Microvasculature and loose connective tissue in freeze-fracture preparations

Summary Tissues of the young chick and chick embryo were prepared in a relatively unaltered condition by the freeze-fracture technique. The ultrastructure of the microvasculature and surrounding interstitial region is compared with that seen in conventional thin-sectioned material. In the undifferentiated vessels of the 3-day chick embryo, no distinct basement lamina can be distinguished in either type of preparation. In the 3-week chick, a continuous basement lamina is present beneath the endothelium only in chemically fixed and sectioned tissue; it cannot be distinguished from the remaining interstitial substance in freeze-fracture preparations. Blood-tissue exchange may depend on permeability characteristics of the entire interstitial region rather than on the basement lamina alone.Work supported by the U.S. Atomic Energy Commission.We acknowledge the services of George T. Chubb and Paul W. Ellwanger in maintaining the electron microscope center.