INSULIN, KETONE-BODIES, AND MITOCHONDRIAL ENERGY TRANSDUCTION

Addition of insulin or a physiological ratio of ketone bodies to buffe r with 10 mM glucose increased efficiency (hydraulic work/energy from O-2 consumed) of working rat heart by 25%, and the two in combination increased efficiency by 36%. These additions increased the content of acetyl CoA by 9- to 18-fold, increased the contents of metabolites of the first third of the tricarboxylic acid (TCA) cycle 2- to 5-fold, an d decreased succinate, oxaloacetate, and aspartate 2- to 3-fold. Succi nyl CoA, fumarate, and malate were essentially unchanged. The changes in content of TCA metabolites resulted from a reduction of the free mi tochondrial NAD couple by 2- to 10-fold and oxidation of the mitochond rial coenzyme Q couple by 2- to 4-fold. Cytosolic pH, measured using P -31-NMR spectra, was invariant at about 7.0. The total intracellular b icarbonate indicated an increase in mitochondrial pH from 7.1 with glu cose to 7.2, 7.5, and 7.4 with insulin, ketones, and the combination, respectively. The decrease in Eh(7) of the mitochondrial NAD couple, E h(NAD+/NADH)(7), from -280 to -300 mV and the increase in Eh(7) of the coenzyme Q couple, Eh(Q/QH2)(7), from -4 to +12 mV was equivalent to an increase from -53 kJ to -60 kJ/2 mol e in the reaction catalyzed by the mitochondrial NADH dehydrogenase multienzyme complex (EC 1.6.5.3) . The increase in the redox energy of the mitochondrial cofactor coupl es paralleled the increase in the free energy of cytosolic ATP hydroly sis, Delta G(ATP). The potential of the mitochondrial relative to the cytosolic phases, E(mito/cyto), calculated from Delta G(ATP) and Delta pH on the assumption of a 4 H+ transfer for each ATP synthesized, was -143 mV during perfusion with glucose or glucose plus insulin, and de creased to -120 mV on addition of ketones. Viewed in this light, the m oderate ketosis characteristic of prolonged fasting or type II diabete s appears to be an elegant compensation for the defects in mitochondri al energy transduction associated with acute insulin deficiency or mit ochondrial senescence.