31P NMR measurement of ATP synthesis rate in perfused intact rat hearts.

Using 31P NMR and the saturation-transfer method, the unidirectional rate of ATP synthesis was measured in isolated, Langendorff-perfused, isovolumic rat hearts operating at a rate pressure product of 25.6 +/- 2.5 (SE) X 10(3) mmHg X min-1 and consuming O2 at a rate of 35 +/- 2 mumol O2 X min-1 X (g dry wt)-1, at 37 degrees C. This rate was 7.2 +/- 0.9 mumol X s-1 X (g dry wt)-1 and was related to the rate of oxygen atom consumption by a ratio of 6.3 +/- 0.9. These data show that in the intact heart the unidirectional rate of ATP synthesis exceeds the net rate of ATP synthesis and consumption by approximately a factor of 2.