Biol. Pharm. Bull. 30(1) 6—10 (2007)

the eye becomes opaque resulting in severe visual impairment. Numerous factors have been implicated in the etiology of cataracts, including genetic factors, diabetes, smoking, nutrition, the cumulative effect of X-rays, ultraviolet irradiation, and alteration in both endocrine and enzymatic equilibrium. Cataractous lenses have an altered distribution of the intracellular ionic environment. In human senile cataract, Dilsiz et al. reported that lens ionic imbalance with increased levels of calcium (Ca ) and sodium (Na ), coupled with decreased levels of magnesium (Mg ) and potassium (K ), is related to cataract development. Currently, reactive oxygen species (ROS), induced by UV rays in sunlight, are considered important in perturbing lens homeostasis. Therefore, exposure to ROS results in a breakdown of lens homeostasis, and the Ca concentration in the lens becomes elevated. The elevated Ca concentration in the lens has been induced to activate calpain, a Ca -dependent protease. Furthermore, the degradation of lens proteins such as crystallin proteins would result in an opaque lens. A decrease of plasma membrane Ca -ATPase, which regulates the Ca concentration in the lens, is one possible reason for the increase of Ca concentration in cataract development. However, this possibility is very unlikely, because our previous report showed that Ca -ATPase gene expression and activity in UPL rats, which is a hereditary cataract model rat, lenses increased with the progression of lens opacification. On the other hand, we previously reported that inducible nitric oxide synthase (iNOS) in lenses of UPL rat increased with the development of cataracts, and the increase of iNOS markedly decreased the ATP content in UPL rat lenses. Therefore, it is possible that the increase of Ca concentration in cataract development is caused by decrease of plasma membrane Ca -ATPase function. The present study assesses the effects of Mg deficiency on NO production, the ATP level and ATPase activity in human lens epithelial (HLE) cells. Ibaraki et al. established the human lens epithelial cell line, SRA 01/04.