Figure 1.

Distribution of surviving cardiac myocytes in a representative 1-week-old transmural post-MI scar visualized with Masson’s trichrome stain (dark red color in A) and double immunofluorescence staining (B–D) with antibodies against cardiac MHC β-isoform (red color) and laminin (green color). In C and D, nuclei are counterstained with DAPI (blue color). (A) Transverse section through the midventricular level of the post-MI heart demonstrating the presence of viable cardiac myocytes in subendocardial (arrows) and subepicardial (arrowheads) regions of the scar. Note that muscle-specific staining (dark red color) seen within the middle region of the scar is associated entirely with the remnants of dead mummified myocytes. (B) Immunofluorescence micrograph of the area outlined by a black box in A showing the viable cardiac myocytes in subendocardial (arrows) and subepicardial (arrowheads) regions of the same scar obtained on an adjacent serial section. Note that remnants of dead mummified myocytes located in the middle region of the scar remain unstained with antibody against cardiac MHC β-isoform (red color), although most of them continue to be outlined by laminin-positive basement membranes. (C) High-power view of the subendocardial region outlined by a white box in B demonstrating the arrangement of viable cardiac myocytes in the discontinuous layer just beneath the endocardium (arrows) as well as in the isolated cluster around a small, thin-walled venous-like vascular channel, which resembles a Thebesian vein or vessel (asterisk). (D) High-power view of the subepicardial region outlined by a white box in B showing the groups of viable cardiac myocytes beneath the epicardium (white dotted line) in close proximity to a large subepicardial vein (V). Scale bars are 600 µm (A, B) and 50 µm (C, D). Abbreviations: MI, myocardial infarction; MHC, myosin heavy chain; DAPI, 4′,6-diamidino-2-phenylindole.