Bicarbonate promotes dye coupling in the epithelium and endothelium of the rabbit cornea

Purpose. Examine the mechanism of bicarbonate maintenance of cell-to-cell coupling in rabbit corneal epithelium and endothelium. Methods. Carboxyfluorescein was microinjected into rabbit corneal epithelial and endothelial cells. Adjacent cells were observed for fluorescence. Bathing solutions were buffered with bicarbonate, HEPES, phosphate, or acetate-citrate. The influence of intracellular pH and transmembrane voltage (V_m) were examined. Results. Bicarbonate was the only buffer to increase dye coupling. Substitution of bicarbonate structural analogs bisulfite and carbamate in a HEPES-buffered solution increased dye coupling in both cell types. Intracellular pH and V_m alterations in corneal epithelial cells bathed in HEPES vs. bicarbonate buffered media had no significant effects on dye coupling. Conclusions. Bicarbonate increases intercellular communication in the corneal epithelium and endothelium. This effect appears to result from an interaction of the bicarbonate molecule (or one of its structural analogs) with either gap junction proteins or an intermediary. We also demonstrate the presence of Cx43 in the rabbit corneal endothelium.