ION EFFECTS ON MUSCULAR FATIGUE AND THEIR INDEPENDENCE OF CHANGES IN THE METABOLISM OF MUSCLES

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Abstract
Isometric contractions were recorded in nerve muscle preparations of Rana esculenta stimulated indirectly by barely maximal faradic currents until fatigue occurred. Stimulation periods (5-30 sec.) and rest periods (2-5 min.) alternated. Under these conditions 2 homologous muscles of the same frog give almost identical tensions. A Ringer''s solution containing an excess of Ca greatly delays fatigue. This phenomenon is independent of fundamental changes in the metabolism of the muscle, since it is obtained in oxygenated solutions, in the presence of KCN which suppresses the utilization of O, and after poisoning with monobromo-acetic acid (suppression of lactic acid formation). The experiments seem to indicate that the delay in fatigue is chiefly due to physico-chemical alterations of the surface layer of muscle cells (decrease in permeability) although an influence of Ca on the anaerobic phase of muscular metabolism is possible. When CaCl2 is replaced by equimolar concentrations of either SrCl2 or BaCl2 or MgCl2, fatigue is greatly enhanced; but these salts bring about a beneficial effect on the muscle (delay in fatigue) which is comparable to the Ca effect described above when they are added to an ordinary Ringer''s solution containing 8.1 M X 10-4 CaCl2.

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