Biochemistry of adenosine triphosphatase activity of avian fast and slow muscle

Abstract

The posterior latissimus dorsi (PLD), a pure twitch muscle, and the anterior latissimus dorsi (ALD), a pure tonus muscle, of the chicken were examined for a comparison of their actomyosin adenosine triphosphatase (AM-ATPase) activity. Other investigators have determined that the PLD contracts six to eight times faster than the ALD. The AM-ATPase activity of the PLD is only 1.4 times that of the ALD, which does not account for the difference in contraction times. Rather, the morphological differences between the two muscles are proposed as the basis for the difference in speeds of contraction. The well-developed SR and T system in the PLD provide a more rapid and efficient excitation-contraction coupling than in the ALD. The effects of cyclic adenosine 3′,5′-monophosphate (cAMP) on these muscles were studied, and found to inhibit the AM-ATPase and lower the optimal ATP concentration. Rabbit skeletal muscle was studied for comparison, and cAMP was again found to inhibit the AM-ATPase. However, there was a differential inhibition of the fast and slow twitch muscles; the fast twitch muscles were inhibited to a greater degree than the slow twitch.