...

Scientific Programme

Physiology & Nutrition

CP-PN08 - Physiology (mixed)

Date: 05.07.2024, Time: 11:00 - 12:00, Lecture room: M2+M3

Description

Chair TBA

Chair

TBA
TBA
TBA

ECSS Paris 2023: CP-PN08

Speaker A Yung-Li HUNG

Speaker A

Yung-Li HUNG
Juntendo University, Graduate School of Health and Sports Science
Japan
"The effects of endurance training and cast immobilization on muscle satellite cell number and proliferation in vitro in old female rats"

INTRODUCTION: Skeletal muscles undergoe rapid and profound atrophy in response to inactivity such as limb immobilization and bed rest. In mature or old rats, muscle atrophy also occurs mainly through loss of the existing mass, including a reduction in the loss of myonuclei. It is likely that muscle satellite cells play an essential role in preventing age-related or inactive muscle atrophy, because skeletal muscle fibers are terminally differentiated (postmitotic) and require the proliferation of muscle satellite cells to provide new myonuclei for maintaining skeletal muscle. Endurance training increases the muscle satellite cell pool of skeletal muscles (1), but the effect of endurance training on muscle satellite cell proliferation is unclear. There is no information on how the proliferative function of muscle satellite cells is affected by endurance training and inactivity. This study aimed to examine the effects of endurance training and cast immobilization on the proliferative function of muscle satellite cells in vitro. METHODS: Female F344 rats (20 months old) were divided into three experimental groups: control (CON), endurance training (T), and immobilization (IM) groups. Rats in the T group were trained 5 days per week on a treadmill for 10 weeks, and rats in the IM group were subjected to cast immobilization of both lower extremities using casting tape for 10 days. After exercise training or cast immobilization, primary satellite cells were isolated from the quadriceps and gastrocnemius muscles of the rats. The effects of exercise training or cast immobilization on isolated satellite cell proliferation were examined by BrdU immunostaining. RESULTS: The number of isolated satellite cells was significantly higher in the T group than that in the CON group. On the other hand, the satellite cell number was reduced in the IM group compared to that in the CON group. The BrdU-positive cell ratio was significantly lower in the IM group than in the CON and T groups, but was not significantly different between the CON and T groups. CONCLUSION: These results suggest that inactivity in old female rats may reduce the proliferative function of muscle satellite cells and that exercise training increases the number of muscle satellite cells. (1) M Kurosaka 1, H Naito, Y Ogura, S Machida, S Katamoto. Acta Physiol (Oxf). (2012); 205(1):159-66.

Read CV Yung-Li HUNG

ECSS Paris 2023: CP-PN08

Speaker B Tatsuhiro Yamaguchi

Speaker B

Tatsuhiro Yamaguchi
The University of Tokyo, Graduate School of Arts and Sciences
Japan
"Muscle disuse leads to neuromuscular transmission impairment and atrophy of fast-twitch myofibers via neuromuscular junction degeneration in mice"

