Sequential lysosomal alterations during cardiac ischemia. I. Biochemical and immunohistochemical changes

Ligation of the circumflex artery of rabbit hearts produced a sharply defined area of cardiac ischemia. Total activities of cathepsin D, N-acetyl-β,D-glucosaminidase, and acid phoshphatase in ischemic tissue were not altered over the ensuing 2-hour period, but significant changes developed in the distribution of the enzymes between sedimentable (particle-bound) and nonsedimentable (soluble) fractions of the tissue homogenate. Nonsedimentable cathepsin D activity was significantly elevated in ischemic tissue by 15 minutes after occlusion and increased over the next 105 minutes. Increases in nonsedimentable glucosaminidase and acid phosphatase activities were somewhat less marked than that of cathepsin D; statistically significant changes in the distribution of these enzymes appeared at 30 minutes. Unlike cathepsin D and glucosaminidase, changes in acid phosphatase were maximal by 45 minutes, after which further increases in nonsedimentable activity were not apparent. Immunohistochemical staining of cathepsin D in ischemic tissue sections revealed apparent diffusion of the enzyme from discrete organelles into the surrounding cytosol by 30 minutes after occlusion, but not at 15 minutes. These results suggest that: (1) significant alterations in lysosomal properties and enzyme distributions occur early after myocardial ischemia; (2) changes are somewhat heterogeneous for different enzymes; and (3) biochemical evidence of increased lysosomal fragility precedes anatomical evidence of enzyme translocation in the tissue.