Figure/Graphic 1: End-diastolic - End-systolic
Movement from end-diastolic to end-systolic state of the sarcomere involves major changes in structural status of cardiac titin. Enddiastolic stretch requires uncoiling of Ig-like segments, PEVK sequence and N2B/N2BA regions. As the contraction starts with actin-myosin interaction, the recoil spring forces of stretched titin molecules support shortening of the sarcomere until the titin has no more stretched segments. At this moment, the "molecular spring" is inactive and the "slack sarcomere" status is achieved. Continuation of active contraction beyond this point requires Ig-like segments of titin to be stretched inwards, creating spring forces ready to initiate diastole when active actinmyosin interaction will cease.