Resting muscle concentrations of ATP and phosphocreatine did not change.

During cardioplegia, myocardial ATP and phosphocreatine contents increased and glycogen concentration tended to decrease.

Significant correlations were observed between endomyocardial and transmural adenine nucleotide and glycogen contents but not phosphocreatine content.

Creatine, a nitrogenous organic acid, replenishes cytoplasmic ATP at the expense of mitochondrial ATP via the phosphocreatine shuttle.

CKMT1 inhibition altered mitochondrial respiration and ATP production, an effect that was abrogated by phosphocreatine-mediated reactivation of the arginine-creatine pathway.