pHi-dependent Cl-HCO3 exchange at the basolateral membrane of frog retinal pigment epithelium

Intracellular pH (pHi) measurements in frog retinal pigment epithelium using the pH-sensitive dye 2',7'-bis(carboxyethyl)-5(6)-carboxyfluorescein demonstrate that the basolateral membrane contains a pHi-sensitive Cl-HCO3 exchanger. In control Ringer solution, the removal of Cl from the basal bath alkalinized the cells by 0.07 +/- 0.03 (SD) pH units (n = 39) with an initial rate of 0.022 +/- 0.0013 pH units/min. This effect was blocked by 0.5 mM basal 4,4'-diisothiocyanostilbene-2,2'- disulfonic acid or the removal of HCO3 from both the apical and basal baths. The rate of the exchange is reduced by acidification and increased by alkalinization. Increasing apical bath K concentration ([K]o) from 2 to 5 mM approximates the [K]o change in the subretinal space of the intact eye following a transition from light to dark. This [K]o change alkalinized the cells by increasing the rate of the apical membrane Na-HCO3 cotransporter. In 5 mM apical [K]o, the initial rate of the 0 Cl-induced alkalinization was significantly increased to 304 +/- 13% (n = 4) of control (2 mM [K]o). These mechanisms regulate pHi and could also buffer changes in subretinal pH.