Expression and proteolytic activity of calpain in lens epithelial cells of oxidative cataract

OBJECTIVE: To study the role of calpain in the mechanism of oxidative cataract through detecting the level of intracellular free Ca(2+), the expression and proteolytic activity of calpain in the lens epithelial cells (LECs) of H(2)O(2)-induced cataract. METHODS: Rat lenses were cultured in vitro and cataract was induced by H(2)O(2). The level of intracellular free Ca(2+) was measured by fluorescence determination with fura-2/AM. The expression of m-calpain protein in LECs was detected with immunohistochemical method. The proteolytic activity in LECs was measured using a fluorogenic synthetic substrate. RESULTS: There were significant differences of the level of intracellular free Ca(2+) (P=0.001, 0.000, 0.000), the expression of m-calpain (P=0.001, 0.000, 0.000) and the proteolytic activity of calpain (P=0.001, 0.000, 0.000) between H(2)O(2)-induced and control group at 6, 12 and 24 h, respectively. CONCLUSIONS: H(2)O(2) can increase intracellular free Ca(2+), then enhance the expression and proteolytic activity of calpain which may play a role in the mechanism of oxidative cataract of rat.