CALPAIN ACTIVATION IN SHEAR-INDUCED PLATELET-AGGREGATION

Fluid shear stress has been known to activate platelet reaction such a s aggregation, but the exact mechanism of shear-induced platelet aggre gation (SIPA) has not been fully understood. Calpain, an intracellular calcium-activated cysteine protease, is abundant in platelets and is considered to be activated and involved in the proteolytic processes d uring platelet activation. A possible activation of calpain in SIPA wa s investigated, employing a newly developed aggregometer and specific monoclonal antibodies to detect activation of calpain. When a shear st ress gradient varying between 6 and 108 dyn/cm(2) was applied to plate lets, activation of mu-calpain was observed only in high-shear-stresse d platelets, resulting in the proteolysis of talin. At 1 min after the onset of constant high shear stress of 108 dyn/cm(2), mu-calpain acti vation and proteolysis of talin were detected and increased in a time- dependent manner. Constant shear stress more than 50 dyn/cm(2), applie d for 5 min, caused mu-calpain activation and proteolysis of talin, wh ich were increased in a shear-force-dependent manner. Calpeptin, a cal pain-specific peptide antagonist, caused the complete inhibition of bo th mu-calpain activation and proteolysis of talin, while SIPA profiles with calpeptin showed almost no change compared to those without calp eptin. These results suggest the possibility of calpain involvement in late phases of shear-induced platelet activation such as cytoskeletal reorganization. (C) 1997 Wiley-Liss, Inc.