Involvement of calpain in diamide-induced cataract in cultured lenses.

Lenses cultured in diamide first developed outer cortical opacities followed by nuclear cataract. Lens hydration and total calcium were markedly increased by diamide. Proteolysis of crystallins were observed in nuclear cataract lenses. Calpain in the soluble fraction of lenses cultured with diamide was decreased, while calpain in the insoluble fraction was increased. Co-culture with E64d, an inhibitor of cysteine protease such as calpain, especially prevented nuclear opacities and proteolysis of crystallins, indicating that calpain was involved in cataract formation by diamide.