Identification of lactate as a driving force for prostanoid transport by prostaglandin transporter PGT

We previously characterized the prostaglandin (PG) transporter PGT as an exchanger in which [³H]PGE₂ influx is coupled to the efflux of a countersubstrate. Here, we cultured HeLa cells that stably expressed human PGT under conditions known to favor glycolysis (glucose as a carbon source) or oxidative phosphorylation (glutamine as a carbon source) and studied the effect on PGT-mediated [³H]PGE₂ influx. PGT-expressing cells grown in glutamine exhibited a 2- to 4-fold increase in [³H]PGE₂ influx compared with the antisense control, whereas cells grown in glucose exhibited a 14-fold increase. In the presence of 10 vs. 25 mM glucose during the uptake, there was a dose-dependent increment in [³H]PGE₂ influx. Cis inhibition of [³H]PGE₂ influx occurred with lactate at physiological concentrations (apparent K_m = 48 ± 12 mM). Preloading with lactate caused a dose-dependent trans stimulation of PGT-mediated [³H]PGE₂ uptake, and external lactate caused trans stimulation of PGT-mediated [³H]PGE₂ release. Together, these data are consistent with PGT-mediated PG-lactate exchange. Cells engaged in glycolysis would then be poised energetically for prostanoid uptake by means of PGT.