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Skeletal muscle resists stretch by rapid binding of the second motor domain of myosin to actin

PainSci » bibliography » Brunello et al 2007
Tags: stretch, muscle, biology, neat, exercise, self-treatment, treatment

One article on PainSci cites Brunello 2007: Quite a Stretch

PainSci notes on Brunello 2007:

While it is well understood that muscles have a “braking” function that kicks in with rapid increases in load, something that occurs constantly in normal activity, but the molecular mechanisms for braking has been slow . This super cool study shed quite a bit of light on that old puzzle of muscle physiology, showing that muscles brake not by “contracting” to resist the rapid elongation, but by building many extra actin-myosin bonds in an instant — becoming stiffer and less extensible in just a few milliseconds, like a rubber band that gets instantly thicker in proportion to how suddenly you pull on it.

This process is also requires very little energy. So the muscle basically solidifies efficiently.

original abstract Abstracts here may not perfectly match originals, for a variety of technical and practical reasons. Some abstacts are truncated for my purposes here, if they are particularly long-winded and unhelpful. I occasionally add clarifying notes. And I make some minor corrections.

A shortening muscle is a machine that converts metabolic energy into mechanical work, but, when a muscle is stretched, it acts as a brake, generating a high resistive force at low metabolic cost. The braking action of muscle can be activated with remarkable speed, as when the leg extensor muscles rapidly decelerate the body at the end of a jump. Here we used time-resolved x-ray and mechanical measurements on isolated muscle cells to elucidate the molecular basis of muscle braking and its rapid control. We show that a stretch of only 5 nm between each overlapping set of myosin and actin filaments in a muscle sarcomere is sufficient to double the number of myosin motors attached to actin within a few milliseconds. Each myosin molecule has two motor domains, only one of which is attached to actin during shortening or activation at constant length. A stretch strains the attached motor domain, and we propose that combined steric and mechanical coupling between the two domains promotes attachment of the second motor domain. This mechanism allows skeletal muscle to resist external stretch without increasing the force per motor and provides an answer to the longstanding question of the functional role of the dimeric structure of muscle myosin.

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