Characterization of [formula omitted] exchange in cultured bovine pigmented ciliary epithelium

Abstract

Many recent data indicate that transport of Cl − across the ciliary epithelium plays an important role in aqueous humor formation. We used 36Cl to investigate the pathways for Cl −-transport in confluent monolayers of cultured bovine pigmented ciliary epithelial cells. Cl −-uptake mainly occurred via a mechanism with typical characteristics of an anion exchanger, and could be stimulated by an outwardly directed HCO 3 − gradient. One m m SITS and 1 m m DIDS inhibited Cl −, I − and Br −, by NO 3 −, formate and acetate. Inhibition of Cl − uptake by extracellular HCO 3 − was less effective in the absence of extracellular Na +, suggesting that not only HCO 3 − but also an action of loop-diuretics on the anion exchanger. 36Cl − uptake was cis-inhibited by the halides Cl −, I − and Br −, by NO 3 −, formate and acetate. Inhibition of Cl − uptake by extracellular HCO 3 − was less effective in the absence of extracellular Na +, suggesting that not only HCO 3 − but also NaCO 3 − binds to the carrier. SO 4 2−, cyclamate and gluconate did not significantly reduce Cl − uptake via the anion exchanger. DIDS-sensitive Cl − uptake showed saturation kinetics with respect to the Cl − concentration with an apparent K m of 8 m m. Cl − efflux could be stimulated by external Cl − and HCO 3 − and was inhibited by DIDS. Thus, cultured bovine pigmented ciliary epithelial cells express a Cl − HCO 3 − exchanger. A possible role of this carrier system for aqueous humor formation is discussed.