THE RELATIONSHIP OF FORCE OF CONTRACTION TO HIGH-ENERGY PHOSPHATE IN HEART MUSCLE

¹ Department of Pharmacology, Cornell University Medical College, New York 21, N. Y.

1. Papillary muscles from the right heart of the cat were analyzed for phosphocreatine, inorganic phosphate, total acid-soluble phosphate, and the adenosine nucleotides, under several conditions affecting the force of their contraction. There were 56 muscles in all. Enzymatic methods were used for separating ATP, ADP, and AMP.

2. ATP was decreased in papillary muscles which showed more than 50 per cent decline in systolic force after having been made to contract in a bath of oxygenated, phosphate-buffered Ringer's solution. In these, PC was normal.

3. ATP was normal in papillary muscles treated as above, but in which the systolic force was restored by ouabain.

4. A decline in contractile force of papillary muscles produced by anoxia was associated with a decrease in ATP similar to that in well-oxygenated muscles in which analagous decline in systolic force had taken place, but in the anoxic muscles the PC disappeared.

5. These data suggest that the decline in systolic force of the papillary muscle is due to the fall in concentration of ATP, and that digitalis improves contractile force by restoring the ATP. The presence of abundant phosphocreatine suggests that the fall in ATP is not the result of insufficient high-energy phosphate, but a deficiency of total adenosine nucleotide, and it may be one of the actions of digitalis to restore adenosine nucleotide to normal levels.