Temperature‐dependent calcium sensitivity changes in skinned muscle fibres of rat and toad.

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Abstract
Single mechanically skinned muscle fibers of different types (fast- and slow-twitch mammalian; slow and twitch amphibian) were successively activated in solutions of various Ca2+ concentrations at different temperatures. An increase in temperature from 5.degree. to 22.degree. C reversibly shifted the isometric steady-state force-pCa curves towards higher Ca2+ concentration for individual fibers of each of the muscle types. A further increase in temperature to 35.degree. C in mammalian fibers resulted in an additional decrease in Ca2+ sensitivity. The temperature dependence of Ca2+ sensitivity was greater in the faster fiber types: fast-twitch > slow-twitch > slow. The maximum isometric force response, PO, of both rat and toad skinned fibers was strongly dependent on temperature < 22.degree. C. No detectable force could be induced by Ca2+ in mammalian muscle fibers at 0-1.degree. C while in toad fibers PO decreased by .apprx. 90% when temperature dropped from 20.degree. to 0.degree. C. Since in mechanically skinned fibers of other amphibians (Bufo bufo, Rana spp.) PO is only marginally affected it is likely that the PO-temperature relations are indicative of the range of temperature over which the muscles are normally functional. The PO-temperature relations of skinned muscle fibers closely resembled the PO-temperature relations of tetanically stimulated intact muscle preparations from the same species of animals suggesting that the contractile apparatus is mainly responsible for the variation of force response with temperature in intact muscle.