APOPTOTIC MYOCYTES IN INFARCT AREA IN RABBIT HEARTS MAY BE ONCOTIC MYOCYTES WITH DNA FRAGMENTATION - ANALYSIS BY IMMUNOGOLD ELECTRON-MICROSCOPY COMBINED WITH IN-SITU NICK END-LABELING

Background - Modes of cell death have been defined morphologically as apoptosis and oncosis. Infarcted myocytes have been reported to show a poptosis, as revealed by DNA fragmentation by DNA ladder and by in sit u terminal deoxynucleotidyl transferase-mediated dUTP nick end-labelin g (TUNEL) at the light microscopic level. We investigated whether TUNE L-positive infarcted myocytes have apoptotic or oncotic ultrastructure s by using electron microscopic TUNEL, which can simultaneously observ e the ultrastructure and DNA fragmentation of the same myocytes. Metho ds and Results - Thirty rabbits were divided into 5 groups (n=6 each) that were subjected to a sham operation or to 30-minute ischemia follo wed by 0-minute, 30-minute, 2-hour, or 4-hour reperfusion of a coronar y artery, In the 2- and 4-hour reperfusion groups only, DNA electropho resis showed a ladder pattern, and the light microscopic TUNEL finding was positive in the nuclei of myocytes localized in the infarcted are a (6 +/- 2% and 11 +/- 3%, respectively). Electron microscopic TUNEL s howed that nuclei with a significant accumulation of immunogold partic les (indicating an electronic microscopic TUNEL-positive result) were observed only in the infarcted myocytes with irreversibly oncotic ultr astructures that were found in the hearts of the 2- and 3-hour reperfu sion groups (41 +/- 3% and 83 +/- 4%, respectively). Irreversibly onco tic myocytes (indicated by swelling, inhomogeneously clumped chromatin in nuclei, dense bodies in mitochondria, and/or ruptured plasma membr anes) were also seen in the 0- and 30-minute reperfusion groups, which did not exhibit TUNEL-positive myocytes. There was no evidence of apo ptotic ultrastructures in the myocytes. Conclusions - DNA fragmentatio n occurs in the myocytes that had already shown irreversibly oncotic, but not apoptotic, ultrastructures with ischemia and/or reperfusion. T herefore, DNA fragmentation itself does not always mean apoptosis, and so-called apoptotic infarcted myocytes may belong to a category of ce ll death other than apoptosis.