Myosatellite cells associated with different muscle fibre types in the Atlantic hagfish (Myxine glutinosa, L.).

The incidence of myosatellite cells associated with "white" and "red" muscle fibres of the parietal muscle and "red" fibres of the craniovelar muscle was estimated by quantitative electron microscopy in the Atlantic hagfish (Myxine glutinosa, L.). Myosatellite cell nuclei constitute 3, 11 and 23% of the total number of nuclei inside the basal lamina of the three types of muscle fibres, respectively. However, the total number of nuclei is highest in "white" fibres, most of the nuclei belonging to striated muscle cells. Myosatellite cell profiles in transverse sections constitute 23, 41 and 61% of the number of muscle fibre profiles of the three types, respectively. The intervals between adjacent myosatellite cells are approximately 135 micrometer in "white" fibres, approximately 55 micrometer in "red" parietal fibres, and only approximately 25 micrometer in craniovelar fibres. Since craniovelar fibres are also comparatively thin, myosatellite cells constitute a significant fraction of the volume inside the basal lamina in these fibres. The myosatellite cells are approximately 30-50 micrometer long and up to 5 micrometer thick. Some myosatellite cells possess few organelles, whereas others appear to contain many free ribosomes, granular endoplasmic reticulum, prominent Golgi apparatus and lysosome-like bodies.