Abstract

The levels of ATP, ADP, AMP, PC and IP; the Q_o2; the contractile tension and the Na⁺, K⁺ and Ca⁺⁺ content of papillary muscles of cat were measured following the administration of ouabain to the medium containing varying amounts of K⁺ and Ca⁺⁺.

At the inotropic stage of ouabain action, the Q_o2 increased whereas there was no change in either the content of the phosphate compounds or the tissue content of Na⁺, K⁺ and Ca⁺⁺.

At the toxic stage of ouabain action, the Q_o2 was markedly increased while the PC and ATP content were decreased. In addition, the tissue content of K⁺ was decreased whereas that of Na⁺ and Ca⁺⁺ was increased.

Excess Ca⁺⁺ in the medium increased the Q_o2, the tissue content of Ca⁺⁺ and the contractile tension without a concomitant change in the levels of phosphate compounds. The addition of ouabain under this condition was followed by a decrease in the content of PC and ATP with no increase in the contractile tension.

In a Ca⁺⁺-free medium, the contractile tension decreased markedly and the Q_o2 only slightly. The effect of ouabain on all parameters measured was less in Ca⁺⁺-free medium than in the basic medium. Excess K⁺ in the medium has an effect similar to that of no Ca⁺⁺ in the medium.

K⁺-free medium increased the contractile tension and the Q_o2 but decreased the content of ATP and PC and the cellular content of K⁺. The addition of ouabain under this condition was followed by a further decrease in the content of PC and ATP with no increase in the contractile tension.