Lysosomal alterations in autolyzing rabbit heart

Abstract

Sequential biochemical and immunohistochemical lysosomal alterations were assessed in autolyzing ventricular myocardium incubated at 37°C in a humidified atmosphere for 15 min to 2 h. A profound redistribution of cathepsin D activity into the nonsedimentable fraction of homogenates could be demonstrated after only 15 min of autolysis, with further increases over the next 105 min. Nonsedimentable activity of n-acetyl-β, d-glucosaminidase was also significantly increased early after the onset of autolysis, but the distribution of acid phosphatase activity was not significantly altered. Immunohistochemical localization of cathepsin D revealed dramatic loss of granular staining in myocytes during the first hour of autolysis. Between 15 and 30 min, lysosomes became enlarged and halos of fluorescent material appeared, representing diffusion of cathepsin D from lysosomes into the myoplasm. By 60 min most cathepsin-D-positive organelles had vanished and the enzyme was instead distributed diffusely throughout the cell. The early redistribution of cathepsin D observed by biochemical and immunohistochemical techniques occurred before electron microscopic indications of cell death became apparent. Thus, autolyzing heart may provide a useful model for studying the possible role of lysosomal enzymes in provoking myocardial cell injury and necrosis.