Electron Microscopic Studies of Satellite Cells in the Cardiac Muscle of Brachyura

Abstract

The fine structures of c ertain cells found in the peripheral region of the cardiac muscle fiber of two kinds of marine crabs.Chionoecetes opilio and Charybdis japoniza, have been, examined in detail, and these cells have been proved to be identical with th e satellite cells described in vertebrate skeletal muscle fiber. The 180 M. Midsukami following features have been o bserved.
1. The striking paucity o f cytoplasm relative to its nucleus causes the cell to assume the shape of the nucleus.
2. The satellite cell is wedged between the plasma membrane and the basement membrane of the muscle fiber. The surface of the muscle fiber is not distorted outward, but instead this cell protrudes inward pushing aside the components of cardiac muscle cell.
3. On the outside surface of this cell, for most of its cour s e, the plasma membrane lies just beneath the basement membrane of the sarcolemma, where it is not reflexed into the cytoplasm. On the inside surface, some desmosomal structures are occasionally seen between the plasma membrane of the satellite cell and that of the cardiac muscle cell.
4. Numerous particles, a few small mitochondria and some vesicles are seen in this cell.
5. Of greater interest is the evidence that the cells are identical in morphology with the undifferentiated pericytes surrounding blood vessels.