FIG. 4.

Large structural defects in the myocardium after mechanical injury. (A, B) Scanning electron microscopy analysis of newt hearts reveals a small ventricular lumen and a compact trabeculated myocardium with a smooth surface. Individual trabeculae cross the ventricle. (C, D) At 1 dpi, a partial loss of cardiac tissue and a decrease in size of trabeculae in the injured region are apparent. (E, F) Large structural defects are visible at 7 dpi. The size of the remaining trabeculae is reduced, exposing the nuclei of subjacent cells (red arrows indicate thin trabeculae after 1 and 7 dpi). (G, H) At 14 dpi, tissue defects are still apparent. Parts of trabeculae in the border zone (bz) have regained a normal morphology, while the surface of trabeculae in the injured zone (iz) still show off the nuclei of underlying cells (red arrows indicate the cells under the surface of trabeculae in the injured region) (I, J) At 21 dpi, subjacent cells are still visible at the surface of the trabeculae, but the overall trabecular surface has smoothened. The injured region is replenished with cardiac tissue, but still shows gaps. (K, L) At 120 dpi, the myocardium shows a compact organization. No significant differences compared to the control hearts are evident. Red dashed lines indicate the injured region; scale bar: (A, C, E, G, I, K) 500 μm; (B, D, F, H, J, L) 50 μm.