Changes of adenosine triphosphatase activity and tension with fibre elongation in glycerinated insect fibrillar flight muscle

Abstract

1. The relationship between fibre elongation and the CA2+-activated ATPase of glycerinated insect fibrillar muscle has been studied. 2. The A-filaments in insect fibrillar muscle are directly strained in a Ca2−-free solution in the absence of permanent actin-myosin interactions. Strain increases the sensitivity of the fibres to low levels of Ca2+. 3. Both ATPase and tension increase up to a fibre extension of 10%; above this fibre length no further strain can be applied to the A-filaments. Between 10% and 20% stretch both tension and ATPase reach a plateau. 4. At fibre elongations greater than 20% both fibre tension and ATPase activity decrease again corresponding to the reduction in the overlap between the A-and I-filaments.