Phosphocreatine and oxidative metabolism-contraction coupling in rabbit aorta

Oxidative metabolism-contraction coupling was studied in single rabbit aortic rings by measuring changes in phosphocreatine (PCr) and ATP content, the ratio of PCr to free creatine (Cr), and changes in muscle force under conditions in which cellular energy production was inhibited. We compared rings with markedly different total PCr content by using rings loaded with creatine, control (unloaded) rings, and rings exposed for 30 min to zero-glucose solution. Creatine loading resulted in increases in PCr content to 300% of control. Maintained muscle force generated by 30 microM norepinephrine was decreased by hypoxia, 0.05 and 0.1 mM cyanide, removal of glucose from the bathing media, or glucose removal plus hypoxia. There was no difference between creatine-loaded and unloaded rings in the mechanical effects of these perturbations. Changes in muscle force induced by inhibition of energy production using the various perturbations correlated with changes in PCr/Cr. Data are consistent with oxidative metabolism-contraction coupling being regulated by energy delivery to a reaction or reactions controlling muscle force. Metabolism-contraction coupling is not controlled by total energy stores or by PCr or Cr concentration.