INCREASE IN RAT SOLEUS MYOTENDINOUS INTERFACE AFTER A 14-D SPACEFLIGHT

Myotendinous junctions (MTJs) transmit contractile force from skeletal muscles to tendons. The effects of a 14-d spaceflight on MTJ were stu died in the soleus muscle of male adult Sprague Dawley rats by transmi ssion electron microscopy and histomorphometric techniques. We showed that the length of the junctional membrane relative to the muscle fibe r diameter increased by 58 % after 14 d of spaceflight. This increase accompanies morphological changes at MTJs. The flight MTJs appeared mo re shredded. The ends of the muscle fibers exhibited T tubule dilatati on, swollen mitochondrial Z-disk streaming, loss of myofilaments, a th inning down of subplasmalemmal densities, multivesicular bodies and si gns of junctional membrane and basal lamina remodelling. The ultrastru ctural observations suggest that the increase in myotendinous interfac e could result from the extracellular matrix spreading into remodellin g muscle fiber, whereas the constraints related to unloading were redu ced by spaceflight conditions. ((C) Academie des sciences / Elsevier, Paris.).