Calcium content and distribution in human cataract

Abstract

The calcium content and distribution was measured in brunescent cataracts from India and cataracts from the United States classified according to guidelines of the Cooperative Cataract Research Group (CCRG). The severity and extent of opacification correlates well with the increase in Ca 2+ bound to membranes and insoluble proteins separated by differential centrifugation. Thus, bound Ca 2+ is approximately 30 ng/mg for the immature cataract. 100 ng/mg for the pale yellow. 200 ng/mg for the mature cataract and 300 ng/mg for the brown brunescent. These values can be compared to 16 ng/mg (0·2 m m) for a freshly excised rabbit lens. To the extent that the mature cataract represents an advanced stage and the immature cataract an early stage of development, and likewise for the brown and pale yellow cataract, results of this study suggest that cataract development is not accompanied by, or the result of, a redistribution of ‘free’ and bound calcium. We find that the fraction of total calcium bound to membranes and insoluble proteins is the same in the early and advanced stages of U.S. and Indian cataracts. It appears that as calcium accumulates in the developing cataract, an increasing amount becomes membrane or protein bound while the level of diffusible Ca 2+ continues to increase. In the advanced stage as much as 85% of the calcium in the 10 000 g supernatant is dialyzable or diffusible. The remaining 15% is bound to watersoluble proteins and represents a sixfold to 15-fold increase in the mature and brown cataract, respectively. There is also a considerable increase in the amount of calcium found in the 1000 g pellet containing insoluble proteins and membrane fragments.