Summary
The effects of “Ca-free” salines were tested in frog skeletal muscle fibres. It was found that the decrease of the (Ca) in the saline from 1.8 mM to about 3.2×10−10 M (with 4 mM Mg present) did not change the resting potential of the fibres and the depolarizations induced by 40 and 80 mM K. The action potentials, however, were significantly reduced in amplitude and duration by 24% and 33% respectively. K contractures induced with a 117 mM KCl saline had a peak and a slow component. The exposure of the fibres to a “Ca-free” saline [(Ca)ca. 1.6×10−9M] for 40 sec reduced the slow component to 39±16.5% (mean±s.e; 6 fibres) of the control value. The peak component, on the other hand, was slightly decreased to 78±10.5%. These effects were reversible.
The inhibition of the K contractures by extremely low (Ca)o cannot be explained by an alteration of the electrical properties of the muscle fibres or by a depletion of the Ca content of the sarcoplasmic reticulum. It is postulated that the drastic removal of external Ca reduces the driving force for a Ca influx that may take place during the excitation of the muscle and that may be essential for the excitation-contraction coupling.
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This work was supported by grants from the Consejo Nacional de Investigaciones Científicas y Técnicas, Argentina (CONICET) and, partially, from the USPHS (ROI-NS 06935-03NEUA).
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Stefani, E., Chiarandini, D.J. Skeletal muscle: Dependence of potassium contractures on extracellular calcium. Pflugers Arch. 343, 143–150 (1973). https://doi.org/10.1007/BF00585709
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DOI: https://doi.org/10.1007/BF00585709