THE EFFECT OF ELECTROLYTES ON THE CONTRACTILE ELEMENTS OF MUSCLE

Abstract

The effects of changes in electrolyte concn. on muscles which had been preserved in 50% glycerol or washed in water were studied. The psoas prepn. of Szent-Gyorgyi was used, but smooth and cardiac muscle gave the same results. If the prepns. are immersed in 0.16 [image] NaCl or KC1 and if the electrolyte subsequently is washed out with distilled water, tension rises. This effect is not obtained if solns. of CaCl2 or MgCl2 are used, but is restored by brief immersion in NaCl or KC1 solns. Changes in pH have no effect. Thus divalent cations are-bound more firmly than monovalent ions, but divalent exchange with monovalent ions. After the application of ATP, washing out electrolytes produces a larger and more rapid rise in tension. This effect persists after ATP has been washed out and seems to be due to the removal of a substance which diminishes the dissociation of bound cations. Washing out electrolytes also causes a large increase in transparency and swelling. These effects are also enhanced by previous application of ATP and are abolished or diminished by divalent cations. The rise in tension and the swelling are explained as the result of an increase in the charge of the polar groups of the proteins. Because this mechanism produces only a small degree of shortening, it does not explain normal contraction, but may be a part of this process. The significance of the phenomena descr. in relation to recent theories of the mechanism of muscular contraction is discussed. The observations show that increase in the charge of the contractile proteins causes contraction, not relaxation, as has been commonly assumed.