Ultrastructural changes at the border of the ischaemic zone within one hour of coronary artery occlusion.

The ultrastructure was studied by electron microscopy in myocytes obtained from the periphery of the ischaemic zone 10, 20, 40, and 60 min after occlusion of the left anterior descending coronary artery (LAD) in open chest anaesthetized cats. The morphology of this zone was compared to that of the normally perfused myocardium in the same hearts. Samples were collected from the border of the ischaemic tissue as defined by in vivo injection of fluorescein and verified by regional blood flow measurements with radiolabelled microspheres. After 10 min of LAD-occlusion, we observed swelling of the mitochondria in the border zone. The mitochondrial swelling remained stable for the first hour after LAD-occlusion. There was no difference in the fractional volume of lipid droplets between the normal and border zones after 10 min of ischaemia. The fractional volume of lipid droplets, however, was significantly reduced in the normal zone after 20 min of coronary artery occlusion, whereas it remained unchanged in the border zone. Up to 60 min after LAD-occlusion the fractional volumes of cytoplasm in the border zone were not different from the corresponding values in the normal zone, indicating that there was no cytoplasmic oedema in the border zone. However, a reduced fractional volume of myofibrils in the border zone after 20 min of LAD-occlusion, may indicate a slight cell swelling, probably due to the mitochondrial swelling. In the border zone there was a slight increase in the number of cells with sarcolemmal injuries after 10 min of LAD-occlusion. Cells with chromatin clumping and margination were found after 20 min.(ABSTRACT TRUNCATED AT 250 WORDS)