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β2-Adrenergic stimulation enhances Ca2+ release and contractile properties of skeletal muscles, and counteracts exercise-induced reductions in Na+-K+-ATPase Vmax in trained men
Department of Nutrition, Exercise and Sports, Section of Integrated Physiology, University of Copenhagen, Denmark .
Department of Nutrition, Exercise and Sports, Section of Integrated Physiology, University of Copenhagen, Denmark .
Mittuniversitetet, Fakulteten för humanvetenskap, Avdelningen för hälsovetenskap. Department of Sports Science and Biomechanics, University of Southern Denmark, Denmark . (NVC)
Department of Biology, University of Copenhagen, Denmark .
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2014 (engelsk)Inngår i: Journal of Physiology, ISSN 0022-3751, E-ISSN 1469-7793, Vol. 592, nr 24, s. 5445-5459Artikkel i tidsskrift (Fagfellevurdert) Published
Abstract [en]

The aim of the present study was to examine the effect of β2-adrenergic stimulation on skeletal muscle contractile properties, sarcoplasmic reticulum (SR) rates of Ca2+ release and uptake, and Na+-K+-ATPase activity before and after fatiguing exercise in trained men. The study consisted of two experiments (EXP1, n = 10 males, EXP2, n = 20 males), where β2-adrenoceptor agonist (terbutaline) or placebo was randomly administered in double-blinded crossover designs. In EXP1, maximal voluntary isometric contraction (MVC) of m. quadriceps was measured, followed by exercise to fatigue at 120% of maximal oxygen uptake (V˙O2, max ). A muscle biopsy was taken after MVC (non-fatigue) and at time of fatigue. In EXP2, contractile properties of m. quadriceps were measured with electrical stimulations before (non-fatigue) and after two fatiguing 45 s sprints. Non-fatigued MVCs were 6 ± 3 and 6 ± 2% higher (P < 0.05) with terbutaline than placebo in EXP1 and EXP2, respectively. Furthermore, peak twitch force was 11 ± 7% higher (P < 0.01) with terbutaline than placebo at non-fatigue. After sprints, MVC declined (P < 0.05) to the same levels with terbutaline as placebo, whereas peak twitch force was lower (P < 0.05) and half-relaxation time was prolonged (P < 0.05) with terbutaline. Rates of SR Ca2+ release and uptake at 400 nm [Ca2+] were 15 ± 5 and 14 ± 5% (P < 0.05) higher, respectively, with terbutaline than placebo at non-fatigue, but declined (P < 0.05) to similar levels at time of fatigue. Na+-K+-ATPase activity was unaffected by terbutaline compared with placebo at non-fatigue, but terbutaline counteracted exercise-induced reductions in maximum rate of activity (Vmax) at time of fatigue. In conclusion, increased contractile force induced by β2-adrenergic stimulation is associated with enhanced rate of Ca2+ release in humans. While β2-adrenergic stimulation elicits positive inotropic and lusitropic effects on non-fatigued m. quadriceps, these effects are blunted when muscles fatigue.

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2014. Vol. 592, nr 24, s. 5445-5459
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URN: urn:nbn:se:miun:diva-24056DOI: 10.1113/jphysiol.2014.277095ISI: 000346341600011Scopus ID: 2-s2.0-84916612993OAI: oai:DiVA.org:miun-24056DiVA, id: diva2:778100
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CODEN: JPHYA

Tilgjengelig fra: 2015-01-09 Laget: 2015-01-07 Sist oppdatert: 2018-01-11bibliografisk kontrollert

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