Abstract

1 . The oxygen consumption of cat cardiac slices of the left ventricle was measured and the changes produced under the influence of various ions and cardiac glycosides were observed.

2. The introduction of scilliroside in concentrations of 1.6 x 10^-8 to 5 x 10^-5M two hours after the beginning of measured respiration produced a maintained increase in the rate of oxygen uptake. The effect and rapidity with which this increase occurred were dependent on the concentration of scilliroside. A concentration of 1 x 10^-6M produced maximal effects. Digitoxin and ouabain in this concentration produced similar results. The oxygen consumption of the papillary muscle of the right ventricle was accelerated by a concentration of 1 x 10^-6M, but not by a concentration of 3.2 x 10^-8M scilliroside.

3. The degree of acceleration of respiration increased as the concentration of added glucose was increased up to 0.2 per cent.

4. The presence of calcium ion was essential to the acceleration of respiration by the cardiac glycosides. When calcium was absent from the medium, the introduction of cardiac glycosides caused a decrease in respiration of cardiac tissue.

5. At a low phosphate concentration the initial respiration was approximately 50 per cent lower than usual. The introduction of scilliroside led to a 75 per cent increase in the rate of oxygen uptake, compared to a 50 per cent increase at higher phosphate concentration. When the concentration of phosphate was low and that of calcium was high the introduction of scilliroside led to a relative acceleration of 150 per cent in the rate of oxygen uptake.

6. Tissues in a medium containing magnesium in concentrations of 1.08 or 2.16 mM, consumed initially less oxygen than when magnesium was absent. The introduction of scilliroside led to a greater relative acceleration in uptake in the presence of magnesium.

7. Hyporespiring tissues showed a relatively greater acceleration in respiration after the introduction of scilliroside than did normally respiring slices.