Electron microscopy analysis of Neblex3-knockout (KO) mouse hearts while sedentary (A) or after exercise (B). Nebl, nebulette. Scale bar = 500 μm. Bc–Be and Bh-Bj: higher magnifications of the sarcomere, intercalated disks (IDs), and mitochondria (M) in Nebl+/+ (Bc–Be from Aa and Bb) or Neblex3-/ex3- (Bh-Bj from Af and Bg) mice. L, lysosome. Arrows point to normal Z-disks and IDs, double arrows indicate focal mild ID widening, and triple arrows indicate diffuse severe ID disruptions. *Mitochodrial distortion.