Mechanical load-dependent regulation of satellite cell and fiber size in rat soleus muscle

Abstract

The effects of mechanical unloading and reloading on the properties of rat soleus muscle fibers were investigated in male Wistar Hannover rats. Satellite cells in the fibers of control rats were distributed evenly throughout the fiber length. After 16 days of hindlimb unloading, the number of satellite cells in the central, but not the proximal or distal, region of the fiber was decreased. The number of satellite cells in the central region gradually increased during the 16-day period of reloading. The mean sarcomere length in the central region of the fibers was passively shortened during unloading due to the plantarflexed position at the ankle joint: sarcomere length was maintained at <2.1 microm, which is a critical length for tension development. Myonuclear number and domain size, fiber cross-sectional area, and the total number of mitotically active and quiescent satellite cells of whole muscle fibers were lower than control fibers after 16 days of unloading. These values then returned to control values after 16 days of reloading. These results suggest that satellite cells play an important role in the regulation of muscle fiber properties. The data also indicate that the satellite cell-related regulation of muscle fiber properties is dependent on the level of mechanical loading, which, in turn, is influenced by the mean sarcomere length. However, it is still unclear why the region-specific responses, which were obvious in satellite cells, were not induced in myonuclear number and fiber cross-sectional area.

The Non-Thermal Effects of Pulsed Ultrasound Irradiation on the Development of Disuse Muscle Atrophy in Rat Gastrocnemius Muscle

“…There is no report that ultrasound 8 irradiation decrease tissue temperature. The decrease in the muscle 9 temperature was not influenced by US irradiation, because the temperature 10 decrease was also observed in the sham US group. The possibility of anesthetic 11 influence is low, because core temperature was not changed in both the sham 12 US and US groups.…”

“…Core and muscle temperatures 13 The time course changes in core and muscular temperatures before and 14 during ultrasound irradiation were measured in the pilot study (Fig.1). In the 15 US group, the average core and muscle temperature at 5 min before US Muscle fiber diameter 7 The development of muscle atrophy was confirmed in the Im, sham US, and 8 US groups, whereas muscle fiber necrosis and regenerating fibers were not 9 observed in the muscles of all groups in the sections stained with H&E (data not 10 shown). Representative photographs of cross-sections stained for myosin 11 ATPase activity (pH 4.3) in the gastrocnemius muscle are shown in Fig.…”

“…US may 9 be administered in either a continuous or a pulsed mode (Rutjes et al 2010). 10 Pulsed US produces non-thermal effects and is used to aid in the reduction of ribosome, which increases the muscle fiber volume (Goldspink 1999). In 3 addition, mechanical stimulation loading is known to increase vascular 4 endothelial growth factor (VEGF) and basic fibroblast growth factor (bFGF), 5 which results in the development of more skeletal muscle capillaries (Folkman 6 et al 1988).…”

“…Committee for Animal Experimentation at Nagasaki University. We obtained 10 62, eight-wk-old, male Wistar rats (220 ± 10 g) from Kudo Laboratories (Tokyo, 11 Japan). The animals were housed in cages inside a room with a 12-h dark/light 12 cycle.…”

“…An aqueous gel (Aquasonic 100, 16 gastrocnemius muscle in the US group was irradiated through the shaved skin 1 for 15 min at a frequency of 1 MHz and an intensity of 1.0 W/cm 2 . 2 The US irradiation at the above frequency and intensity should extend to rat Immunohistochemical analysis of and BrdU-positive muscle nuclei 10 New muscle nuclei that were traced to satellite cells were identified by using 11 double immunostaining with anti-BrdU and anti-dystrophin antibodies. Muscle 12 nuclei are always located inside of the sarcolemma, which is labeled by 13 anti-dystrophin antibody, and new nuclei incorporate BrdU in their DNA.…”