Effect of thiol reagents on Ca-ATPase in rabbit lens epithelium

The inhibitory effects of sulfhydryl reagents on Ca-ATPase activity in the rabbit lens epithelium were assessed. Test compounds used in this study were selected on their ability to cause a calcium increase in cultured lenses. Under conditions in which lenses were cultured in the presence of the test compound, epithelial Ca-ATPase was inhibited markedly by diamide, t-BHP, IAA and slightly by selenite. The findings demonstrated that hydrogen peroxide caused little inhibition of Ca-ATPase in the lens epithelium, both when the intact lens was cultured in the presence of the oxidant or when the epithelial homogenate contained peroxide during the assay of enzyme activity. The study suggests that if a thiol-modifying compound can reach Ca-ATPase or its critical SH groups, inhibition is likely.