Na v1.4 and Na v1.5 are modulated differently during muscle immobilization and contractile phenotype conversion.

Fabrice Rannou (1) , Jean-Pierre Pennec (1) , Julie Morel , Gildas Guéret (2) , Raphaël Leschiera , Mickael Droguet (1) , Maxime Gioux , Marie-Agnès Giroux-Metges (3)

1 MUST
2 CCTV - Brest - Service de chirurgie thoracique et cardio vasculaire [Brest]
3 M2S - Laboratoire Mouvement Sport Santé

Muscle immobilization leads to modification in its fast/slow contractile phenotype. Since the properties of voltage-gated sodium channels (Na(v)) are different between "fast" and "slow" muscles, we studied the effects of immobilization on the contractile properties and the Na(v) of rat peroneus longus (PL). The distal tendon of PL was cut and fixed to the adjacent bone at neutral muscle length. After 4 or 8 wk of immobilization, the contractile and the Na(v) properties were studied and compared with muscles from control animals (Student's t-test). After 4 wk of immobilization, PL showed a faster phenotype with a rightward shift of the force-frequency curve and a decrease in both the Burke's index of fatigability and the tetanus-to-twitch ratio. These parameters showed opposite changes between 4 and 8 wk of immobilization. The maximal sodium current in 4-wk immobilized fibers was higher compared with that of control fibers (11.5 ± 1.2 vs. 7.8 ± 0.8 nA, P = 0.008), with partial recovery to the control values in 8-wk immobilized fibers (8.6 ± 0.7 nA, P = 0.48). In the presence of tetrodotoxin, the maximal residual sodium current decreased continuously throughout immobilization. Using the Western blot analysis, Na(v)1.4 expression showed a transient increase in 4-wk muscle, whereas Na(v)1.5 expression decreased during immobilization. Our results indicate that a muscle immobilized at optimal functional length with the preservation of neural inputs exhibits a transient fast phenotype conversion. Na(v)1.4 expression and current are related to the contractile phenotype variation.

Keywords: Adenosine Triphosphatases; metabolism; Algorithms; Animals; Electric Stimulation; Electrophysiological Phenomena; Female; Immobilization; Motor Neurons; physiology; Muscle Contraction; drug effects/physiology; Muscle Fatigue; Muscle Fibers; Fast-Twitch; Skeletal; Slow-Twitch; Muscle Proteins; biosynthesis/drug effects/genetics/metabolism; Muscle; drug effects/metabolism; Organ Size; Patch-Clamp Techniques; Phenotype; Rats; Wistar; Reverse Transcriptase Polymerase Chain Reaction; Sodium Channel Blockers; pharmacology; Sodium Channels; biosynthesis/drug effects/metabolism; Tetrodotoxin

Domains: Life Sciences [q-bio]

Fabrice Rannou, Jean-Pierre Pennec, Julie Morel, Gildas Guéret, Raphaël Leschiera, et al.. Na v1.4 and Na v1.5 are modulated differently during muscle immobilization and contractile phenotype conversion.. Journal of Applied Physiology, 2011, 111 (2), pp.495--507. ⟨10.1152/japplphysiol.01136.2010⟩. ⟨hal-01159465⟩