Experimental induction of ring fibers in regenerating skeletal muscle.

Light microscopy and electron microscopy were used to study the formation of ring fibers induced experimentally in regenerating muscle subjected to tenotomy-induced tension deficiency. Anterior tibial rat muscles were injured by intramuscular injection of mepivacain, tenotomized at varying stages of the regenerative process, and analyzed 30 days after sectioning the tendon. The combination of regeneration and tenotomy led to the appearance of ring fibers at different developmental stages. Ring fibers were not observed in regenerating control muscles and were scarce in tenotomized controls. Our results showed that the regenerative phase in which tension deficiency was established had a significant influence on the number of developing ring fibers; the number increased when tenotomy was performed during subsarcolemmic myofibrillogenesis in regenerating fibers. As a consequence, one might hypothesize that tension deficiency during muscle fiber repair plays a critical role in ring fiber formation.