An Electron Microscope Study of Embryonic Heart Muscle Cells Grown in Tissue Cultures

Abstract

Heart muscle of chick embryos 5-9 days old was maintained in tissue cultures, and the fine structure of the embryonic heart muscle was described as it appeared in thin sections of these cultures under the electron microscope. Myofibrils were found in the heart muscle cells even after more than 30 days of cultivation. They do not have the rigid parallel course that they have in preparations of the uncultured heart muscle, but their position changes according to the movements of the migrating cells. Also their structure is more simple than in preparations which have been obtained by other investigators from the uncultured heart. They always show the telephragm Z and the thin 100-150 A myofilaments which run from one Z to another. In uncontracted fibers I can be distinguished from A, very seldom H or M are observed. The Z band is often enlarged. The very much flattened cells of the growth area offer good conditions for studying the interrelationship of the myofibrils with other components of the sarcoplasm. No direct contact with the mitochondria was found. The Z band appears independent of the structures in the sarcoplasm, but a few images were obtained where it seems to be structurally related to the endoplasmic reticulum. In highly extended cells of the growth area only fragments of myofibrils are found consisting of one or two Z- bands and bushels of free ending filaments. These images seem to indicate a loss of structure, a de-differentiation of the muscle cells in culture.