Adv Exp Med Biol
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The elasticity of the connecting filament--the filament that anchors the thick filament to the Z-line--has been investigated using rigor release, freeze-break and immunolabelling techniques. When relaxed insect flight muscle was stretched and then allowed to go into rigor, then released, the recoil forces of the connecting filaments caused sarcomeres to shorten. Thin filaments, prevented from sliding by rigor links, were found crumpled against the Z-line. ⋯ When the frozen sarcomeres were broken along the A-I junction, the broken connecting filaments retracted to the N1-line level, independently of the thin filaments, demonstrating the basic elastic nature of these filaments. To study the elastic properties of the connecting filaments along the sarcomere, the muscle was labelled with monoclonal antibodies against a titin epitope near the N1-line, and another very near the A-I junction in the I-band. Before labelling, fibers were pre-stretched to varying extents.(ABSTRACT TRUNCATED AT 250 WORDS)