Abstract
CONTRACTILE responses are depressed and may be abolished in muscles that are shrunken by exposure to hyperosmotic media; they are enhanced when the muscles are swollen in hyposmotic media1–4. The effects of hyperosmotic solutions have been ascribed5 to “dissociation of electromechanical coupling”, but earlier work4,6 had shown that the processes of excitation–contraction coupling were unaffected. Howarth4 therefore proposed two alternative mechanisms. He suggested that the movement of water into or out of the cell in the different osmotic conditions (i) may modify the viscosity of the myoplasm, or (ii) may affect the contractile machinery by the associated changes in the intracellular ionic strength. In our experiments, intracellular applications of calcium were used to activate contraction; thus they bypassed the factor of e–c coupling. Furthermore, they were designed so as to discriminate between effects on the volume of the fibres and on the ionic strength of the intracellular phase which are both a result of changes in water content. The results demonstrate that the predominant and, perhaps, the only factor affecting the tension is the change in ionic strength. Only data on ionophoretic applications of calcium are reported here, but similar findings have also been obtained with other agents that activate contractile responses7.
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APRIL, E., BRANDT, P., REUBEN, J. et al. Muscle Contraction: the Effect of Ionic Strength. Nature 220, 182–184 (1968). https://doi.org/10.1038/220182a0
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DOI: https://doi.org/10.1038/220182a0
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