Calpain, septin-5, and platelet secretion. (A) Effect of calpain activation on the association of septin-5 with syntaxin-4 (Synt 4) in human platelets. (B) Levels of serotonin (5-HT) and TGF-β (ELISA) released from human platelets stimulated with either thrombin (Thr, 1 U/mL) or thrombin plus Ca²⁺ (to activate calpain). Experiments were performed in the absence and presence of calpeptin (Cpt, 10μM). (C) CCL5 levels in releasate from unstimulated and thrombin-stimulated platelets without and with calpain activation with Ca²⁺. Experiments were performed in the absence or in the presence of calpeptin (Cpt). (D) Effect of diabetes on CCL5 levels (ELISA) in plasma from healthy subjects and from patients with type 2 diabetes. (E) Immunostaining of CCL5 (red) released from platelets (β3 integrin [green]) onto endothelial cells (DAPI; white). Platelets were either left unstimulated (CTL) or treated with Ca²⁺ in the absence or in the presence of calpeptin (Cpt). Bars represent 20μM. The graphs summarize data obtained with 5-6 subjects per group. *P < .05, **P < .01, ***P < .001 versus CTL/Sol/Healthy.