The development of cataracts is a phenomenon in which 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. [1][2][3][4][5][6] Cataractous lenses have an altered distribution of the intracellular ionic environment. In human senile cataract, Dilsiz et al. 6) reported that lens ionic imbalance with increased levels of calcium (Ca 2ϩ ) and sodium (Na ϩ ), coupled with decreased levels of magnesium (Mg 2ϩ ) and potassium (K ϩ ), 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 2ϩ concentration in the lens becomes elevated. The elevated Ca 2ϩ concentration in the lens has been induced to activate calpain, a Ca 2ϩ -dependent protease. Furthermore, the degradation of lens proteins such as crystallin proteins would result in an opaque lens. 6,7) A decrease of plasma membrane Ca 2ϩ -ATPase, which regulates the Ca 2ϩ concentration in the lens, is one possible reason for the increase of Ca 2ϩ concentration in cataract development. However, this possibility is very unlikely, because our previous report showed that Ca 2ϩ -ATPase gene expression and activity in UPL rats, which is a hereditary cataract model rat, lenses increased with the progression of lens opacification. 8) 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. 8) Therefore, it is possible that the increase of Ca 2ϩ concentration in cataract development is caused by decrease of plasma membrane Ca 2ϩ -ATPase function.The present study assesses the effects of Mg 2ϩ deficiency on NO production, the ATP level and ATPase activity in human lens epithelial (HLE) cells. Ibaraki et al. 9) established the human lens epithelial cell line, SRA 01/04.
MATERIALS AND METHODS
Cell Culture and TreatmentsThe HLE cells were donated by Professor Ibaraki (Jichi Medical School Hospital, Ibaraki, Japan). The HLE cells were cultured in Dulbecco's Modified Eagle Medium containing either a normal (Mg 2ϩ 0.77 mM, Invitrogen, Tokyo, Japan) or Mg 2ϩ -deficient concentration (Mg 2ϩ 0.021 mM, Nissui Pharmaceutical Co. Ltd., Japan), supplemented with heat-inactivated fetal bovine serum 10 (v/v) % and gentamicin 10 mg/l. The Mg 2ϩ -deficient medium used according to the concentration of Mg 2ϩ markedly increased the production of IL-1b, TNF-a by rat alveolar macrophages. 10) All cultures were performed in a chamber with a 5% CO 2 atmosphere and 100% humidity at 37°C. In order to compare normal Mg 2ϩ and Mg 2ϩ -deficient medium, two experiments were performed. Each treatment ...
