Chloride- and Bicarbonate-Stimulated ATPase Activity in Bovine Lens Epithelium

Abstract

An anion-stimulated, ouabain-insensitive Mg²⁺ATPase activity has been found in fresh homogenates prepared from capsules and epithelia of bovine lenses. Approximately equal activity was observed in the presence of HCO₃^–– or of Cl^––. The stimulation of each anion obeys saturation kinetics, with an optimum at approximately 20 m M Cl^–– or HCO₃^––. Whereas SCN^–– inhibits anion-activated ATPase in most other tissues, it failed to inhibit Cl^–– or HCO₃^––stimulated ATPase activity in the bovine lens. On the contrary, SCN^–– proved a potent activator of the enzyme. However, in keeping with other tissues, OCN^–– and the diuretic drugs, furosemide and ethacrynic acid are inhibitory. ATP is the primary substrate for the enzyme, which also shows some activity on GTP, ITP, and even ADP. Little Na⁺/ K⁺-dependent ATPase activity was observed in the fresh homogenate, but it increased in lyophilized preparations. In contrast, the lyophilized preparations showed no anion-dependent ATPase activity. It is postulated that active bicarbonate ion transport in the lens may be mediated by this anion-dependent ATPase.