Electron micrographs from E18.5 urinary bladder strips. Upper panels: Longitudinal section. Middle panels: Cross section of intact bladder strips. Lower panels: Longitudinal section of skinned bladder strips. Images of smooth muscle cells showed glycogen particles (G), well developed mitochondria (M), and caveolae (Cav) alternating with dense bands along the plasma membrane in both intact Cald1^+/+ and Cald1^−/− fetuses. Filaments were present in the cytoplasm, but the conservation of actin and myosin (My) filaments was not sufficient to discern differences between Cald1^+/+ and Cald1^−/− bladder smooth muscle.