It has been almost a century since it was shown that calcium is elevated in cataractous lenses
1 and 75 years since total lens calcium was measured in clear lenses.
2 More recent work has confirmed a more than 23-fold increase in total lens calcium with cataract
(Tables 1 2) .
1 2 3 4 5 6 7 8 9 Maintenance of calcium homeostasis is critical to the clarity of the lens.
12 13 14 The inward passive diffusion of calcium, perhaps through a nonspecific cation channel,
15 is countered by the actions of the plasma and sarco- and endoplasmic reticular Ca
2+-adenosine triphosphatase (ATPase) pumps.
16 17 18 19 20 21 With age, the increased entry of calcium into clear lenses is offset by an increase in the activity of Ca
2+-ATPase pumps.
22 With cataract, however, lens membrane permeability increases further,
23 24 25 26 total lens calcium is elevated,
1 2 3 4 5 6 7 8 9 and Ca
2+-ATPase activity is decreased by 50%.
27 The Ca
2+-ATPase pump is sensitive to lipid order,
28 29 which changes with age
29 and cataract.
27 31 32 Accordingly, the decrease of Ca
2+-ATPase activity with cataract
27 may be a consequence of lipid structural changes,
27 31 32 an increase in Ca
2+-ATPase oxidation, or both.
33 34 35