TROPONIN-T CROSS-LINKING IN HUMAN APOPTOTIC CARDIOMYOCYTES

Intracellular calcium overload of guinea pig cardiomyocytes is accompa nied by troponin T cross-linking, which is revealed by changes ill imm unoreactivity of anti-troponin T antibodies, We presently investigated whether the same process is detectable in the human heart Immunohisto chemistry shows myofibrillar staining with BN-59 anti-troponin T antib ody with rare cardiomyocytes in samples obtained at surgery, whereas a pproximately 50% of myocytes are labeled in heart samples taken at aut opsy within 3 hours of death, and every cardiomyocyte is stained after exposure of biopsy sections to 10 nmol/L calcium. Western blot analys is shows reactive polypeptides of approximately 70 and 85 to 90 kd in addition to troponin T in both treated and autopsy heart sections, Nei ther reactivity in immunohistochemistry nor additional reactive polype ptides in Western blot are detectable when calpain or transglutaminase is inhibited during exposure of sections to high calcium. Troponin T crosslinking occurs also in isolated myofibrils, which show staining w ith BN-59 at either sarcomeric A or I bands, Labeling with TdT-mediate d dUTP nick end labeling (TUNEL) to demonstrate apoptosis reveals DNA fragmentation in BN-59-positive myocytes. Thus, troponin T cross-linki ng occurs in human cardiac myocytes concomitantly with apoptosis and a utopsy autolysis, suggesting that similar cy cytosolic alterations can be produced by different types of myocyte death.