Effect of potentiators of muscular contraction on contractile and enzymatic activities of sarcolemma

Sarcolemma tubes isolated from rabbit skeletal muscle exhibit a predominantly radial contraction which can be induced by ATP, Zn2+, and Cd2+ and to a smaller extent by ADP, SCN−, Ca2+ and Mg2+. The contraction is an intrinsic property of the sarcolemma, since it cannot be attributed to osmotic effects or to the activity of adhering myofibrils. Parallel studies on the surface ATPase activity of isolated semitendinosus muscles of the frog show that this enzymatic activity is inhibited reversibly by Zn2+ or Cd2+. The results are related to the twitch potentiating effects of some of the substances tested.