Effects of chronic administration of clenbuterol on contractile properties and calcium homeostasis in rat extensor digitorum longus muscle.

Laszlo Csernoch,Pascal Sirvent,Robin Candau,Christelle Ramonatxo,Guillaume Py,Olivier Galbes,Aymerick Douillard,Alain Lacampagne

doi:10.1371/journal.pone.0100281

Laszlo Csernoch, Pascal Sirvent + Show 6 more

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https://doi.org/10.1371/journal.pone.0100281

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Abstract

Clenbuterol, a β2-agonist, induces skeletal muscle hypertrophy and a shift from slow-oxidative to fast-glycolytic muscle fiber type profile. However, the cellular mechanisms of the effects of chronic clenbuterol administration on skeletal muscle are not completely understood. As the intracellular Ca2+ concentration must be finely regulated in many cellular processes, the aim of this study was to investigate the effects of chronic clenbuterol treatment on force, fatigue, intracellular calcium (Ca2+) homeostasis and Ca2+-dependent proteolysis in fast-twitch skeletal muscles (the extensor digitorum longus, EDL, muscle), as they are more sensitive to clenbuterol-induced hypertrophy. Male Wistar rats were chronically treated with 4 mg.kg−1 clenbuterol or saline vehicle (controls) for 21 days. Confocal microscopy was used to evaluate sarcoplasmic reticulum Ca2+ load, Ca2+ -transient amplitude and Ca2+ spark properties. EDL muscles from clenbuterol-treated animals displayed hypertrophy, a shift from slow to fast fiber type profile and increased absolute force, while the relative force remained unchanged and resistance to fatigue decreased compared to control muscles from rats treated with saline vehicle. Compared to control animals, clenbuterol treatment decreased Ca2+-transient amplitude, Ca2+ spark amplitude and frequency and the sarcoplasmic reticulum Ca2+ load was markedly reduced. Conversely, calpain activity was increased by clenbuterol chronic treatment. These results indicate that chronic treatment with clenbuterol impairs Ca2+ homeostasis and this could contribute to the remodeling and functional impairment of fast-twitch skeletal muscle.

Highlights

Clenbuterol is a b2-selective adrenergic receptor agonist primarily used for treating asthma
As the intracellular Ca2+ concentration must be finely regulated in many cellular processes, the aim of this study was to investigate the effects of chronic clenbuterol treatment on force, fatigue, intracellular calcium (Ca2+) homeostasis and Ca2+-dependent proteolysis in fast-twitch skeletal muscles, as they are more sensitive to clenbuterol-induced hypertrophy
Muscle morphometric and phenotypic changes following chronic treatment with clenbuterol To investigate the effect on muscle Ca2+ homeostasis of chronic clenbuterol treatment, 22 male Wistar rats received clenbuterol (CBL) or saline vehicle (CTL) for 21 days and the EDL muscles were harvested for morphological and functional investigations

Summary

Introduction

Clenbuterol is a b2-selective adrenergic receptor agonist primarily used for treating asthma. Many studies have focused on the potential use of clenbuterol and some other b–adrenoceptor agonists to counteract muscle wasting associated with many pathological conditions [3]. It is well documented that administration of b–adrenoceptor agonists, such as clenbuterol, results in a dramatic shift from a slow-oxidative to fast-glycolytic muscle fiber type profile [6,7,8]. This change in muscle fiber composition increases muscle fatigue, as reported after chronic administration of b–adrenoceptor agonists [9]

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