Proceedings of The Physiological Society

Europhysiology 2018 (London, UK) (2018) Proc Physiol Soc 41, PCA192

Poster Communications

Preferential skeletal muscle myosin loss is prevented by neuromuscular electrical stimulation in steroid-denervation rats

T. Yamada1, K. Himori1, D. Tatebayashi1, R. Yamada1, Y. Ashida1, T. Imai1, Y. Masuda1, K. Kanzaki3, D. Watanabe4, M. Wada5, H. Westerblad2, L. T. Johanna2

1. Sapporo Medical University, Sapporo, Japan. 2. Karolinsk Institute, Stockholm, Sweden. 3. Kawasaki University of Medical Welfare, Kawasaki, Japan. 4. La Trobe University, Melborune, Victoria, Australia. 5. Hiroshima university, Higashi Hiroshima, Japan.

Steroid has been shown to induce preferential depletion of myosin and severe muscle weakness in denervated skeletal muscle (Rouleau et al, 1987). We here investigated whether neuromuscular electrical stimulation (ES) treatment could prevent these deleterious changes in steroid-denervation (S-D) rat. All experimental procedures were approved by the Committee on Animal Experiments of Sapporo Medical University (No. 16-076). Wistar rats (9 week old, n=24) were assigned into control (CNT) (n=12) and S-D (n=12) group. Under 2% isoflurane anesthesia, S-D was induced by cutting the sciatic nerve and subsequent daily injection of dexamethasone (5 mg/kg) for 7 days. Throughout the ES treatment, rats were anesthetized by isoflurane inhalation and their left foot was secured in a foot plate connected to a torque sensor (S-14154, Takei Scientific Instruments). Plantarflexor muscles were electrically stimulated supramaximally (45 V) using a pair of surface electrodes to produce four sets of five isometric contractions each day. After the experimental periods, rats were killed by cervical dislocation under isoflurane anesthesia and gastrocnemius (GAS) muscle weight, skinned muscle fiber force, and protein and mRNA expression were measured. Data are presented as mean ± SEM. A two-way ANOVA followed by Tukey-Kramer post hoc test was used to examine the statistical significance. ES treatment partly prevented the S-D-induced decreases in plantarflexor in situ maximum isometric torque (CNT: 125 ± 2, CNT+ES: 116 ± 5, S-D: 15 ± 5, S-D+ES: 43 ± 3 mNm [n=5-6]; P < 0.05: S-D vs S-D+ES) and GAS muscle weight (CNT: 1461 ± 43, CNT+ES: 1447 ± 43, S-D: 769 ± 21, S-D+ES: 938 ± 23 mg [n=5-6]; P < 0.05: S-D vs S-D+ES). ES treatment fully prevented S-D-induced decreases in maximum force in skinned fiber (CNT: 264 ± 16, CNT+ES: 275 ± 16, S-D: 134 ± 16, S-D+ES: 258 ± 19 kN/m2 [n=14-18]; P < 0.05: S-D vs S-D+ES) and myosin heavy chain (MyHC) expression ([n=5-6]; S-D vs S-D+ES, P < 0.05), as well as increases in the reactive oxygen/nitrogen species-generating enzymes NADPH oxidase 2 and 4, autolyzed active calpain-1 and mRNA expression of the muscle-specific ubiquitin ligases muscle ring finger-1 (MuRF-1) and atrogin-1 ([n=5-6]; S-D vs S-D+ES, P < 0.05). In conclusion, ES treatment fully prevented the decrease in myofibrillar force production due to decreased MyHC expression and partly prevented muscle atrophy in S-D muscle. The S-D-induced protein degradation involves reactive oxygen species-dependent activation of calpain-1 and the muscle-specific ubiquitin ligases MuRF-1 and atrogin-1.

Where applicable, experiments conform with Society ethical requirements