Mechanism of Relaxation in Extracted Muscle Fibers

Abstract

In muscle fibers from the psoas of the rabbit preserved in 50% glycerol, low concns. of ATP cause contraction, high concns. cause relaxation. Also inorganic pyrophosphate and urea cause rapid relaxation. These relaxing agents make the muscle very distensible, plastic and translucent. It is concluded that the effect of these substances is caused by the breaking up of bonds within the contractile elements and that relaxation is a passive process. Tension is not maintained in the absence of ATP, suggesting that a continuous energy supply is necessary for the maintainance of tension. These findings disagree with theories which assume that muscular contraction is due to the utilization of kinetic energy.