Journal
MUSCLE & NERVE
Volume 43, Issue 1, Pages 37-48Publisher
WILEY
DOI: 10.1002/mus.21778
Keywords
alpha-actinin-3; exercise; sarcoplasmic reticulum; skeletal muscle; skinned fiber
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Absence of alpha-actinin-3, encoded by the ACTN3 'speed gene,' is associated with poorer sprinting performance in athletes and a slowing of relaxation in fast-twitch muscles of Actn3 knockout (KO) mice. Our first aim was to investigate, at the individual-fiber level, possible mechanisms for this slowed relaxation. Our second aim was to characterize the contractile properties of whole extensor digitorum longus (EDL) muscles from KO mice by age and gender. We examined caffeine-induced Ca2+ release in mechanically skinned EDL fibers from KO mice, and measured isolated whole EDL contractile properties. The sarcoplasmic reticulum of KO muscle fibers loaded Ca2+ more slowly than that of wild-types (WTs). Whole KO EDL muscles had longer twitch and tetanus relaxation times than WTs, and reduced mass and cross-sectional area. These effects occurred in both male and female mice, but they diminished with age. These changes in KO muscles and fibers help to explain the effects of alpha-actinin-3 deficiency observed in athletes. Muscle Nerve 43: 37-48, 2011
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