An investigation of some properties of endothelium related to capillary permeability

Abstract

The muscle capillaries of hearts taken directly from rats and mice, or perfused in vitro through the coronary vessels, were investigated by electron microscopy. The electron-dense marker particles ferritin and saccharated iron oxide were introduced into the blood or perfusion fluid. Versene, enzymes, surface active agents, and inhibitors of metabolism were added to the perfusion fluid, and perfusion was also carried out at 0 degrees C. Caveolae and vesicles were present in the endothelium of perfused hearts after all these measures; in damaged cells they disappeared in parallel with the cell and nuclear membranes. Particles entered caveolae and vesicles from the lumen under all conditions of perfusion. With saccharated iron oxide it was not certain what proportion of particles entering caveolae from the lumen passed right through the cell, since some of the particles in external caveolae could have come from accumulations in the basement membrane. Small numbers of ferritin molecules seemed to traverse the cell by the caveolae and vesicles in perfused hearts and in the whole animal. Groups or chains of communicating caveolae and vesicles were often seen. The cells remained closely apposed and the junctions intact in all preparations. Saccharated iron oxide passed into the junctions. In perfused hearts a variable amount left the vessels by this route, which was probably the main source of accumulations in the basement membrane and extravascular structures. Very little ferritin entered the junctions either in the intact animal or in vitro. The basement membrane was largely removed by papain and by impure preparations of collagenase but was not clearly affected by the other enzymes used. The removal of calcium from the perfusion fluid caused the basement membrane to separate from the endothelium.