In vitro and in vivo rapamycin treatment normalizes STIM1 and ORAI1 expression and SOCE in Col6a1^−/− Mks. (Ai) Western blot for STIM1 and ORAI1 in WT and Col6a1^−/− differentiated Mks, in the presence of 100 nM rapamycin (Rapa) or vehicle alone as control (0.1% DMSO). β-Actin was used as a loading control. (Aii) Band densities were quantified and expressed relative to control. Data are mean ± SD (n = 5). 1-way ANOVA. (Bi) Representative Fura-2 fluorescence ratios reflecting [Ca²⁺]_i variations in WT and Col6a1^−/− differentiated Mks, in the presence of 100 nM Rapa or vehicle alone. Ca²⁺ flows were monitored in the presence of 10 μM CPA in Ca²⁺0 conditions and after the addition of 1.5 mM extracellular Ca²⁺. (Bii) Analysis of Ca²⁺ flows (ER release and SOCE) in WT and Col6a1^−/− Mks. A minimum of 40 Mks were analyzed per experiment. Data are mean ± SEM (n = 4). 1-way ANOVA. (C) Flow cytometry analysis of STIM1 and ORAI1 protein expression in BM Mks from WT and Col6a1^−/− mice treated with Rapa (2 mg/kg body weight) or vehicle as control (5% PEG-400/5% Tween-80 in saline). Data are mean ± SD (n = 5). 1-way ANOVA. (Di) Western blot for STIM1 and ORAI1 in platelets from WT and Col6a1^−/− mice treated with Rapa or vehicle as control. (Dii) Band densities were quantified and expressed relative to control. Data are mean ± SD (n = 5). 1-way ANOVA. (E) Flow cytometry analysis of integrin αIIbβ3 activation (JON/A antibody binding) in WT and Col6a1^−/− platelets, after stimulation with thrombin (0.1 U/mL), from mice treated with Rapa or vehicle as control. Data are mean ± SD (n = 5). 1-way ANOVA. (F) Peripheral blood platelet (Plt) count in WT and Col6a1^−/− mice following administration of Rapa or vehicle as control (n = 3). Data are mean ± SD (n = 3). 1-way ANOVA. *P < .05, **P < .01. CTRL, control; MFI, mean fluorescence intensity.