Differential expression patterns of regulatory and catalytic subunits of PI3K class IA and their kinase activities in platelets from p85α—/— and wild-type mice. (A-B) Expression patterns of regulatory subunits of PI3K class IA in wild-type hematopoietic organs (A) and in platelets from wild-type p85α+/+, p85α+/–, and p85α–/– mice (B), shown by Western blot with αp85^PAN. (C-D) The amount of p85β protein in platelet lysate and its immunoprecipitate with anti-p85^PAN antiserum (C) and the amount of p110 catalytic subunits (p110α,p110β, and p110δ) in platelet lysate from p85α+/+ and p85α–/– mice (D), shown by Western blot with p85β-specific antiserum and anti-p110 polyclonal antibodies, respectively. Whole-cell lysate (50 μg per lane) or its immunoprecipitate was resolved using SDS-PAGE. (E) PI3K activity of wild-type and p85α–/– platelets measured using anti-p85^PAN antiserum and resolved by thin-layer chromatography. The wild-type response was set to 100% and the activity of p85α–/– platelets was estimated to be 5% of the wild-type response.