Evidence from insect fibrillar muscle about the elementary contractile process.

Bundles of myofibrils prepared from the dorsal longitudinal flight muscles of giant water bugs show oscillatory contractile activity in solutions of low ionic strength containing ATP and 10(-8)-10(-7)M Ca(2+). This is due to delay between changes of length and changes of tension under activating conditions. The peculiarities of insect fibrillar muscle which give rise to this behavior are (1) the high elasticity of relaxed myofibrils, (2) a smaller degree of Ca(2+) activation of ATPase activity in unstretched myofibrils and extracted actomyosin, and (3) a direct effect of stretch on ATPase activity.