Effect of PTL on action potential properties in WT and mdx cardiomyocytes. (A, C) Typical examples of action potentials (APs) recorded at the stimulation frequency of 2 Hz in WT (A) and mdx (C) cardiomyocytes (CMs). Insets: first derivatives (dV/dt) of the AP upstrokes. (B, D) Average data at 2 Hz for maximal upstroke velocity (V_max), AP amplitude (APA), resting membrane potential (RMP), AP duration at 20, 50, and 90% repolarization (APD₂₀, APD₅₀, and APD₉₀) in WT (B) and mdx (D) CMs after 3–5 h incubation with either DMSO or PTL (10 µM). n represents the number of cells measured. WT: N = 8 mice; mdx: N = 7 mice. **P < 0.01, *P < 0.05, unpaired Student’s t-test or Mann–Whitney test.