Studies on blood vascular silver-blackened fibers (SF, BSF) related to heart beat and vascular phenomenon in vertebrates. IV. Electron-microscopical structure of silver-blackened fibers(SF) of the heart.

Abstract

A specific type of fibers distributed in the cardiac muscle, which can be demonstrated by KAWAHARA's silver staining method No. 4 (1952), were examined by the electron microscope to clarify their fine structure, the process of fiber formation, and their terminations.1. In the heart at an early stage of embryonic life where no cardiac muscle has been developed as yet, fiber-forming particles of low electron density were connected with one another into chains in the interstices of the cardiac tissue observed in electron photo-micrographs. No reticular fibers appear in this stage of development (methods of BIELSCHOWSKY and PAP). When examined by the electron microscope, none of the fibers in question exhibited such basic periodicity as observed in the collagenous fibrils. Therefore, it may well be that those fibers are different from collagenous and reticular fibers.2. In the stage of development of the cardiac muscle (in embryos and adults), it is difficult to confirm the presence of the fibers even by electron microscopy. When the silver-blackening method is applied to the cardiac muscle, however, the peripheral and terminal portions of the fibers in the architectonic of the cardiac muscle can be recognized even in this stage.3. These fibers are of low electron density. When silver-treated, they are recognized as beads of silver particles deposited in the interstices of the cardiac tissue.4. The terminations of the fibers are mostly located in the sarcolemma and are represented by a fine network or branching structure, both of which are formed by chains of silver particles of high electron density and a fiber-forming substance of low electron density.5. In ultra-thin sections, the trunks of our fibers appear only discontinuous. The silver particles deposited on the fibers are arranged chiefly along the long axis of the fibers. The intervals between silver particles deposited on these fibers were relatively narrow.6. None of the fibers in question showed periodic structure as in the collagenous fibrils. They were also distinguished from lattice fibers by using our silver staining method. By employing our silver staining method, the fibers in question were observed in the myocardium of the heart in the earliest stage of embryonic life.