Contractile responses in rat extensor digitorum longus muscles at different times of postnatal development |
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Authors: | Y. Péréon J. P. Louboutin J. Noireaud |
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Affiliation: | (1) Laboratory of General Physiology, URA 1340, National Veterinary School, University of Nantes, CP 3013, F-44087 Nantes Cedex 03, France |
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Abstract: | Some contractile properties of small bundles (100–200 m diameter) of muscle fibres isolated from the extensor digitorum longus muscle of rats at different times of development were compared. An increase of resting potential was observed in these muscles from-26.9 mV at 1 day of age to-72.6 mV at 3 months. Twitch tension and duration of postnatal muscles 1–7 days were diminished by reducing [Ca]o (substituted by Mg2+) or adding inorganic cations (Ni2+, Cd2+, La3+), unlike in the oldest animals (14 days–3 months postnatal) where twitch responses were unaffected. In the latter, potentiation of the twitch tension was even recorded in the presence of Ni2+ (0.5–1 mmol·l-1) and Cd2+ (0.5–2 mmol·l-1). Properties of activation and inactivation of the developed tension following elevation of [K]o to 15–200 mmol·l-1 were analysed at the same stages of postnatal development. In contrast to the tension-membrane potential curves for activation, which presented an average negative shift of-17.6 mV between 1 day postnatal and 3 months of age, a voltage dependence of inactivation similar to that encountered in adult extensor digitorum longus muscles, was already reached at 7 days of age. These results suggest an asynchronism in the maturation of the potential-dependent characteristics of the depolarization-contraction coupling mechanism. Furthermore, during the first week postnatal, in relation with poorly developed membrane systems and low [Ca]i-recycling capability, [Ca]o plays a fundamental role in maintaining contraction by replenishing the intracellular calcium pool.Abbreviations ATPase adenosine triphosphatase - [Ca]o ([K]o) extracellular calcium (potassium) concentration - DC depolarization-contraction - EC excitation-contraction - e.d.l. muscle extensor digitorum longus muscle - Em membrane potential - Er resting potential - HEPES N-2 hydroxyethylpiperazine-N-2 ethanesulphonic acid - Ifast fast calcium current - sr sarcoplasmic reticulum - T-tubules transverse tubules |
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Keywords: | Depolarization-contraction coupling Extracellular calcium Development Mammalian skeletal muscle |
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