Contractile properties of rat soleus muscle after 15 days of hindlimb suspension

Abstract

The properties of the contractile elements interacting to develop force in atrophied rat soleus muscle were studied by using single skinned fibers, which permitted direct access to the contractile apparatus. Muscle atrophy was induced by 15 days of hindlimb suspension. Suspension resulted in a decrease of maximal tension relative to an important decline in fiber diameter. Ca affinity of the contractile proteins was not changed insofar as the tension-pCa relationship was not shifted along the pCa axis. However, after hindlimb suspension 1) the value of the Hill coefficient from the tension-pCa curve was found to be higher, 2) a higher Ca threshold for activation was reported, and 3) a significant increase in contraction kinetics was described. All these results suggested that after suspension the mechanical properties of the slow-twitch soleus appeared to resemble more closely those of a fast-twitch muscle. Our results were in complete agreement with published histochemical data.

Novel murine clonal cell lines either express slow or mixed (fast and slow) muscle markers following differentiation in vitro

“…Muscle inactivity results in a transition from slow-oxidative toward a fast-glycolytic phenotype (Bigard et al, 1998;Hourde et al, 2005;Stevens et al, 1990), that affects both MHC and enzymes involved in metabolism. Conversely, controlled stimulation of a rapid-glycolytic muscle induces changes toward a slow-oxidative phenotype (Pette and Vrbova, 1985).…”

Identification of O-linked N-Acetylglucosamine Proteins in Rat Skeletal Muscle Using Two-dimensional Gel Electrophoresis and Mass Spectrometry

“…These transitions were associated with aerobic-oxidative to glycolytic metabolic changes (32) that involved both variations in the glucose metabolism and phosphorylation/dephosphorylation events (33,34). Moreover, HU applied for 14 days on the slow-twitch antigravitational soleus caused an atrophy and a decrease in calcium sensitivity of skinned fibers (35). As previously mentioned, UDP-GlcNAc has been demonstrated to be sensitive to glucose levels; moreover, correlations between the glycogen content and the O-GlcNAc level have been measured in skeletal muscle (36).…”

Age-dependent effects of treadmill exercise during a period of inactivity

“…If atrophy is the primary underlying mechanism to explain hindlimb unweighted induced decline in force generating capacity, there would be no change in specific tension. In previous studies specific tension is reduced suggesting that atrophy is only a part of the explanation for unweighting induced reduction in force (Alley and Thompson, 1997;Fitts et al, 2001;Sandmann et al, 1998;Stevens et al, 1990). In the current study, there is also a significant decrease in specific tension with hindlimb unweighting in the young and very old as the diameter and force do not decrease proportionately.…”

“…The increased ATPase activity was attributed to the non-weight bearing-induced increase in the SERCA1 (fast) isoform expression in the soleus (Peters et al, 1999;Schulte et al, 1993). After 15 days of hindlimb unweighting Stevens et al, (1990) also showed increased calcium uptake and release by the SR in the soleus muscle that functionally were comparable to fast muscle. Calcium release from the SR is regulated by the voltagesensitive dihydropuridine receptor, which triggers the release of SR calcium by the ryanodine receptors.…”

“…Thus, the decrease in diameter in the very old partly explains the decrease in force generating capacity. The other mechanisms suggested for the altered specific tension following unweighting include a decrease in the total number of actomyosin cross bridges, alterations in the structure of myosin and/or a preferential loss of actin (Stevens et al, 1990;Thomason et al, 1989;Zhong et al, 2006). These underlying cellular mechanisms need to be investigated further.…”