pH homeostasis in the frog retina: The role of Na+:HCO−3 co‐transport in the retinal pigment epithelium

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Abstract
Transport of acid/base equivalents across the isolated frog retinal pigment epithelium (RPE) was studied by means of pH selective microelectrodes. Abrupt changes in retinal extracellular pH, from 7.40 to values between 6.66 and 7.66, were found to cause rapid changes in both intracellular pH and choroidal extracellular pH. The initial rates of these changes were reduced by more than 60%, when the cellular Na+:HCO−3 co‐transport system was inhibited by Na+ removal, or by administration of 1 mM SITS. It is concluded that RPE transcellular HCO−3 transport changed in response to changes in retinal extracellular pH. If present in vivo these changes in RPE HCO−3 transport would tend to stabilize retinal extracellular pH. It is suggested that cellular Na+:HCO3− co‐transport plays a significant role for the retinal pH homeostasis.