Defective SOCE in Stim1-deficient platelets. (A) 5-wk-old wild-type and Stim1^−/− littermates. (B) Body weights of wild-type (+/+) and Stim1^−/− (−/−) mice. Values are mean ± SD. ***, P < 0.001. (C) Western blot analyses of platelet lysates from mice with the indicated genotypes (top) or of mice transplanted with the indicated bone marrow (bottom). Stim1 was assessed using an antibody that can recognize the N-terminal region of the protein (GOK/Stim1; reference 11). An antibody to β3 integrin served as control. Results from two individuals per group are shown. (D) Peripheral platelet counts in wild-type and Stim1^−/− mice. Values are mean ± SD. (E) Fura-2–loaded platelets were stimulated with 5 μM TG for 10 min, followed by the addition of extracellular Ca²⁺ and monitoring of [Ca²⁺]_i. Representative measurements (left) and maximal increase in intracellular Ca²⁺ concentrations compared with baseline levels (Δ[Ca²⁺]_i) ± SD (n = 4 mice per group) before and after addition of 1 mM Ca²⁺ (right) are shown. **, P < 0.01; ***, P < 0.001.