Satellite cell ablation attenuates short-term fast-to-slow fibre type transformations in rat fast-twitch skeletal muscle

The purpose of this time-course study was to determine whether satellite cell ablation within rat tibialis anterior (TA) muscles exposed to short-term chronic low-frequency stimulation (CLFS) would limit fast-to-slow fibre type transformations. Satellite cells of the left TA were ablated by exposure to γ-irradiation before 1, 2, 5 or 10 days of CLFS and 1 week later where required. Control groups received only CLFS or a sham operation. Continuous infusion of 5-bromo-2′-deoxyuridine revealed that CLFS first induced an increase in satellite cell proliferation at 1 day, up to a maximum at 10 days over control (mean ± SEM, 5.7 ± 0.7 and 20.4 ± 1.0 versus 1.5 ± 0.2 mm⁻², respectively, P < 0.007) that was abolished by γ-irradiation. Myosin heavy chain mRNA, immunohistochemical and sodium dodecyl sulfate polyacrylamide gel electrophoresis analyses revealed CLFS-induced fast-to-slow fibre type transformation began at 5 days and continued at 10 days; in those muscles that were also exposed to γ-irradiation, attenuation occurred within the fast fibre population, and the final fast-twitch to slow-twitch adaptation did not occur. These findings indicate satellite cells play active and obligatory roles early on in the time course during skeletal muscle fibre type adaptations to CLFS.