PKCδ negatively regulates mouse platelet aggregation in response to collagen. (A) Washed platelets were prepared from wild-type or PKCδ^–/– mice and pretreated either with rottlerin (5 μM) for 15 minutes or DMSO vehicle as control. Platelet aggregation was induced with collagen (30 μg/mL) and monitored by turbidimetric aggregometry over a 10-minute period. Traces shown are representative of 3 independent experiments. (B) Whole cell lysates from PKCδ^–/– and wild-type mouse platelets were analyzed for the expression of PKCα, PKCβ, PKCδ, PKCϵ, and PKCθ by immunoblotting (top panels). Uniformity of protein loading was confirmed by immunoblotting with anti–β-tubulin antibody (bottom panels). The immunoblots are representative of 3 independent experiments.