The contribution of the elastic reaction is severely underestimated in studies on myofibril contraction.
We have considered the Huxley-Simmons manoeuvre. On the assumption that the quick release is an elastic process and on the basis of the isometric tension and of the stiffness of the muscle fibre we calculated that the spontaneous release of the fibre requires approximately 43 micros, which is much faster than the observed release, approximately 180 micros. We concluded that the observed quick release is a guided process. After proper selection of the mass and of the stiffness of the system we mimicked the early recovery and noticed that most of the energy required to accomplish the early recovery is supplied by the kinetic energy accumulated during the course of the quick release. We computed that the frequency of the working strokes in the half sarcomere was between 4x10(6) and 40x10(6) s(-1). This is not to say that the ATPase rate constants are accumulative but only that the overall frequency of the working strokes in the half saromere is many orders of magnitude faster than the average ATPase rate constant. With this frequency no part of the Huxley-Simmons manoeuvre, quick release included, escapes the control of the working stroke. This means also that there is no reason to take the early recovery as an indication of the length of the working stroke.
Grazi
Enrico
E
Dipartimento di Biochimica e Biologia Molecolare, Università di Ferrara, via Borsari 46, 4410 Ferrara, Italy.
Pozzati
Sara
S
Dipartimento di Biochimica e Biologia Molecolare, Università di Ferrara, via Borsari 46, 4410 Ferrara, Italy.
D004548:Elasticity; D009119:Muscle Contraction; D018485:Muscle Fibers, Skeletal / Q000502:physiology; D009210:Myofibrils / Q000502:physiology*