Polarized Lactate Transporter Activity and Expression in the Syncytiotrophoblast of the Term Human Placenta

• Published in: Placenta (Eastbourne) 2004-07, Vol.25 (6), p.496-504
• Main Authors: Settle, P., Mynett, K., Speake, P., Champion, E., Doughty, I.M., Sibley, C.P., D'Souza, S.W., Glazier, J.
• Format: Article
• Language: English
• Subjects: 4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid - pharmacology; Antigens, CD - analysis; Antigens, Neoplasm - analysis; Basigin; Biological and medical sciences; Blotting, Western; Carbon Radioisotopes; CD147; Cell Membrane - chemistry; Cell Polarity; Embryology: invertebrates and vertebrates. Teratology; Female; Fundamental and applied biological sciences. Psychology; Human placenta; Humans; Immunohistochemistry; Kinetics; Labor, Obstetric; Lactate; Lactic Acid - chemistry; Lactic Acid - metabolism; Monocarboxylate transporter; Monocarboxylic Acid Transporters - analysis; Monocarboxylic Acid Transporters - antagonists & inhibitors; Monocarboxylic Acid Transporters - metabolism; Muscle Proteins - analysis; Polarization; Pregnancy; Stereoisomerism; Symporters - analysis; Symporters - antagonists & inhibitors; Trophoblasts - chemistry; Trophoblasts - metabolism
• ISSN: 0143-4004; 1532-3102
• DOI: 10.1016/j.placenta.2003.11.009

We investigated the polarization of l-lactate transport in human syncytiotrophoblast by measuring uptake of [ 14C] l-lactate by both microvillous (maternal-facing; MVM) and basal (fetal-facing; BM) plasma membranes. [ 14C] l-lactate uptake by MVM and BM was stimulated in the presence of an inwardly directed H +gradient, with a significantly higher uptake in MVM than in BM at initial rate (15.4±2.3 vs 5.6±0.6 pmol/mg protein/20 sec). Stereospecific inhibition was observed in MVM, with a higher affinity for l-lactate compared with d-lactate. In BM, there was no difference in the inhibition by these two stereoisomers. Inhibition of lactate uptake in both MVM and BM by 4,4′-diisothiocyanatostilbene-2,2′-disulfonic acid (DIDS), an inhibitor of monocarboxylate transporter (MCT) activity, indicated MCT-mediated mechanisms across both membranes. Kinetic modelling supported a two-transporter model as the best fit for both MVM and BM, the K mof the major component being 6.21 m m and 25.01 m m in MVM and BM respectively. Western blotting and immunolocalization examining the distribution of MCT1 and MCT4, showed that MCT expression was polarized, MCT1 being predominantly localized to BM and MCT4 showing greater abundance on MVM. CD147, a chaperone protein for MCT1 and MCT4, was equally expressed by both membranes. These studies demonstrate that the opposing plasma membranes of human syncytiotrophoblast are polarized with respect to both MCT activity and expression.