TABLE I. Calpain inhibition blocks platelet aggregation.
The initial slope of thrombin-induced platelet aggregation was compared at varying concentrations of inhibitor. The uninhibited rate of aggregation was determined from peptide vehicle (150 mm HEPES-KOH, pH 7.4), in the case of calpastat and calpastat-Ala, or Me2SO vehicle, in the case of calpeptin, MDL, and E64d. NI indicates that no inhibition of aggregation occurred with calpastat-Ala, at the concentrations used for calpastat, and that no inhibition of aggregation occurred with NH4Cl lysosomal inhibition. Rates of thrombin-induced (0.05 units/ml) aggregation of gel-filtered platelets were measured during the first 15 s of aggregation, immediately following shape change. Thrombin-induced shape change was not affected by any of the inhibitors.
| Inhibitor | IC50 |
|---|---|
| µm | |
| Calpastat | 50 |
| Calpastatin 24-mer | NI |
| Calpastat-Ala | NI |
| Calpeptin | 150 |
| MDL | 240 |
| E64d | 340 |
| NH4Cl (10 mm) | NI |