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Supriya S. Jalimarada, Diego G. Ogando, Eranga N. Vithana, Joseph A. Bonanno; Ion Transport Function of SLC4A11 in Corneal Endothelium. Invest. Ophthalmol. Vis. Sci. 2013;54(6):4330-4340. doi: 10.1167/iovs.13-11929.
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© ARVO (1962-2015); The Authors (2016-present)
Mutations in SLC4A11, a member of the SLC4 superfamily of bicarbonate transporters, give rise to corneal endothelial cell dystrophies. SLC4A11 is a putative Na+ borate and Na+:OH− transporter. Therefore we ask whether SLC4A11 in corneal endothelium transports borate (B[OH] 4 −), bicarbonate (HCO3 −), or hydroxyl (OH−) anions coupled to Na+.
SLC4A11 expression in cultured primary bovine corneal endothelial cells (BCECs) was determined by semiquantitative PCR, SDS-PAGE/Western blotting, and immunofluorescence staining. Ion transport function was examined by measuring intracellular pH (pHi) or Na+ ([Na+]i) in response to Ringer solutions with/without B(OH)4 − or HCO3 − after overexpressing or small interfering RNA (siRNA) silencing of SLC4A11.
SLC4A11 is localized to the basolateral membrane in BCEC. B(OH)4 − (2.5–10 mM) in bicarbonate-free Ringer induced a rapid small acidification (0.01 pH unit) followed by alkalinization (0.05–0.1 pH unit), consistent with diffusion of boric acid into the cell followed by B(OH)4 −. However, the rate of B(OH)4 −-induced pHi change was unaffected by overexpression of SLC4A11. B(OH)4 − did not induce significant changes in resting [Na+ i] or the amplitude and rate of acidification caused by Na+ removal. siRNA-mediated knockdown of SLC4A11 (∼70%) did not alter pHi responses to CO2/HCO3 −-rich Ringer, Na+-free induced acidification, or the rate of Na+ influx in the presence of bicarbonate. However, in the absence of bicarbonate, siSLC4A11 knockdown significantly decreased the rate (43%) and amplitude (48%) of acidification due to Na+ removal and recovery (53%) upon add-back. Additionally, the rate of acid recovery following NH4 + prepulse was decreased significantly (27%) by SLC4A11 silencing.
In corneal endothelium, SLC4A11 displays robust Na+-coupled OH− transport, but does not transport B(OH)4 − or HCO3 −.
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