The hypodynamic state of the frog heart. Further evidence for a phosphocreatine-creatine pathway.

The hypodynamic state of frog heart has been investigated from the energetic point of view. The amplitude of tension was enhanced when the oxidative metabolism was stimulated by oxygen and pyruvate. However, a time-dependent tension decrease still occurred with both oxygen and pyruvate. Hypodynamia, although slowed down under these conditions, was accompanied by a decrease in CP rather than in ATP. It is shown that the decrease in CP was due to a leak of creatine out of the cell, consequent to the non-equilibration of the oncotic pressure in the perfusion fluid. Creatine (20 mM) or any plasma expander, prevented the fall in both CP and tension. These results are in agreement with the proposal that the CP/CK/Cr system is the major metabolic intermediate between production and use of energy for contraction and that, besides Ca ions, it participates in the regulation of tension. It is suggested that hypodynamia mostly originates in a decreased Ca utilization due to shortage of energy.