The ATP/ADP-antiporter inhibitors and the substrate ADP suppress the uncoupling effect induced by low (10-20 pM) concentrations of palmitate in mitochondria from skeletal muscle and liver. The inhibitors and ADP are found to (a) inhibit the palmitate-stimulated respiration in the controlled state and (b) increase the membrane potential lowered by palmitate. The degree of efficiency decreases in the order: carboxyatractylate (CAtr) > ADP > bongkrekic acid, atractylate. GDP is ineffective, Mg . ADP is of much smaller effect, whereas ATP is effective at much higher concentration than is ADP. Inhibitor concentrations, which maximally suppress the palmitate-stimulated respiration, correspond to those needed for arresting the state 3 respiration. The extent of the CAtr-sensitive stimulation of respiration by palmitate has been found to decrease with an increase in palmitate concentration. Stimulation of the controlled respiration by p-trifluoromethoxycarbonylcyanide phenylhydrozone (FCCP) and gramicidin D at any concentrations of these uncouplers is CAtr-insensitive, whereas that caused by a low concentrations of 2,4-dinitrophenol and dodecyl sulfate is inhibited by CAtr.The above effect of palmitate develops immediately after addition of the fatty acid. It is resistant to EGTA as well as to inhibitors of phospholipase (nupercain) and of lipid peroxidation (ionol). Moreover, palmitate accelerates spontaneous release of the respiratory control, developing in rat liver mitochondria under certain conditions. This effect takes several minutes, being sensitive to EGTA, nupercain and ionol. Like the fast uncoupling, this slow effect is inhibited by ADP but CAtr and atractylate are stimulatory rather than inhibitory.In artificial planar phospholipid membrane, palmitate does not increase the membrane conductance, FCCP increases it strongly and dinitrophenol only slightly.In cytochrome oxidase proteoliposomes, FCCP, gramicidin and dinitrophenol (less effectively) lower, whereas palmitate enhances the cytochrome-oxidase-generated membrane potential. In this system, monensin substitutes for palmitate.It is concluded that the ATP/ADP antiporter is somehow involved in the uncoupling effect caused by low concentrations of palmitate and, partially, of dinitrophenol, whereas uncoupling produced by FCCP and gramicidin is due to their action on the phospholipid part of the mitochondria1 membrane. A possible mechanism of this effect is discussed.The uncoupling of oxidation and phosphorylation by free (non-esterified) fatty acids has been studied since 1956 [l -111. The first indication that such an effect may be physiologically significant was obtained by our group in 1965 when it was shown that the fatty-acid-mediated uncoupling in skeletal muscle mitochondria is involved in the burst of heat production by cold-exposed pigeons [12]. Later it was reported that thermogenin, the protein responsible for the thermoregulatory uncoupling in brown fat mitochondria, is activated by fatty acids [I 31. Since thermogenin is absent from muscle mito...

The ATP/ADP-antiporter inhibitors and ADP decrease the palmitate-induced stimulation of the mitochondrial respiration in the controlled state.

No abstract