Title

 

Authors

G.M. Camerino ⁽¹⁾, J-F. Desaphy ⁽¹⁾, S. Pierno ⁽¹⁾, D. Tricarico ⁽¹⁾, A. Scaramuzzi ⁽¹⁾, R. Betto ⁽²⁾, S. Schiaffino ⁽³⁾, D. Conte Camerino ⁽¹⁾.
 
¹Dept. of Pharmacobiology, Faculty of Pharmacy, University of Bari, Italy
²Institute of Neuroscience (C.N.R) Padova,Italy
³Venetian Institute of Molecular Medicine (VIMM), Padova, Italy
 

 

Abstract

Muscle disuse produced by bed rest or spaceflight induces severe atrophy and a slow to fast phenotype transition in muscles functionally devoted to postural maintenance, such as soleus muscle. In previous works we used the hindlimb-unloaded (HU) rodent, a widely accepted model for muscle disuse (Morey-Holton et 2005), at the aim to study the effects of disuse on skeletal muscle ion channels. We have previously demonstrated that simulated microgravity induced increased expression of chloride channels 1 (Clcn1 gene) together with a functional modification of resting chloride conductance in rat and mouse HU soleus muscle, in accord with the phenotypic transition (Desaphy et al 2010). Similarly the expression of skeletal muscle sodium channel (Nav1.4) α subunit (Scn4a gene) was increased in rat soleus muscle after 1 week of HU. The β subunit (Scn1b gene) of sodium channels was unchanged after 1 week and increased after 3 weeks of HU (Desaphy et al 2001). Moreover the activity or gene expression of calcium-activated K⁺ channels (BK) (Kcnma1 gene) (Tricarico et al 2005) decreased in soleus muscle of HU rats, still in accord with change in phenotype. In HU rats, the subunits Kir6.2 (Kcnj11 gene), SUR2a and SUR2b genes (different spliced of the same genes, Abcc9 gene) of ATP-sensitive K⁺ channels (KATP) were down-regulated in parallel to atrophy (Tricarico et al 2010). The Italian Space Agency (ASI) recently sponsored an initiative aimed at investigating the effects of actual microgravity on musculoskeletal apparatus. The mouse drawer system (MDS) was developed by Thales-Alenia-Italia to house mice on board the Shuttle and the International Space Station (ISS) for 92-days. The MDS represents the first European automated rodent spaceflight payload compatible with both Shuttle and ISS. In this context, ASI has promoted a tissue sharing program involving also skeletal muscle atrophy expert investigators. Hindlimb skeletal muscles of spaceflown MDS mice were collected soon after landing in Cape Canaveral and processed for gene expression analysis. Specific real time PCR Taqman-MGB probes were designed to measure expression of various muscle ion channel subunits. The results indicate that the expression of Clcn1, Scn4a and Kcnma1 are changed in the soleus after actual microgravity exposure in the same direction as in the HU model. In contrast to the HU rat, the gene expression of the various subunits of KATP channels was increased in the soleus of MDS mice, in accord with the phenotype transition. In contrast to soleus muscle, the properties of fast-twitch extensor digitorum longus muscle (EDL), including ion channel expression/function, are not affected by HU. Quite surprisingly,  actual microgravity altered ion channel expression in the EDL muscle, suggesting that this muscle may become faster in condition of overall microgravity.
In addition, the protein expression and activity of various Ca²⁺-dependent protein kinase C (PKC) isoforms, which are modulators of ion channel function/expression, was decreased in soleus of HU rats (Pierno et al 2007). In contrast, differently to the HU model, the gene expression of PKCα , PKCδ, and PKCθ, was upregulated in soleus of MDS mice. Further investigation is needed to explain such a discrepancy.
Overall, the results presented here establish a picture of the effects of real microgravity on various ion channels, which may represent druggable targets for countermeasures against disuse-induced muscle wasting.
 
Morey-Holton et al (2005) Adv Space Biol Med. 10:7-40.
Desaphy et al (2010) Pharmacol Res.61(6):553-63.
Desaphy et al (2001) Brain 124:1100-1113.
Tricarico et al (2005) Neurobiol Dis.  2:296-302.
Tricarico et al (2010) J. Physiol 588.5:773-784.
Pierno et al (2007) J Physiol. 584(Pt 3):983-95.