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Calpain‐mediated breakdown of cytoskeletal proteins contributes to cholecystokinin‐induced damage of rat pancreatic acini

The cytosolic cysteine protease calpain is implicated in a multitude of cellular functions but also plays a role in cell damage. Our previous results suggest that an activation of calpain accompanied by a decrease in its endogenous inhibitor calpastatin may contribute to pancreatic damage during cerulein‐induced acute pancreatitis. The present study aimed at the time course of secretagogue‐induced calpain activation and cellular substrates of the protease. Isolated rat pancreatic acini were incubated with a supramaximal concentration of cholecystokinin (0.1 μM CCK) for 30 min in the presence or absence of the calpain inhibitor Z‐Val‐Phe methyl ester (100 μM ZVP). The activation of calpain and the expression of calpastatin and the actin cytoskeleton‐associated proteins αII‐spectrin, E‐cadherin and vinculin were studied by immunoblotting. The cell damage was assessed by lactate dehydrogenase release and ultrastructural analysis including fluorescence‐labelled actin filaments. Immediately after administration, CCK led to activation of both calpain isoforms, μ‐ and m‐calpain. The protease activation was accompanied by a decrease in the E‐cadherin level and formation of calpain‐specific breakdown products of αII‐spectrin. A calpain‐specific cleavage product of vinculin appeared concomitantly with changes in the actin filament organization. No effect of CCK on calpastatin was found. Inhibition of calpain by ZVP reduced CCK‐induced damage of the actin‐associated proteins and the cellular ultrastructure including the actin cytoskeleton. The results suggest that CCK‐induced acinar cell damage requires activation of calpain and that the actin cytoskeleton belongs to the cellular targets of the protease.