INTRODUCTION: Physical inactivity leads to a more pronounced decline in muscle strength than in muscle mass. Several studies suggest that the structural degeneration of neuromuscular junction (NMJ) due to muscle disuse is one of the contributing factors to this phenomenon, but direct evidence has yet to be established. We aimed to elucidate the influence of disuse-induced NMJ degeneration on neuromuscular function by using two disuse models in mice with different levels of neuromuscular activity. METHODS: Male C57BL/6J mice (12-13 weeks old) were divided into control (CON), immobilization (IM), and immobilization with suspension (IMS) groups. IM mice were subjected to cast immobilization of lower hindlimbs but were allowed free movement. IMS mice were subjected to the same hindlimb immobilization as IM mice, and were then suspended to severely restrict their neuromuscular activity. After 20 days of intervention, plantar flexion torque and compound muscle action potential (CMAP) evoked by repetitive sciatic nerve stimulation were measured. The ratio of 10th to 1st CMAP amplitude was used as an index of neuromuscular transmission. Subsequently, mice were dissected and the wet weights of the gastrocnemius, plantaris, and soleus muscles were determined. The myofiber cross-sectional area (CSA) and NMJ morphology for each fiber type were evaluated by immunohistochemistry. RESULTS: The wet weight of the gastrocnemius muscle was the highest in CON and the lowest in IMS. The wet weight of the plantaris and soleus muscles was the highest in CON, but was not significantly different between IM and IMS. The tetanic plantar flexion torque evoked by 100- and 200-Hz stimulation was significantly lower in IMS than in CON and IM, even when normalized by the muscle wet weight. CMAP amplitude was significantly smaller in IMS than in CON and IM. The amplitude ratio of 10th to 1st CMAP was significantly lower in IMS than in CON but not significantly different between CON and IM. In both IM and IMS mice, myofiber CSA expressed as a percentage of the mean CSA in CON was significantly lower in type 2b fibers than in type 2a and 2x fibers in the plantaris but was not significantly different between fiber types in the soleus. The proportion of denervated myofibers in the plantaris and soleus muscles was significantly higher in IMS than in CON. The size of presynaptic nerve terminals but not acetylcholine receptors was significantly smaller in IMS than in CON. These differences were more pronounced in fast-twitch fibers than in slow-twitch fibers in the soleus. CONCLUSION: Our results suggest that muscle disuse impairs neuromuscular transmission via degeneration of presynaptic nerve terminals of NMJ. NMJ structure is more severely deteriorated in fast-twitch myofibers, resulting in the preferential atrophy of the fibers. Both impaired neuromuscular transmission and atrophy of fast-twitch fibers lead to a more pronounced decline in muscle strength than in muscle mass during muscle disuse.

Read CV Tatsuhiro Yamaguchi

ECSS Paris 2023: CP-PN08

Speaker C YI CHEN CHEN

Speaker C

YI CHEN CHEN
National Institute of Fitness and Sports in Kanoya, Doctors Course in Physical Education
Japan
"The effects of bone mechanical stress produced by electrical-stimulation–induced muscle contraction force on osteocalcin secretion over time"

INTRODUCTION: It is well known that exercise brings multiple benefits, and osteocalcin (Ocn), a bone-derived hormone, is considered one of the beneficial factors involved in the process. It has been shown to help improve insulin sensitivity, glucose and fat metabolism, and cognitive development. However, for those who are unable to do voluntary exercise, passive exercise triggered by external electrical stimulation (ES) may be a solution. Nevertheless, whether even a relatively small bone strain from ES-induced muscle contraction force can stimulate osteocytes to promote Ocn secretion, and how long any such increase in Ocn secretion lasts, remains unclear. In this study, therefore, we aimed to investigate the effects of ES-induced muscle contraction on Ocn secretion and changes in this relationship over time. METHODS: Sixteen male ten-week-old Fischer 344 rats were randomly assigned to two groups: (1) low-frequency ES at 10 Hz (LF, n = 8); (2) high-frequency ES at 100 Hz (HF, n = 8). An acute 30 min ES intervention was applied specifically to the left tibialis anterior (TA) muscle under isoflurane inhalational anesthesia. We recorded in vivo tibia bone strain caused by ES-induced muscle contraction force at both ES frequencies using a strain gauge. Blood samples were collected from the caudal vein just before, 0, 0.25, 0.5, 1, 3, 5, 7, and 14 days after the ES intervention, and fasting blood glucose (FBG) was measured at the same time. Serum was extracted to analyze the concentration of Ocn at each timepoint using enzyme-linked immunosorbent assay (ELISA). The changes in Ocn and FBG concentration over time and the correlation between them were analyzed. RESULTS: The in vivo tibia bone strain during ES was 35 µε at 10 Hz and 264 µε at 100 Hz. However, there was no significant difference between the groups in Ocn and FBG concentrations at any timepoint. The Ocn concentration in the LF group increased significantly at 0.25, 0.5, 1, 5, and 14 days after the ES intervention. In the HF group, the concentration decreased immediately after the intervention and then increased significantly at 0.25, 0.5, 1, 3, and 14 days after the ES intervention. There were significant decreases in FBG at all timepoints following the ES intervention in both groups. Further, significant negative correlations were observed between Ocn and FBG concentrations, as well as between the changes in Ocn and the changes in FBG. CONCLUSION: Electrical-stimulation–induced muscle contraction force can promote an increase in Ocn secretion for up to five days, as well as a sustained reduction in FBG for two weeks. The elevation in Ocn secretion correlates with lower FBG levels.

Read CV YI CHEN CHEN

ECSS Paris 2023: CP-PN08