Key result
New nanonewton-force instrument confirms myofibrillar mechanical properties align with intact muscle fiber studies.
A new instrument allows for precise mechanical characterization of single or small bundles of myofibrils, demonstrating that fiber mechanics are a simple summation of individual sarcomere properties.
Confirms sarcomere summation governs fiber mechanics; leaves open translation to human cardiac muscle or clinical settings.
A new instrument, based on a technique described previously, is presented for studying mechanics of micron-scale preparations of two to three myofibrils or single myofibrils from muscle. Forces in the nanonewton to micronewton range are measurable with 0.5-ms time resolution. Programmed quick (200-microseconds) steps or ramp length changes are applied to contracting myofibrils to test their mechanical properties. Individual striations can be monitored during force production and shortening. The active isometric force, force-velocity relationship, and force transients after rapid length steps were obtained from bundles of two to three myofibrils from rabbit psoas muscle. Contrary to some earlier reports on myofibrillar mechanics, these properties are generally similar to expectations from studies on intact and skinned muscle fibers. Our experiments provide strong evidence that the mechanical properties of a fiber result from a simple summation of the myofibrillar force and shortening of independently contracting sarcomeres.
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Friedman et al. (1996) studied this question. New instrument for studying mechanics of micron-scale preparations of myofibrils was evaluated on Active isometric force, force-velocity relationship, and force transients. A new instrument capable of measuring nanonewton to micronewton forces demonstrated that myofibrillar mechanical properties are similar to expectations from studies on intact and skinned muscle fibers.
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