Evidence for an ATP-Actomyosin Complex in Relaxed Muscle and Its Response to Calcium Ions

Abstract

Strands from the psoas muscle of the rabbit, extracted in glycerol, were relaxed by high concns. of ATP. Such fibers remain relaxed for at least 20 min. after the ATP has been washed out by saline containing Mg ions. During this time they respond to Ca ions by rapid contraction. ATP produces rapid relaxation only in the presence of Mg. Ca causes contraction even in the presence of Mg and high concns. of ATP.