SLOWING OF CONTRACTILE PROPERTIES IN QUAIL SKELETAL-MUSCLE WITH AGING

The effect of aging oil muscle contractile function was examined in ti le anterior latissimus dorsi (ALD) muscle of Japanese quails aged 8 we eks (young adults), 26 weeks, 60 weeks, or 90 weeks (old birds). In vi tro contractile measures of the ALD were made at 25 degrees C (stimulu s 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 1 68 +/- 18 ms). Similarly, one-half relaxation time of the twitch was i ncreased in the ALD from old birds (221 +/- 17 ms) relative to adult b irds 8-26 weeks (173 +/- 11). Aging produced a greater fusing of twitc hes at stimulation frequencies of 5 and 10 Hz, and this resulted in a leftward shift of the force-frequency curve at these frequencies. Shor tening velocity measured by the force-velocity method (Vmax) decreased from 2.6 +/- 0.2 muscle length/s (mL/s) to 1.19 +/- 0.02 mL/s in 8 an d 90-week-old muscles, respectively. Maximal velocity of unloaded shor tening as measured by the slack rest decreased from 3.6 +/- 0.7 mL/s t o 2.4 mL/s in 8-week-old and 90-week-old muscles, respectively. Maxima l tetanic force (60.6 +/- 3.1 mN) and specific force (11.3 +/- 0.3 N/c m(2)) were similar in young adult and old muscles. These data indicate that aging induces a slowing of both twitch contractile characteristi cs and shortening velocity in tire ALD, without affecting maximal forc e capabilities.