MYOCYTE INJURY BY HEMIN

Effects of free hemin on myocardium were investigated using a model of neonatal myocyte primary cultures. Cells were subjected to free hemin at concentrations up to 20 muM and equilibrated for 5 h at 37-degrees -C. Distribution of hemin in media, cell sarcolemma, and cell interior was evaluated. Time-dependent reduction in beating rate was monitored throughout the entire concentration range of administrated hemin. Wit h time and in a hemin concentration-dependent manner, arrhythmic beati ngs which were followed by loss of contractility were observed. In par allel, morphologic changes appeared from granulation to complete loss of cell integrity. At the concentration range studied, hemin also indu ced a biphasic release of cytosolic enzymes. In the first phase, the f raction of enzyme released was dependent of the ratio of hemin:cells a nd was correlated with the amount of nonviable cells as monitored by a trypan blue test. In the second phase, the fraction of released enzym e was much larger than that of nonviable cells. The data are interpret ed as an indication of complete loss of cytosolic content due to sarco lemma damage in first phase and partial damage to cell interior in the prolonged second phase. It is concluded that in similarity with other amphipathic molecules, free hemin is toxic to the myocardium.