Properties of extensor digitorum longus muscle and skinned fibers from adult and aged male and female ACTN3 knockout mice

Abstract

Absence of α-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 caffeineinduced 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 Ca 2+ more slowly than that of wild-types (WT..