Adenosine triphosphate compartmentation in the rat heart: a 31P spin-lattice relaxation study

Longitudinal relaxation times (T1) of phosphorus compounds in the perfused rat heart and erythrocytes were measured using the 31P Driven-Equilibrium Single-Pulse Observation of T1 relaxation (DESPOT) method at 33 degrees C. Both creatine phosphate in the heart and the three phosphate groups of adenosine triphosphate (ATP) in erythrocytes showed single-exponential relaxation. The three phosphate groups of ATP in the heart, however, had two T1 components. The T1 values of the short and the long T1 components of the beta-phosphate of ATP were ca. 0.4 and 14 s, respectively. The fraction with the long T1 represented ca. 30% of the total ATP content. These results suggested that there were two major pools of intracellular ATP in the rat heart which could be determined by 31P NMR spectroscopy.