E. Kenyon et al., APICAL AND BASOLATERAL MEMBRANE MECHANISMS THAT REGULATE PH(I) IN BOVINE RETINAL-PIGMENT EPITHELIUM, American journal of physiology. Cell physiology, 42(2), 1997, pp. 456-472
pH regulation was studied in fresh explant bovine retinal pigment epit
helium-choroid using the pH-sensitive dye 2',7'-bis(carboxyethyl)-5(6)
-carboxyfluores cein and intracellular microelectrodes. Acid recovery
was HCO3 dependent, inhibited by apical amiloride and apical or basal
4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS), and required
apical and basal Na. Alkali recovery was HCO3 dependent and inhibitabl
e by apical or basal DIDS. Three apical and two basolateral transporte
rs were identified. Four contribute to acid extrusion, i.e., apical Na
/h exchange, apical H-lactate cotransport, and apical Na-HCO3 cotransp
ort and basolateral Na-HCO3 cotransport. At least two contribute to al
kali extrusion, i.e., apical Na-HCO3 cotransport and a basolateral HCO
3-dependent, DIDS-inhibitable mechanism, possibly Na-HCO3 cotransport,
Cl/HCO3 exchange, or both. The apical Na-HCO3 cotransporter is electr
ogenic, carrying net negative charge inward. Basal Cl removal or addit
ion of basal HCO3 caused HCO3- and Cl-dependent alkalinizations, respe
ctively. Apical DIDS increased both responses. These cytosolic pH (pH(
i)) regulatory mechanisms are so tightly coupled that changes in pH(i)
can only occur after two or more of them are inhibited. In addition,
these mechanisms help provide pathways for transport of Na and HCO3 ac
ross the retinal pigment epithelium between the blood and the distal r
etina.