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S. Majumdar, S. Gunda, D. Pal, A.K. Mitra; Identification and Characterization of a Monocarboxylic Acid Transport System on the Human Retinal Pigment Epithelium Cell Line – ARPE-19 . Invest. Ophthalmol. Vis. Sci. 2003;44(13):3464.
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Purpose: The purpose of this study is to identify and characterize the expression of monocarboxylic acid transport systems on the human retinal pigment epithelial (RPE) cell line ARPE-19. Methods: Uptake studies were carried out at 37oC using ARPE-19 cells. [14C]L-lactic acid was used as the model substrate for the transporter. Results: Uptake of [14C]lactic acid by ARPE-19 was found to exhibit saturable kinetics (Km = 2.7 ± 0.4 mM, Vmax =58.7 ± 4.5 pmole/min/mg of protein). Monocarboxylic acids, such as salicylic acid and pyruvic acid, inhibited the uptake of [14C]lactic acid whereas di- and tri- carboxylic acids, such as phthallic acid, succinic acid and citric acid, did not demonstrate any inhibitory effect. Uptake was stereospecific - D-lactic acid was less effective in inhibiting [14C]lactic acid uptake than L-lactic acid. Increase in uptake was observed as the pH of uptake medium was decreased from 7.4 to 5.0. Moreover, inhibition of [14C]lactic acid uptake was observed in the presence of the protonophores, FCCP and 2,4 dinitrophenol. The data thus suggests that uptake of [14C]lactic acid involves a proton coupled transport system. Further, uptake was decreased in the presence of sodium azide. Known organic anion transporter substrates, p-amino hippuric acid and probenecid, and inhibitors, DIDS, did not inhibit [14C]lactic acid transport suggesting that organic anion transporters are not involved. Conclusions: Our results indicate that ARPE-19 expresses a stereospecific, energy dependent, proton coupled monocarboxylic acid transport system on its apical side.
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