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Tracy T. Nguyen, Joseph A. Bonanno; Bicarbonate, NBCe1, NHE, and Carbonic Anhydrase Activity Enhance Lactate-H+ Transport in Bovine Corneal Endothelium. Invest. Ophthalmol. Vis. Sci. 2011;52(11):8086-8093. doi: 10.1167/iovs.11-8086.
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© 2016 Association for Research in Vision and Ophthalmology.
To identify and localize the monocarboxylate transporters (MCTs) expressed in bovine corneal endothelial cells (BCEC) and to test the hypothesis that buffering contributed by HCO3 −, sodium bicarbonate cotransporter (NBCe1), sodium hydrogen exchanger (NHE), and carbonic anhydrase (CA) activity facilitates lactate flux.
MCT1–4 expression was screened by RT-PCR, Western blot analysis, and immunofluorescence. Endogenous lactate efflux and/or pHi were measured in BCEC in HCO3 −-free or HCO3 −-rich Ringer, with and without niflumic acid (MCT inhibitor), acetazolamide (ACTZ, a CA inhibitor), 5-(N-Ethyl-N-isopropyl)amiloride (EIPA) (Na+/H+ exchange blocker), disodium 4,4′-diisothiocyanatostilbene-2,2′-disulfonate (DIDS; anion transport inhibitor), or with NBCe1-specific small interfering (si) RNA-treated cells.
MCT1, 2, and 4 are expressed in BCEC. MCT1 was localized to the lateral membrane, MCT2 was lateral and apical, while MCT4 was apical. pHi measurements showed significant lactate-induced cell acidification (LIA) in response to 20-second pulses of lactate. Incubation with niflumic acid significantly reduced the rate of pHi change (dpHi/dt) and lactate-induced cell acidification. EIPA inhibited alkalinization after lactate removal. Lactate-dependent proton flux was significantly greater in the presence of HCO3 − but was reduced by ACTZ. Efflux of endogenously produced lactate was significantly faster in the presence of HCO3 −, was greater on the apical surface, was reduced on the apical side by ACTZ, as well as on the apical and basolateral side by NBCe1-specific siRNA, DIDS, or EIPA.
MCT1, 2, and 4 are expressed in BCEC on both the apical and basolateral membrane (BL) surfaces consistent with niflumic acid-sensitive lactate-H+ transport. Lactate dependent proton flux can activate Na+/H+ exchange and be facilitated by maximizing intracellular buffering capacity through the presence of HCO3 −, HCO3 − transport, NHE and CA activity.
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