Two unusual satellite cell-intrafusal muscle fiber relationships.

Abstract

We studied the location and ultrastructure features of rat teres minor intrafusal muscle fiber satellite cells. They were abundant in myotube and polar regions, particularly near sensory nerve terminals and terminations of the spindle capsule and intrafusal muscle fibers. One satellite cell was wedged between two “paired” nuclear bag fibers in the myotube region. No basement membrane surrounded this cell. A polar satellite cell was encased by the basement membrane for only part its length. This cell contained numerous myofilaments. It terminated in the intercellular space surrounded by its own basement membrane adjacent to the host nuclear bag fiber. Recent satellite cell investigations are summarized and compared with the results of this study. We conclude there may be more than one cell type in the satellite cell position and intrafusal and extrafusal satellite cells may function in different capacities.