Evidence for a lactate transporter in the plasma membrane of the rat hepatocyte.

1. The rate of uptake in 15 s of L- and D-lactate was studied in isolated hepatocyte preparations from starved rats. 2. Observations were also made of the effect of different concentrations of unlabelled L- and D-lactate on L-[14C]- and D-[14C]-lactate uptake. 3. Lactate uptake into hepatocytes appears to occur by two processes, one saturable and at least partially stereospecific, the other non-saturable, at least up to 28 mmol/l, and probably representing simple non-carrier assisted diffusion. 4. The 15 s uptake of lactate is inhibited by alpha-cyano-3-hydroxycinnamate and by rho-chloromercuriphenylsulphonate but not by the general anion transporter inhibitor 4-acetamido-4'-isothiocyanostilbene-2,2'-disulphonic acid, ouabain or the structural analogue DL-rho-hydroxyphenyl-lactate. 5. Transporter-mediated lactate entry into liver cells is enhanced by lowered extracellular pH. 6. It is suggested that the contribution of the diffusion component of lactate entry into the cell may be exaggerated by the artifactual nature of the isolated hepatocyte preparation, and that under some circumstances in vivo, lactate transport into hepatocytes could determine the rate of lactate removal from blood.