Tail suspension induces calpain activation, myocardial atrophy, and dysfunction in mice. Adult male mice were subjected to tail suspension for 14 or 28 days. A, hind limb muscle mass. Data are mean ± S.D. (error bars), n = 5–7 in each group. One-way ANOVA followed by Newman–Keuls test was performed for statistical analysis (F = 59.01, p < 0.0001). *, p < 0.05 versus sham. B, calpain activities in heart tissues from Capns1-KO mice and their WT littermates. Data are mean ± S.D., n = 6 in each group. Two-way ANOVA followed by Newman–Keuls test was performed for statistical analysis (interaction, F = 19.27, p < 0.0001; row factor, F = 33.81, p < 0.0001; column factor, F = 56.78, p < 0.0001). *, p < 0.05 versus sham; †, p < 0.05 versus 14 days after tail suspension in WT; #, p < 0.05 versus 28 days after tail suspension in WT. C, the ratio of heart weight relative to tibia length. Data are mean ± S.D., n = 5–7 in each group. One-way ANOVA followed by Newman–Keuls test was performed for statistical analysis (F = 75.13, p < 0.0001). *, p < 0.05 versus sham; †, p < 0.05 versus 14 days after tail suspension. D, fractional shortening (%) was analyzed by echocardiography. Data are mean ± S.D., n = 5–7 in each group. One-way ANOVA followed by Newman–Keuls test was performed for statistical analysis (F = 32.44, p < 0.0001). *, p < 0.05 versus sham; †, p < 0.05 versus 14 days after tail suspension. E, top, a representative staining of wheat germ agglutinin in heart tissue sections; bottom, quantitation of cardiomyocyte cross-sectional area. Data are mean ± S.D., n = 5–6 in each group. One-way ANOVA followed by Newman–Keuls test was performed for statistical analysis (F = 100.8, p < 0.0001). *, p < 0.05 versus sham; †, p < 0.05 versus 14 days after tail suspension.