(a) Western blot analysis from adult hearts after CELF1 induction. (b) Fractional shortening was measured in MHC (n=6 animals) and TRECUGBP1/MHC mice (n=3 animals) that were given doxycycline (4 days). Results are expressed as the mean±s.e.m. (c) Confocal imaging of T-tubules on living CM from MHC (#1–2; n=2 animals) and CELF1-expressing (#3–4, n=2 animals) mice. Scale bar, 10 μm. Third row: fluorescence plot over the white line on the first row. (d–g) T-tubule and calcium spark analysis: normalized T-tubule power (d) (n=13 cells for MHC animals, n=16 cells for TRCUGBP1/MHC animals), T-tubule area (e) (n=12 cells for MHC animals, n=16 cells for TRCUGBP1/MHC animals), T-tubule irregularity (f) (n=13 cells for MHC animals, n=16 cells for TRCUGBP1/MHC animals), calcium spark frequency (g) (n=11 cells per genotype). *P≤0.05, Student's t-test. Results are expressed as the mean±s.e.m. CELF1 oe: TRECUGBP1/MHC animals. MHC: controls. DIC, differential interference contrast microscopy; FFT, fast Fourier transform; T-tubules, transverse tubules.