Calpain Activity in Rat Renal Proximal Tubules: An In Situ Assay

Although considerable information about calpain has been obtained from studies using isolated enzyme preparations, this does not permit the dynamic assessment of intracellular protease activity during changes in intracellular Ca²⁺ and pH. Intracellular calpain activity is regulated by complex interactions with the specific inhibitory protein (calpastatin), Ca²⁺ and phospholipids, conditions which are difficult to duplicate in isolated systems. Thus a method to measure calpain activity over time in living cells would be helpful in studying its regulation and physiological roles.