Hypergravity from conception to adult stage: effects on contractile properties and skeletal muscle phenotype

Abstract

SUMMARY This study examined the effects of an elevation of the gravity factor(hypergravity – 2 g) on the molecular and functional characteristics of rat soleus and plantaris muscles. Long Evans rats were conceived, born and reared (CBR) continuously in hypergravity conditions until the age of 100 days. Whole muscle morphological parameters, Ca2+activation characteristics from single skinned fibers, troponin (Tn) subunit and myosin heavy (MHC) and light (MLC) chains isoform compositions were examined in CBR and control muscles from age-paired terrestrial rats. Decreases in body and muscle mass in soleus and plantaris muscles were observed and associated, in the soleus, with a decrease in fiber diameter. The specific force of CBR soleus fibers was increased, and correlated with the elevation of Ca2+ affinity. This was accompanied by slow-to-slower TnC and TnI isoform transitions and a rearrangement in TnT fast isoform content. The MHC transformations of the soleus after hypergravity were associated with the up (down)-regulation of the MHCI (MHCIIa) mRNA isoforms. The MLC2 phosphorylation state remained unchanged in the soleus muscle. The results suggested that the gravity factor could interact with rat muscle development and that hypergravity experiments could provide good tools for the study of myofibrillar protein plasticity and their associated pathways of regulation.

Ground-Based Researches on the Effects of Altered Gravity on Mice Development

“…Rats born and reared in hypergravity showed changes in the morphological and contractile properties (Picquet et al 2002;Bozzo et al 2004). At the contrary, unloading conditions atrophied skeletal muscles with different degrees according to the muscle type and muscle function (Picquet et al 1998;Fitts et al 2000).…”

“…A possible explanation for this difference was the increased proportion of slow fibres in postural muscles. Previous studies showed that the morphological and contractile properties of postural muscles shifted to a slower type in rats born and reared in hypergravity during 100 days (Picquet et al 2002;Bozzo et al 2004). It can be supposed therefore that the exposition to hypergravity during a shorter time windows of the early motor development sufficed to definitely shift the muscles typology to a slower type, that offers a better resistance to fatigue and could counter balance some deleterious effects related to ageing.…”

“…This transformation can be correlated with a decrease in both calcium sensitivity and affinity of the contractile system and by transitions in the contractile proteins, especially the myosin heavy chain (MHC) isoforms, under neural influence. Rats born and reared in HG showed changes in the morphological and contractile properties with a decrease in absolute muscle weight, an increase in fibre cross-sectional area and in relative maximal tension (Picquet et al 2002;Bozzo et al 2004;Stevens et al 2003). The soleus muscle changed into a slower type, while the plantaris, its fast agonist, showed a faster contractile behaviour, in relation with modifications in MHC and regulatory troponin contents.…”

Hypergravity exposure during gestation modifies the TCRβ repertoire of newborn mice

“…These observations are in agreement with previous data. Indeed, lower birth weights have been reported in hypergravity-raised rats1314. Reduced pup weight could be explained by the higher energy expenditure induced in mothers by the hypergravity environment.…”

Cellular patterns of the atrophic response in murine soleus and gastrocnemius muscles submitted to simulated weightlessness

“…Changes in the composition of these contractile proteins are accepted as one of the phenotypic modifications related to skeletal muscle atrophy (Stevens et al 2000;Bozzo et al 2003). Some authors, using various experimental conditions (Bozzo et al 2003;Bozzo et al 2004;Stevens et al 2004), reported that the alterations in myosin heavy chain (MHC) isoforms are qualitatively similar and correspond with those in MLC isoforms. Our results (Fig.…”