Generation of tension by glycerol-extracted vertebrate skeletal muscle fibres in the absence of calcium

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Abstract
When a small bundle of glycerol-extracted fibres from either frog, tortoise or rabbit skeletal muscle was first exposed to high MgATP (5mm) in the absence of Ca2+ (2+-free tension was dependent on the ionic strength in the range 0.04–0.10, on the temperature in the range 6–20° C and the free Mg2+ in the range 0–6mm. It was promoted by low ionic strength, low Mg2+ and high temperature, and was unaffected by varying the MgATP2− in the range 0.4–4mm and by adding ATP regenerating components. A separate regime of tension generation was detected at MgATP2− concentrations of less than 0.1mm, in which MgATP2− concentration was critical. The results are interpreted on the assumption that binding of Mg2+ to some component of the regulatory system is necessary to maintain its inhibitory effect in the absence of Ca2+. Ionic strength and temperature, on the other hand, may affect actomyosin directly.