CALCIUM-ACTIVATED PROTEOLYSIS IN THE LENS NUCLEUS DURING SELENITE CATARACTOGENESIS

  • 1 January 1984
    • journal article
    • research article
    • Vol. 25  (11) , 1275-1283
Abstract
A single injection of 20 .mu.mol sodium selenite/kg body wt in 10-day old rats caused severe nuclear cataract within 4 days. By 4 days postselenite injection, nuclear Ca levels increased from 0.4 to 6.8 mmol/kg lens dry wt. An attempt was made to determine if this Ca increase was associated with proteolysis specifically in the lens nuclear region. Sodium dodecyl sulfate polyacrylamide electrophoresis of lens nuclear proteins following selenite injection showed: loss of 30, 27 and 26 K [kilodalton] MW polypeptides in the soluble fraction, loss of 83, 52, 30, 27 and 26 K polypeptides in the insoluble fraction and loss of the major 26 K membrane protein. Gel chromatography of nuclear soluble proteins indicated a decrease in .beta.H and .beta.L crystallins following selenite injection. In vitro incubation (2 h) of nuclear lens homogenates with Ca duplicated many of the proteolytic changes occurring in lenses in vivo following selenite injection. Ca induced proteolysis in vitro was inhibited by EGTA [ethylene glycol bis (.beta.-aminoethyl ether)N-tetraacetic acid], leupeptin and iodoacetate but was not inhibited by phenylmethylsulfonyl fluoride. These properties are similar to Ca activated protease (CAP) from other tissues. CAP activation and subsequent nuclear protein degradation may be causes of selenite cataract.