Slowing of Contractile Properties in Quail Skeletal Muscle With Aging

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Abstract
The effect of aging on muscle contractile function was examined in the anterior latissimus dorsi (ALD) muscle of Japanese quails aged 8 weeks (young adults), 26 weeks, 60 weeks, or 90 weeks (old birds). In vitro contractile measures of the ALD were made at 25 °C (stimulus pulse = 0.1 ms). Twitch contraction time in 90-week-old muscles was significantly greater than 8 to 26-week-old muscles (150 ± 8 ms vs 168 ± 18 ms). Similarly, one-half relaxation time of the twitch was increased in the ALD from old birds (221 ±17 ms) relative to adult birds 8–26 weeks (173 ± 11). Aging produced a greater fusing of twitches at stimulation frequencies of 5 and 10 Hz, and this resulted in a leftward shift of the force-frequency curve at these frequencies. Shortening velocity measured by the force-velocity method (Vmax) decreased from 2.6 ± 0.2 muscle lengthls (mLls) to 1.19 ± 0.02 mLls in 8 and 90-week-old muscles, respectively. Maximal velocity of unloaded shortening as measured by the slack test decreased from 3.6 ± 0.7 mLls to 2.4 mLls in 8-week-old and 90-week-old muscles, respectively. Maximal tetanic force (60.6 ±3.1 mN) and specific force (11.3 ± 0.3 Nlcm2) were similar in young adult and old muscles. These data indicate that aging induces a slowing of both twitch contractile characteristics and shortening velocity in the ALD, without affecting maximal force capabilities.

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