Filament geometry and the activation of inisect flight muscles

摘要: HIGH wingbeat frequencies are required for flight in many insects, and have led to striking specialisations1. The thorax wings form a resonant system whose oscillation is sustained by alternating contractions of antagonistic muscles. action these muscles produce only small-amplitude deformation the thorax, mechanically amplified into wing movements. diverse arrangement1 ultrastructure2. In several insect orders, they characteristic ‘fibrillar’ type very regular architecture well known3. As recognised largely through work Pringle4, certain properties fibrillar muscle permit more rapid wing-beats because does not depend on pacemaking neural input: receive slow irregular stimulation, contraction each triggered, after delay, directly stretch applied it while its antagonist shortens. Studies isolated glycerol- extracted fibres show that unusual underlying this sensitivity intrinsic contractile apparatus itself5. ATPase levels tension low calcium-activated at rest length, but increased slight extension (0.1–5%). exhibit both actin-linked myosin-linked regulation typical invertebrate muscles6, additional regulatory effects mechanical conditions understood. Stretch has been presumed modify cross-bridge attachment some unknown effect myosin filamenats4 (possibly transmitted structures which connect them Z-line muscles7). I suggest here aspects stretch–activation may be explained particular geometry their actin filaments.