Oscillating contractions in protoplasmic strands of Physarum: effects of externally applied ouabain, sodium-, potassium- and calcium-ions.

1. Concentrations of 0.1-10 mM Ouabain do not affect oscillating contractions, when applied externally in physiological solutions. 2. Ouabain has no effect, when applied in solutions of increased sodium- (100 mM) and lowered potassium-concentration (0.1 or zero mM). 3. De novo generation of oscillating contractions in protoplasmic drops is not suppressed in Ouabain-solutions. 4. Biochemical studies of Na-K-ATPase did not show any Ouabain sensitive ATPase-activity. 5. Reaction of veins on high concentrations (300 mosm) is discussed as to be a physical effect. 6. It is concluded that no Na-K-ATPase is engaged in triggering oscillating contraction automaticity.