Endothelial cell “swelling” in ischaemia and reperfusion

The endothelial cells of cardiac capillaries have been reported to swell as a result of ischaemia and reperfusion although there has not previously been any attempt to quantify this observation. Whole capillary and luminal cross-sectional areas, abluminal and luminal membrane lengths were measured from electron micrographs of isolated rat hearts subjected to 30 or 60 min of global ischaemia both with and without subsequent reperfusion for 15 min. All the experimental protocols resulted in capillaries which appeared swollen by electron microscopy. Measurements, however, showed that, after 30 and 60 min ischaemia, this appearance was brought about by a decrease in both whole capillary and luminal area causing an increase in the distance between abluminal and luminal membranes without any change in the endothelial cell cross-sectional area. Reperfusion after 30 min caused an increase in capillary dimensions to larger than control levels. Only after 60 min ischaemia with reperfusion were the cells really swollen with an increase in cross-sectional area. We conclude that (1) we may be observing capillary constriction and (2) the word “swelling” in this context should be used with caution.