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First published online July 2, 2004
Journal of Experimental Biology 207, 2793-2802 (2004)
Published by The Company of Biologists 2004
doi: 10.1242/jeb.01076

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

Cyril Bozzo^1,*, Laurence Stevens¹, Valentine Bouet², Valérie Montel¹, Florence Picquet¹, Maurice Falempin¹, Michel Lacour² and Yvonne Mounier¹

¹ Laboratoire de Plasticité Neuromusculaire, UPRES EA 1032, IFR 118, Bâtiment SN4, Université des Sciences et Technologies de Lille, 59655 Villeneuve d'Ascq cedex, France
² Laboratoire de Neurobiologie des Restaurations Fonctionnelles, CNRS Unité Mixte de Recherche 6562, Université de Provence, 52, Faculté de St Jérôme, 13397 Marseille cedex 20, France

^* Author for correspondence (e-mail: cyelboz{at}hotmail.com)

Accepted 7 May 2004

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.

Key words: 2G-centrifugation, skinned fiber, rat, soleus, plantaris, contractile and regulatory protein, electrophoresis, RT-PCR