ADENOSINE TRIPHOSPHATE: CHANGES IN MUSCLES DOING NEGATIVE WORK.

Frog sartorius muscles were isolated, treated with 1-fluoro-2, 4-dini-trobenzene at 0 degrees C, then stimulated tetanically at the length in situ and stretched with a Levin-Wyman ergometer during stimulation. The normal adenosine triphosphate breakdown during the tetanus was reduced by about half during the forced stretch. The tension was increased by about 70 percent, but resynthesis of adenosine triphosphate did not occur. Thus, on the basis of A. V. Hill's results, adenosine triphosphate is probably not the direct final energy source for muscular contraction, although it intimately participates in the process. The use of adenosine triphosphate during negative work was less than one-tenth that needed for positive work.