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) × 10³ mmHg · min^-1 and consuming O₂; at a rate of 35 ± 2 μmol O₂ · min^-1. (g dry wt)^-1, at 37°C. This rate was 7.2 ± 0.9 μmol · s^-1 · (g dry wt)^-1 and was related to the rate of oxygen atom consumption by a ratio of 6.3 ± 0.9. These date 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.