Exchange of structurally bound phosphate in muscular activity

Abstract

1. When rectus abdominis and sartorius muscles of the frog are incubated with (32)P-orthophosphate and subsequently minced, extracted with carbonate-bicarbonate buffer and water, and converted to acetone powders, considerable radioactivity remains associated with the solid material.2. Muscles labelled with (32)P and subjected to contracture at room temperature with KCl or 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.3. Relaxation of a contracted muscle restores the (32)P content of its acetone powder at least to the level for a resting, control muscle.4. When two recti are incubated with 5 x 10(-4)M-DNP after labelling with (32)P, subsequent depolarization of one 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 DNP.5. It is concluded that the bound phosphate fraction undergoes exchange during activation, shortening and relaxation of muscle, and may represent a source of energy for muscular activity.