The Role of Satellite Cells on Adaptatives States of Skeletal Muscle Tissue

Abstract

Skeletal muscle tissue is extremely sensitive to the acute and chronic stresses induced by exercises. Satelite cells are directly involved in processes of regeneration, hypertrophy and hyperplasia in adult muscle tissue. They represent quiescent cells, which are located between the basal lamina and the sarcoplasmic membrane of muscle fiber, and are stimulated by growth factors released by leucocytes and damaged muscle fibers themselves. In the process of muscular hypertrophy, the increase and maintenance of the cytoplasmic proteic content of adult fibers should be dependent on the addition of new nuclei (nuclei domain theory). The type 2 fibers seem to be more susceptible to these trophic changes in resistance training. In the process of hyperplasia there is an important relationship between the development of cellular lesion and regeneration. Two morphological cell types can be identified, and classified as "new fibers": branches of original cells, occasionally presenting central nuclei, and groups of small fibers in the interstice, with peripheral nuclei. The peculiar histological appearance of muscle cells allows, in the process of degeneration, that only the damaged region of the fiber is remodeled. This condition depends on the migration and incorporation of satellite cells to the damaged region, even if the total resolution of the process is dependent on the extension of the lesion, and the integrity of the basal lamina of muscle fiber. In general, total resolution of the process occurs between 7 and 21 days. In this review paper, the main mechanisms involved in these processes and the inductor factors which can subsidize concepts o the physiotherapeutic practice are discussed.