Myocyte swelling and plasmalemmal integrity during early experimental myocardial ischemia in vivo

Abstract

Using scanning and transmission electron microscopy, the structure of myocytes early in the phase of irreversible injury induced by 40 minutes of severe regional ischemia has been investigated, paying particular attention to the effects of cell swelling on the SEM appearance of the myocytes. Swollen myocytes showed an increased space beneath the plasmalemma and between organelles. True subsarcolemmal blebs were not seen and the attachment complexes between the Z-band and the underlying myofibrils remained intact. The proportion of the PS face of the plasmalemma which appeared "en face" (0.70%, SD:1.22 vs 5.01%, SD:3.72) in freeze-fracture faces of ischemic tissue was increased significantly. The increase may be due to swelling of the cell in the subplasmalemmal space or may be mediated through structurally unapparent alterations in the cytoskeleton. The PS face showed frequent longitudinal shifts in the alignment of Z band - plasmalemmal attachment between adjacent myofibers. T-tubule ostia, caveolae and junctional SR were demonstrable on the PS face. With standard preparative methods and instrumentation, no discrete fibrillar network associated with Z band attachment or subjacent to the plasmalemma was detected and there was no direct structural evidence of cytoskeletal alteration as a result of ischemic injury. Osmium-ligand preparation of tissue samples resulted in less damage induced by the electron beam, but did not allow significantly better resolution.