CALPASTATIN IN ERYTHROCYTES OF YOUNG AND OLD INDIVIDUALS

To gain knowledge about the behaviour of calpastatin (the specific inh ibitor of the Ca2+-dependent thiol protease calpain) in the intact cel l, we analysed the inhibitor by specific antibodies and determined its activity in erythrocytes from individuals 20-34 years old (young) and 70-93 years old (old). Differences between old and young in the behav iour of erythrocyte calpastatin were observed. Erythrocytes of old ind ividuals had lower amounts of calpastatin and less calpastatin activit y than those of young ones. A difference between old and young was als o found in the molecular-mass distribution of calpastatin subunits. In creasing the erythrocyte Ca2+ induced changes in calpastatin in young individuals, rendering it similar to calpastatin in cells of old indiv iduals. When calpastatin (isolated from erythrocytes of a young indivi dual) was added to erythrocyte membranes, the initial binding and subs equent association of calpastatin with the membrane were lower in old than in young individuals. We had previously found that calpain bindin g and activation were enhanced in erythrocyte membranes from old indiv iduals, along with enhanced degradation of band 3 (a major erythrocyte transmembrane anion-transport protein). The overall results indicate an interaction of calpain with calpastatin in the intact cell. Enhance d activation of erythrocyte calpain and degradation of calpastatin occ ur under conditions of increased cellular Ca2+ and in cells of the age d.