Sodium-bicarbonate cotransport in retinal astrocytes and Muller cells of the rat

Sodium-bicarbonate cotransport in retinal glial cells was studied in the everted eyecup preparation of the rat. Intracellular pH was monitored with the indicator dye BCPCF and fluorescence confocal microscopy. Raising the K⁺ concentration from 3 to 12 mM in HCO₃^- buffered perfusate evoked an intracellular alkalinization in both astrocytes and Muller cells. The alkalinization developed more rapidly and was larger in astrocytes. The K⁺-induced alkalinization was HCO₃^- dependent; it was reduced by 33% in astrocytes and 71% in Muller cells when HCO₃^- was removed from the perfusate. The alkalinization was effectively blocked by addition of 0.5 mM 4,4'-diisothiocyanato-stilbene-2,2'-disulfonic acid (DIDS). Removal of Na⁺ from the perfusate evoked a rapid acidification in both types of glial cells. The results indicate that astrocytes and Muller cells in situ in the rat retina possess an electrogenic Na⁺/HCO₃^- cotransporter.