Col6a1^−/− platelets and Mks have increased STIM1 and ORAI1 expression and increased SOCE. (Ai) Western blot for STIM1 and ORAI1 in WT and Col6a1^−/− platelets. β-Actin was used as a loading control. (Aii) Band densities were quantified and expressed relative to WT. Data are mean ± SD (n = 6). Student t test. (Bi) Representative FLUO3 fluorescence–based [Ca²⁺]_i traces of WT (red line) and Col6a1^−/− (blue line) platelets incubated in Ca²⁺0 conditions. Where indicated, successive additions of 5 µM thapsigargin (TG) and 1 mM Ca²⁺ were carried out. (Bii) Quantification of basal and peak [Ca²⁺]_i following the addition of thapsigargin (ER release) and Ca²⁺ (SOCE) in WT and Col6a1^−/− platelets. Data are mean ± SEM (n = 5). Student t test. (Ci) Quantitative RT-PCR analysis of STIM1 and ORAI1 mRNA expression in sorted BM Mks from WT and Col6a1^−/− mice. Data are mean ± SD (n = 3). Student t test. (Cii) Flow cytometry analysis of STIM1 and ORAI1 protein levels in BM Mks from WT and Col6a1^−/− mice. Data are mean ± SD (n = 4). Student t test. (Di) Representative Fura-2 fluorescence ratios reflecting [Ca²⁺]_i in WT and Col6a1^−/− differentiated Mks. [Ca²⁺]_i variations were monitored in the presence of 10 μM CPA in Ca²⁺0 and after addition of 1.5 mM extracellular Ca²⁺. (Dii) Analysis of Ca²⁺ flows (ER release and SOCE) in WT and Col6a1^−/− Mks. Data are mean ± SEM (n = 4). Student t test. *P < .05, **P < .01.