Rat Cardiomyocytes with TUNEL-Positive Nuclei Induced by Permanent Ischemia Show Increased Plasma-Membrane Perme- ability Monitored by a Combined Use of TUNEL Method and Lanthanum Ions

The aim of this study was to clarify whether myocardial cells with DNA fragmentation induced by ischemia show increased plasma-membrane permeability (PMP), focusing on the early lesions of acute myocardial ischemia (AMI). Rat AMI was induced by a permanent occlusion of the left coronary artery. The TUNEL method was used for the demonstration of DNA fragmentation, and lanthanum ions (La) were employed for the increased PMP of cardiomyocytes. The increased PMP of cardiomyocytes having TUNEL-positive nuclei was determined by a combined use of the TUNEL method in frozen sections and electron microscopic identification of intracellular depositions of La. Seven of 10 cardiomyocytes having TUNEL-positive nuclei revealed the deposition of La 2 hours after ischemia, and 10 of 13 showed La deposition 3 hours after ischemia. Almost all cardiomyocytes labeled with TUNEL stain showed intracellular deposition of La 4 and 6 hours after ischemia, respectively. The evidence obtained from this experiment demonstrates that almost all cardiomyocytes labeled with TUNEL stain simultaneously show an increase of PMP in the AMI foci. In conclusion, the mechanism of myocardial cell death caused by permanent ischemia is due to a mixed form of apoptosis and necrosis.