NCX1 overexpression induces progressive skeletal-muscle pathology. (A and B) Muscle weight-to-tibia length (MW/TL) ratios measured at 2 and 6 months of age in the gastrocnemius (Gastr.) and quadriceps (Quad). *, P < 0.05 versus NTG. (C) Representative hematoxylin and eosin (H&E)-stained histological sections from NCX1 TG and NTG mice at 2 (×200 magnification), 6 (Masson's trichrome; ×100 magnification), and 15 (H&E; ×40 magnification) months of age. (D and E) Results of hydroxyproline assay to measure collagen contents of quadriceps from NTG and NCX1 TG mice at 2 and 6 months of age. *, P < 0.05 versus NTG mice. (F and G) Percentages of fibers with centrally localized nuclei at 2 and 6 months of age in NCX1 TG and NTG histological sections from the indicated muscles. *, P < 0.05 versus NTG mice. (H) Percentages of fibers with centrally localized fibers in 6-month-old FDB muscles from NTG and NCX1 TG skeletal muscle. *, P < 0.05 versus NTG mice. (I) Calpain activity measured by luciferase assay at 3 months of age in the indicated muscles from NTG and NCX1 TG mice. *, P < 0.05 versus NTG mice. The error bars indicate SEM.