Na+-K+ and HCO-3 ATPase activity in retina: dependence on calcium and sodium.

With the use of homogenates of whole rat retina, the activities of Na+-K+-- and HCO-3-stimulated ATPases were measured in media containing different concentrations of calcium and sodium ions. In comparison to the Na+-K+ ATPase activity observed in the presence of 2 mM calcium and 130 mM sodium, the omission of calcium from the medium led to a 16-fold increase in activity. Furthermore, the omission of calcium and the reduction of the concentration of sodium in the medium to 25 mM also resulted in an increase in activity of ninefold. This study also demonstrates, for the first time, the existence of a HCO-3 stimulated. ATPase activity in the retina. These results are discussed in relation to recent observations on the effects of calcium- and bicarbonate-free media on the electrical and metabolic activities of the rat retina.