Metabolic and morphologic properties of single muscle fibers in the rat after spaceflight, Cosmos 1887

Abstract

The adaptation of a slow (soleus, Sol) and a fast (medial gastrocnemius, MG) skeletal muscle to spaceflight was studied in five young male rats. The flight period was 12.5 days and the rats were killed approximately 48 h after returning to 1 g. Five other rats that were housed in cages similar to those used by the flight rats were maintained at 1 g for the same period of time to serve as ground-based controls. Fibers were classified as dark or light staining for myosin adenosine triphosphatase (ATPase). On the average, the fibers in the Sol of the flight rats atrophied twice as much as those in the MG. Further, the fibers located in the deep (close to the bone and having the highest percentage of light ATPase and high oxidative fibers in the muscle cross section) region of the MG atrophied more than the fibers located in the superficial (away from the bone and having the lowest percentage of light ATPase and high oxidative fibers in the muscle cross-section) region of the muscle. Based on quantitative histochemical assays of single muscle fibers, succinate dehydrogenase (SDH) activity per unit volume was unchanged in fibers of the Sol and MG. However, in the Sol, but not the MG, the total amount of SDH activity in a 10-microns-thick section of a fiber decreased significantly in response to spaceflight. Based on population distributions, it appears that the alpha-glycerophosphate dehydrogenase (GPD) activities were elevated in the dark ATPase fibers in the Sol, whereas the light fibers in the Sol and both fiber types in the MG did not appear to change. The ratio of GPD to SDH activities increased in the dark (but not light) fibers of the Sol and was unaffected in the MG. Immunohistochemical analyses indicate that approximately 40% of the fibers in the Sol of flight rats expressed a fast myosin heavy chain compared with 22% in control rats. Further, 31% of the fibers in the Sol of flight rats expressed both fast and slow myosin heavy chains compared with 8% in control rats. Immunohistochemical changes in the MG were minimal. These data suggest that the magnitude and direction of enzymatic activity and cell volume changes are dependent on the muscle, the region of the muscle, and the type of myosin expressed in the fibers. Further, the ability of fibers to maintain normal or even elevated activities per unit volume of some metabolic enzymes is remarkable considering the marked and rapid decrease in fiber volume.

Skeletal Muscle Adaptations with Age, Inactivity, and Therapeutic Exercise

“…42,59 Using immunocytochemistry to determine fiber type, the percentage of soleus fibers showing a positive reaction with both slow and fast MHC antibodies increased from 0 to 16% following 14 days of inactivity, whereas those reacting only to slow MHC antibodies declined from 90 to 76%. 63 Thus inactivity increases the number of fibers coexpressing two myosin isoforms in antigravity slow muscles by inducing fast myosin expression in slow fibers.…”

Role(s) of Mechanical Load and Satellite Cells in The Regulation of The Size of Soleus Muscle Fiber in Rats

“…Atrophy of soleus muscle fibers in response to gravitational unloading by actual spaceflight (Allen et al, 1996;Martin et al, 1988;Miu et al, 1990;Oganov and Potapov, 1976;Ohira et al, 1992;Tischler et al, 1993) or hindlimb suspension (Ohira et al, 1992;Talmadge et al, 1996;Tischler et al, 1993;Winiarski et al, 1987) has been reported in the previous studies. Wang et al (2006) reported fiber atrophy in soleus muscle of Wistar Hannover rats following 16 days of hindlimb unloading (Fig.…”

“…On the other hand, fiber atrophy is induced during the periods of decreased neuromuscular activity, e.g., in response to gravitational unloading by actual spaceflight (Allen et al, 1996;Martin et al, 1988;Miu et al, 1990;Oganov and Potapov, 1976;Ohira et al, 1992), or simulation models such as hindlimb suspension of rats (Ohira et al, 1992;Talmadge et al, 1996;Tischler et al, 1993;Winiarski et al, 1987) and/or human bedrest (Ohira et al, 1999). Such atrophy is prominent in antigravity muscles, such as soleus, composed of mainly slow-twitch fibers (Goldspink et al, 1986;Ohira et al, 1987 and1992) and with a marked reduction in fiber length and tension development due to plantarflexion of ankle joints during gravitational unloading Ohira et al, 2002).…”

“…Such atrophy is prominent in antigravity muscles, such as soleus, composed of mainly slow-twitch fibers (Goldspink et al, 1986;Ohira et al, 1987 and1992) and with a marked reduction in fiber length and tension development due to plantarflexion of ankle joints during gravitational unloading Ohira et al, 2002). Unloading-related atrophy is generally associated with the shift of fiber phenotype from slow-to fast-twitch type (Allen et al, 1996;Martin et al, 1988;Miu et al, 1990;Oganov and Potapov, 1976;Ohira et al, 1992;Winiarski et al, 1987).…”

Analysis by two-dimensional Blue Native/SDS-PAGE of membrane protein alterations in rat soleus muscle after hindlimb unloading

“…In skeletal muscle, this large complex of membraneassociated proteins links the sub-sarcolemmal actin cytoskeleton to the extracellular matrix and is thought to provide protection from stresses imposed during muscle contraction (Petrof et al 1993). The increased expression of -DG and -syn in HU muscles parallels the slow-to-fast twitch conversion of soleus Wbers: this phenomenon involves a reduction in slow-type I MHC isoform and an increase in fast IIA MHC, in which soleus muscle gains some fast-twitch mechanical features (Miu et al 1990) but does not increase the force generation. Consequently, the increase in DGC follows the conversion of slow-to-fast twitch Wbers even though there is not a strong increase in contractile activities, and this is probably a reactive mechanism for protecting muscle Wbers.…”