Satellite cell (SC) sterilization attenuates short‐term chronic low‐frequency stimulation (CLFS)‐induced fast‐to‐slow fibre type transitions (F‐S) in rat fast twitch skeletal muscle

Abstract

Our previous study showed long-term CLFS-induced F-S were moderately attenuated in the absence of a viable SC population. Maximum SC activity is seen by 10 days of CLFS. We tested the hypothesis that F-S would be attenuated in the absence of a viable SC population during short-term CLFS. SC’s of the left tibialis anterior were sterilized by exposure to irradiation (25 Gy) before 1, 2, 5, and 10 days of CLFS (1d IRR-Stim, 2d IRR-Stim, 5d IRR-Stim, 10d IRR-Stim; n=6) and 1 week later (10d IRR-Stim). Right legs were controls (C). Groups receiving only CLFS (1d Stim, 2d Stim, 5d Stim, 10d Stim; n=6) were also studied. Sections were analyzed immunohistochemically. Continuous infusion of BrdU revealed that 1, 2, 5, and 10 days of CLFS induced 2.0, 4.8, 8.2, and 5.1 fold increases in SC proliferation over C (P<0.002), respectively, that was abolished in IRR-Stim. F-S differences between IRR-Stim and Stim began at 5 days where IID/X to IIA transitions were delayed in 5d IRR-Stim shown by more IID/X (X±SE: 18.4 ± 2.5 vs 13.9 ± 1.1%; P<0.03) and less IIA/D(X) (1.5 ± 0.9 vs 4.3 ± 1.9; P<0.002) compared with 5d Stim. 10d IRR-Stim had more hybrid fibres delayed in transition from IID/X to I (9.7 ± 2.4 vs 3.1 ± 1.0; P<0.03) resulting in a lower proportion of I fibres (4.5 ± 1.2 vs 7.1 ± 1.5; P<0.03) compared with 10d Stim. We conclude that F-S were moderately attenuated in the absence of a viable SC population during short-term CLFS. NSERC & AHFMR