Previously, we have shown in experiments with isolated mitochondria that almitrine, a drug used for patients with chronic lung disease, affects the H+/ATP stoichiometry of the F,F,-ATPase [Rigoulet, M., Fraisse, L., Ouhabi, R., GuCrin, B., Fontaine, E. & Leverve, X. M. (1990) Biochim. Biophys. Actu 1018, 91-97]. In the present study, we have investigated the effect of almitrine on gluconeogenesis and oxygen consumption in isolated hepatocytes. Almitrine decreased both the cytosolic and mitochondrial ATP/ADP ratios but had no effect on oxygen consumption in cells incubated with and without octanoate. This must have been due to a double effect. On the one hand, a decrease in the ATP/ADP ratio decreases ATP utilization; on the other hand, in the presence of almitrine more oxygen is required to synthesize ATP. Almitrine did affect gluconeogenesis from various substrates (lactate + pyruvate, glycerone or fructose), but had no effect on glycerol or glutamine metabolism. The effect on gluconeogenesis from glycerone was due to an increase in glycolytic flux. The rate of lactate + pymvate production increased whereas there was no effect on glycerone utilization. This effect was caused by an activation of pyruvate kinase. Our data indicate that this enzyme is an extremely sensitive sensor of the cytosolic ATP/ADP ratio. Hence, under our experimental conditions, the cytosolic ATP/ADP ratio decrease affects only the balance between glucose and lactate + pyruvate productions, and not the phosphorylation of glycerone, the first and controlling step of this pathway.Almitrine is a drug which is used for the treatment of patients suffering from hypoxia due to chronic lung diseases [l , 21. The increase in arterial blood oxygen pressure in patients treated with this drug is mainly explained by a specific effect on chemoreceptors [3-61 and/or by changes in the ventilatiodperfusion ratio [7, 81. Moreover some effects on coupling between oxidation and phosphorylation in brain mitochondria isolated from senescent rats have been reported: an increase at low almitrine concentrations and a decrease at high almitrine concentrations [9].Recently we have described the effects of almitrine in mitochondria isolated from yeast, bovine heart and rat liver [lo, 111. Briefly, almitrine (a) inhibited ATPase activity, (b) decreased the ATP/O ratio without any change in the magnitude of the protonmotive force and (c) had no direct effect on respiratory chain activity. Moreover the number of H' ions transferred by ATPase/mole hydrolyzed ATP increased. Taken together, these properties led us to propose that almitrine acts by changing the mechanistic stoichiometry of mitochondria] ATPase/ATP synthase.The purpose of the present work was to investigate the effects of almitrine in intact rat hepatocytes. As expected from our previous results in isolated rat liver mitochondria, almitrine decreases cytosolic and mitochondrial ATP/ADP ratios without changing the respiratory rate. This unique property of almitrine (i.e. changing the oxidative ATP proCorrespo...

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