PMID: 6983616Jan 1, 1982Paper

The effects of reducing the extracellular calcium concentration on the twitch in isolated frog's skeletal muscle fibres

The Japanese Journal of Physiology
G B Frank

Abstract

When muscle fibres isolated from the frog's semitendinosus are placed in a calcium-free, bicarbonate buffered Ringer's solution the twitch declines in an irregular stepwise fashion and disappears usually within 1 to 9 min. There is often an initial period of twitch potentiation when the fibres are exposed to 0-Ca2+. Although considerably shorter than the time in 0-Ca2+ required to deplete intracellular calcium stores, the time required to eliminate the twitch is longer than estimates of the minimum time required to remove calcium from the fluid in the t-tubular network by free diffusion. When the calcium concentration was only partially reduced the twitch was potentiated at concentrations between 10 and 50% of the usual concentration in Ringer's. At lower calcium concentrations the potentiation is followed by a reduction, and in some fibres the twitch was eliminated without completely removing the calcium ions from the bathing solution. The results support the hypothesis that there is a store of calcium ions bound to the t-tubular membranes ("trigger calcium") which is required for excitation-contraction coupling during the twitch.

Citations

Sep 7, 2006·Pflügers Archiv : European journal of physiology·Juliet A Usher-SmithChristopher L-H Huang
Mar 1, 1994·Comparative Biochemistry and Physiology. Pharmacology, Toxicology and Endocrinology·M Oz, G B Frank

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