[Electron microscope studies of the structure and junctions of heart and skeletal muscle capillaries in the rat...

Comparative investigations with freeze etching procedure of capillaries of the rat heart and triceps muscle (fetal and some postnatal stages) reveal some differences of the junctional structures. Junctions of the skeletal muscle capillaries show several parallel arranged rows of partly linked and interrupted junctional strands with relative few junctional particles. In the 3rd week of life, we found also short fragments of non parallelized strands densely covered with particles which could be related to the venous segment of the capillary. The junctions of myocardial capillaries show a reduced number of mostly zigzag-like arranged junctional strands with many particles and large non sealed gaps. Areas with extremely reduced strands were kept for the venous segments. The above described differences could be responsible for the better permeability of the heart capillaries to horse radish peroxidase.