Evidence that mitochondrial phosphate is visible in 31P NMR spectra of isolated, perfused rat hearts.

We have previously found (P. B. Garlick, T. R. Brown, R. H. Sullivan and K. Ugurbil, J. Mol. Cell Cardiol. 15, 855-858 (1983)) that two peaks could be observed in the phosphate region of NMR spectra of isolated, perfused rat hearts. Upon valinomycin treatment, an increase in the peak at 2.8 ppm in the phosphate region (phosphocreatine set at -2.52 ppm) had been observed. We have now confirmed our hypothesis that this peak originates from the mitochondrial phosphate by: (i) determination of myocardial mitochondrial phosphate contents using density gradient centrifugation in non-aqueous solvents; and (ii) quantitative electron microscopy of the heart tissue. Thus, we conclude that mitochondrial and cytosolic phosphate can be distinguished from each other in 31P NMR spectra of isolated, perfused rat hearts.