ATPase activities in retinal pigment epithelium and choroid

Abstract

The Mg 2−-, the Na +-K +- and the HCO 3 −-dependent ATPase activities of retinal pigment epithelium-choroid tissue from grassfrog, bullfrog and rabbit have been measured. In the frogs, Mg 2+ ATPase activity was between 1 and 2 μmols P i liberated hr −1 mg −1 protein, while Na +-K + ATPase and HCO 3 − ATPase were about 20 and 25% of this activity, respectively. Corresponding values for the rabbit were 8·5 μmol P i hr −1 mg −1 protein, 8% and 9%. Na +-K + ATPase activity in each species was completely inhibited by 2 m m-calcium, while HCO 3 − ATPase was unaffected by calcium or by ouabain. The pigment epithelium-choroid preparations of bullfrog and rabbit were scraped to yield suspensions of isolated epithelial cells, relatively free of other tissue components, and a residual fraction which contained some epithelial cells, choroidal elements and red blood cells. Na −-K + ATPase activity was present in the epithelial cells of both species and absent from the choroid of the rabbit. HCO 3 − ATPase and Mg 2+ ATPase activities were roughly equally distributed in the bullfrog fractions, but in the rabbit were concentrated in the choroid. The results are discussed in relation to the postulated active ion transport processes of the pigment epithelium.