PH(I)-DEPENDENT CL-HCO3 EXCHANGE AT THE BASOLATERAL MEMBRANE OF FROG RETINAL-PIGMENT EPITHELIUM

Intracellular pH (pH(i)) measurements in frog retinal pigment epitheli um using the pH-sensitive dye 2',7'-bis(carboxyethyl)-5(6)-carboxyfluo rescein demonstrate that the basolateral membrane contains a pH(i)-sen sitive Cl-HCO3 exchanger. In control Ringer solution, the removal of C l from the basal bath alkalinized the cells by 0.07 +/- 0.03 (SD) pH u nits (n = 39) with an initial rate of 0.022 +/- 0.0013 pH units/min. T his 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 basa l baths. The rate of the exchange is reduced by acidification and incr eased by alkalinization. Increasing apical bath K concentration ([K](0 )) from 2 to 5 mM approximates the [K](0) change in the subretinal spa ce of the intact eye following a transition from light to dark. This [ K](0) change alkalinized the cells by increasing the rate of the apica l membrane Na-HCO3 cotransporter. In 5 mM apical [K](0), the initial r ate of the 0 Cl-induced alkalinization was significantly increased to 304 +/- 13% (n = 4) of control (2 mM [K](0)). These mechanisms regulat e pH(i) and could also buffer changes in subretinal pH.