Figure 2A Cardiac function evaluated by echocardiography in mdx/CD38-/- mice: the dot plots show the left ventricular (LV) diastolic (A1) and systolic (A2) inner diameters and LV ejection (A3) fraction in 7-month-old WT (n=5), mdx (n=6) and mdx/CD38-/- (n=10) mice. Data information: : Each dot of the graphs represents a mouse. in duplicate After normality and variance comparison tests, significance was assessed using:A1 ANOVA followed by Fisher's LSD test; A2,A3 Kruskal-Wallis followed by Dunn's test; Values are expressed as means ± SEM. Significance: *p<0.05, **p<0.01, ***p<0.001. B Plasma levels of cardiac stress biomarkers: brain natriuretic peptide (BNP) (B1) and cardiac troponin I (cTnI) (B2) in 7-month-old WT (n=7), mdx (n=6) and mdx/CD38-/- (n=11) mice. Data information: : Each dot of the graphs represents a mouse. After normality and variance comparison tests, significance was assessed using ANOVA followed by Fisher's LSD test; Values are expressed as means ± SEM. Significance: *p<0.05, **p<0.01, ***p<0.001. C Cropped images revealed the collagen (blue) stained by Masson's trichrome staining in the heart of WT, mdx, and mdx/CD38-/- mice. Dot plot showing the quantification of heart collagen staining area (% total area) in 7-month-old WT, mdx, and mdx/CD38-/- mice (n=4 per group). Scale bars: 200 µm. Data information: : Each dot of the graphs represents a mouse. in triplicate After normality and variance comparison tests, significance was assessed using ANOVA followed by Fisher's LSD test Values are expressed as means ± SEM. Significance: *p<0.05, **p<0.01, ***p<0.001. D Isoproterenol-induced heart failure in 3-month-old mice. The Kaplan-Meier curve shows the survival rate of mdx mice (NaCl, n=5); mdx (n=19) and mdx/CD38-/- (n=9) mice following isoproterenol (subcutaneous injection) at 2.5 mg/kg/d for 10 days. Data information: one value/mouse. After normality and variance comparison tests, significance was assessed using D: Log-rank Mantel-Cox test and Log-rank test for trend and Gehan-Breslow-Wilcoxon test ; Values are expressed as means ± SEM. Significance: *p<0.05, **p<0.01, ***p<0.001. E Histogram showing isoproterenol-induced heart hypertrophy in mdx NaCl (n=5) mice, surviving mdx (n=9), mdx/CD38-/- NaCl (n=9) and mdx/CD38-/- (n=9) mice, expressed as heart weight/body weight ratio (HW/BW). Data information: one value/mouse. After normality and variance comparison tests, significance was assessed using Kruskal-Wallis followed by Mann-Whitney tests Values are expressed as means ± SEM. Significance: *p<0.05, **p<0.01, ***p<0.001. F Plasma levels of cardiac stress biomarkers: brain natriuretic peptide (BNP) (F1) and cardiac troponin I (cTnI) (F2) following isoproterenol treatment in mdx NaCl (n=5), surviving mdx (n=8), mdx/CD38-/- NaCl (n=5) and mdx/CD38-/- (n=8) mice. Data information: in duplicate After normality and variance comparison tests, significance was assessed using F2 Kruskal-Wallis followed by Mann-Whitney tests; F1: ANOVA followed by Student's/ Welch's t-tests; Values are expressed as means ± SEM. Significance: *p<0.05, **p<0.01, ***p<0.001. G,H Time-lapse images recorded by confocal microscopy in "line scanning mode", showing Ca2+ sparks and waves in cardiomyocytes at rest, extracted from mdx and mdx/CD38-/- mice; scale bars: 10 µM (horizontal), 500 ms (vertical). Bar graphs showing the averaged Ca2+ sparks (G) and waves (H) frequencies in cardiomyocytes isolated from WT (n=21 cells), mdx (n=28 cells) and mdx/CD38-/- (n=32 cells) mice. Data information: experiments performed in 3 mice of each group. After normality and variance comparison tests, significance was assessed using Kruskal-Wallis followed by Dunn's test; Values are expressed as means ± SEM. Significance: *p<0.05, **p<0.01, ***p<0.001. I Bar graph showing the fractional release following caffeine application in cardiomyocytes from WT (n=24 cells), mdx (n=33 cells) and mdx/CD38-/- (n=32 cells) mice. Data information: experiments performed in 3 mice of each group. After normality and variance comparison tests, significance was assessed using: ANOVA followed by Fisher's LSD test; ; Values are expressed as means ± SEM. Significance: *p<0.05, **p<0.01, ***p<0.001. J Bar graph showing the post-rest potentiation in cardiomyocytes from WT (n=24 cells), mdx (n=28 cells) and mdx/CD38-/- (n=32 cells) mice. Data information: experiments performed in 3 mice of each group. After normality and variance comparison tests, significance was assessed using: Kruskal-Wallis followed by Dunn's test Values are expressed as means ± SEM. Significance: *p<0.05, **p<0.01, ***p<0.001.