Exchange of structurally bound phosphate in muscular activity

Abstract

Considerable radioactivity remains associated with the solid material when the rectus-abdominis and sartorius muscles of the frog are incubated with p32-orthophosphate and subsequently minced, extracted with carbonate-bicarbonate buffer and water and converted to acetone powders. Muscles labelled with P32 and subjected to contracture at room temperature with KCl or acetylcholine (ACh) yield acetone powders which, in comparison with those of uncontracted control muscles, show a significantly decreased radioactivity. There is no evidence for a corresponding decrease in the total phosphate content. Relaxation of a conducted muscle restores the P32 content of its acetone powder at least to the level for a resting control muscle. When 2 recti are incubated with 5 x 10-4 M-DNP after labelling with P32, subsequent depolarization of 1 muscle with KCl usually results in an increase in the activity of the bound phosphate fraction, with little or no contracture in addition to that already caused by the dinitrophenol DNP. The bound phosphate fractionwhich probably undergoes exchange during activation, shortening and relaxation of muscle may represent a source of energy for muscular activity.