Morphological changes across the border zone of cat hearts subjected to regional ischaemia.

The left anterior descending coronary artery (LAD) was ligated for 3 h in six open chest cats. Six biopsies for electron microscopy were collected from the normal, the ischaemic and the border zones as defined by in vivo injection of fluorescein and as verified by blood flow measurements. Across the fluorescein demarcation line, we collected 3 mm long border zone biopsies, extending 1.5 mm in both the normal and the ischaemic direction. Starting from the normal end twenty subsequent areas (165 microns apart) were studied. By examining a total number of 5280 myocytes we observed an abrupt increase in the number of cells with sarcolemmal fragmentation. This point called border line is accompanied by an abrupt increase in the number of cells with chromatin clumping or margination, and of cells which are mainly necrotic with a massive cytoplasmic oedema. Morphometric analysis of 576 micrographs indicates a border zone on both sides of the border line. The border zone is characterized by a larger fractional volume of mitochondria (extending 1.5-2.0 mm in the normal direction) and by a larger lipid droplet accumulation (extending 1.2 mm or less in the normal direction) than seen in the ischaemic zone. These changes are in the normal part of the border zone accompanied with a moderate cytoplasmic oedema and a fragile sarcolemma with focal disruptions.