocytes. The activity of the hepatocyte plasma-membrane lactate transporter was diminished between fourfold and eightfold in transport studies conducted at 4 degrees C; similar results were obtained in unseparated and zonally separated suspensions. Temperature dependence of the hepatocyte transporter is markedly less than that reported for the erythrocyte transporter.