Abstract
Actomyosin (AM) was isolated from the heart muscles of normal dogs and dogs with right-sided congestive failure, and also from posoas muscles of rabbits. Action of ouabain on supcrprecipitation, AM-ATPase activity, and isometric tension of glycerinated fibers was observed under various conditions, and it was concluded that1) lower concentrations (therapeutic dose) of ouabain accelerated superprecipitation, and unaffected both ATPase activity and tension-development of glycerinated fibers (in Ca-free medium), 2) in higher concentrations (toxic dose), ouabain inhibited all of the physicochemical properties of AM examined, 3) ouabain had some correlation with Ca in regard to tension-development of glycerinated fibers, since in low concentrations it counteracted the inhibitory effect of Ca, and in high concentrations it augmented this inhibition, and that4) all of the properties of AM extracted from cardiac, both normal and failing, and skeletal muscles had the similar response to this drug. Thus the improvement of the impaired superprecipitation, ATPase activity and tension-development was not observed by the treatment with ouabain.