Acta Biochimica et Biophysica 16. (1981)
1981 / 3-4. szám - Proceedings of the Eleventh Conference on Biophysics. Abstracts
Proceedings of the 11th Conference of Biophysics 237 1. In the intact fibres the shortening of myofibrils corresponded to the sliding filament model. In supercontracted state contraction bands were formed around the Z lines. 2. In some fibres damaged by slight ischemic effect, where the ischemic injury mainly restricted to the sarcolemma and caused redistribution of the diffusible elements, the muscle shortening in supercontracted state was manifest in a real A band shortening only. The sarcomeres became thicker and the length of A bands shortened to the half without any contraction bands around the Z lines. A single myofibril could contain both shorter and normal A bands facing one another. This findings prove that myosin filaments are capable of shortening during muscle contraction but, of course, this shortening may be an irreversible process. The Structural Basis of “Stretch Activation” in the Insect Flight Muscle K. Trombitás, Anna Tigyi-Sebes Central Laboratory, Medical University, Pécs In the Ca2+ activated state of the insect flight muscle small applied length changes result in large changes both in maintained tension and maintained ATPase activity. This phenomenon of muscle activation is termed “stretch activation”. C filaments are supposed to play an important role in stretch activation of fibrillar muscle. In order to support this hypothesis the following experiments were performed : The glycerol-extracted flight muscle of bee (Apis mellifica) was stretched in rigor solution. Since the sliding movement of the filaments had been inhibited stretch broke away the actin filaments from one of the Z lines asymetrically in some sarcomeres and only the C filaments strained the myosin filaments in the broken half sarcomere. After the stretch the broken actin filaments remained in their original position. When the muscle was transferred to activated solution the developed tension was as high as to force the broken actin filaments to move through the M line producing a wide double overlap zone in the intact half sarcomere. Very often the broken actin filaments slided through the M line completely from one half of the sarcomere into the other in such a way that the intact half sarcomere became a total double overlap zone, while in the broken half sarcomere the half A band became similar to an H-zone. But when the muscle stretched in rigor was released and then treated with activated solution the broken actin filaments maintained their original position, or their movement toward the M line was strongly limited producing, thus, very narrow double overlap zone. The findings of our experiments support the idea that the strain of the myosin filaments caused by the C filaments results in stretch activation. Acta Biochimica et Biophysica Academiae Scientiarum Hungaricae 16, 1981