Relation between Length of Muscle and Breakdown of Phosphorylcreatine in Isometric Tetanic Contractions

Abstract

RECENT experiments have shown that adenosine tri-phosphate (ATP) is actually utilized by working muscles during single contractions but is normally resynthesized during the contraction by the action of ATP–Cr transphosphorylase and ATP–AMP transphosphorylase (myokinase)^1–4. A breakdown of phosphorylcreatine (PCr) at 0° C during single isotonic contractions has been observed directly in frog rectus abdominis muscles (Rana pipiens) treated with 2,4-dinitrophenol to reduce the high tissue content of this substance. There is a linear relationship between the amount of breakdown and the work performed, with very little PCr utilized in activation and shortening per se of these muscles. The experiments reported here show that rectus abdominis muscles cleave PCr during short isometric tetanic contractions in amounts proportional to the time and to the developed tension.