Role of Na+-K+-ATPase in insulin-induced lactate release by skeletal muscle.

International audienceHyperinsulinemia increases lactate release by various organs and tissues. Whereas it has been shown that aerobic glycolysis is linked to Na+-K+-ATPase activity, we hypothesized that stimulation by insulin of skeletal muscle Na+-K+-ATPase is responsible for increased muscle lactate production. To test this hypothesis, we assessed muscle lactate release in healthy volunteers from the [13C]lactate concentration in the effluent dialysates of microdialysis probes inserted into the tibialis anterior muscles on both sides and infused with solutions containing 5 mmol/l [U-13C]glucose. On one side, the microdialysis probe was intermittently infused with the same solution additioned with 2.10(-5) M ouabain. In the basal state, [13C]lactate concentration in the dialysate was not affected by ouabain. During a euglycemic-hyperinsulinemic clamp, [13C]lactate concentration increased by 135% in the dialysate without ouabain, and this stimulation was nearly entirely reversed by ouabain (56% inhibition compared with values in the dialysate collected from the contralateral probe). These data indicate that insulin stimulates muscle lactate release by activating Na+-K+-ATPase in healthy humans

Cyclosporin A inhibits hypoxia-induced pulmonary hypertension and right ventricle hypertrophy.

International audienceRATIONALE: Hypoxia-induced pulmonary hypertension involves hypoxia-inducible factor-1alpha (HIF-1alpha) activation as well as elevated resting calcium levels. Cyclosporin A (CsA) inhibits calcium-induced calcineurin activation and blocks the stabilization of HIF-1alpha in cultured cells. OBJECTIVES: We hypothesized that treatment of rats with CsA would prevent HIF-1-dependent gene transcription, lower specific responses to acute hypoxia, and prevent pulmonary hypertension and right ventricle hypertrophy resulting from prolonged exposure to hypoxia. METHODS: Acute and chronic responses to hypoxia were studied in rats treated or not treated with CsA (25 mg x kg(-1) x d(-1)). MEASUREMENTS: Transcript levels of genes encoding the serotonin transporter or four HIF-1 target genes, in rats exposed for 6 h to ambient hypoxia, treated or not by CsA, were measured. In vivo hemodynamics, hematocrit, and heart morphologic characteristics were assessed in rats subjected to hypoxia for 3 wk, treated or not treated with CsA. Changes in mRNA levels of the modulatory calcineurin-interacting protein-1 (MCIP-1) were used as a sensitive indicator of calcineurin activity in lung and heart. MAIN RESULTS: Acute exposure to hypoxia led to a marked increase in mRNA levels of serotonin transporter, modulatory calcineurin-interacting protein-1, and HIF-1 target genes, which was blunted by CsA treatment. Prolonged exposure to hypoxia raised right ventricle pressure, induced right ventricle hypertrophy, and activated cardiac calcineurin, effects that were fully prevented by CsA treatment. CONCLUSIONS: These results suggest that CsA prevents hypoxia-induced pulmonary hypertension and right ventricle hypertrophy, either by inhibiting HIF-1 transcriptional activity in lung, by decreasing calcineurin activity in lung and heart, by direct effects of CsA, or by a combination of these factors

High dietary sucrose triggers hyperinsulinemia, increases myocardial beta-oxidation, reduces glycolytic flux and delays post-ischemic contractile recovery.

International audienceAlthough the causal relationship between insulin resistance (IR) and hypertension is not fully resolved, the importance of IR in cardiovascular dysfunction is recognized. As IR may follow excess sucrose or fructose diet, the aim of this study was to test whether dietary starch substitution with sucrose results in myocardial dysfunction in energy substrate utilization and contractility during normoxic and post-ischemic conditions. Forty-eight male Wistar rats were randomly allocated to three diets, differing only in their starch to sucrose (S) ratio (13, 2 and 0 for the Low S, Middle S and High S groups, respectively), for 3 weeks. Developed pressure and rate x pressure product (RPP) were determined in Langendorff mode-perfused hearts. After 30 min stabilization, hearts were subjected to 25 min of total normothermic global ischemia, followed by 45-min reperfusion. Oxygen consumption, beta-oxidation rate (using 1-13C hexanoate and Isotopic Ratio Mass Spectrometry of CO2 produced in the coronary effluent) and flux of non-oxidative glycolysis were also evaluated. Although fasting plasma glucose levels were not affected by increased dietary sucrose, high sucrose intake resulted in increased plasma insulin levels, without significant rise in plasma triglyceride and free fatty acid concentrations. Sucrose-rich diet reduced pre-ischemic baseline measures of heart rate, RPP and non-oxidative glycolysis. During reperfusion, post-ischemic recovery of RPP was impaired in the Middle S and High S groups, as compared to Low S, mainly due to delayed recovery of developed pressure, which by 45 min of reperfusion eventually resumed levels matching Low S. At the start of reperfusion, delayed post-ischemic recovery of contractile function was accompanied by: (i) reduced lactate production; (ii) decreased lactate to pyruvate ratio; (iii) increased beta-oxidation; and (iv) depressed metabolic efficiency. In conclusion, sucrose rich-diet increased plasma insulin levels, in intact rat, and increased cardiac beta-oxidation and coronary flow-rate, but reduced glycolytic flux and contractility during normoxic baseline function of isolated perfused hearts. Sucrose rich-diet impaired early post-ischemic recovery of isolated heart cardiac mechanical function and further augmented cardiac beta-oxidation but reduced glycolytic and lactate flux

On the regulation of cellular energetics in health and disease.

International audienceVery recent experimental data, obtained by using the permeabilized cell technique or tissue homogenates for investigation of the mechanisms of regulation of respiration in the cells in vivo, are shortly summarized. In these studies, surprisingly high values of apparent Km for ADP, exceeding that for isolated mitochondria in vitro by more than order of magnitude, were recorded for heart, slow twitch skeletal muscle, hepatocytes, brain tissue homogenates but not for fast twitch skeletal muscle. Mitochondrial swelling in the hypo-osmotic medium resulted in the sharp decrease of the value of Km for ADP in correlation with the degree of rupture of mitochondrial outer membrane, as determined by the cytochrome c test. Very similar effect was observed when trypsin was used for treatment of skinned fibers, permeabilized cells or homogenates. It is concluded that, in many but not all types of cells, the permeability of the mitochondria outer membrane for ADP is controlled by some cytoplasmic protein factor(s). Since colchicine and taxol were not found to change high values of the apparent Km for ADP, the participation of microtubular system seems to be excluded in this kind of control or respiration but studies of the roles of other cytoskeletal structures seem to be of high interest. In acute ischemia we observed rapid increase of the permeability of the mitochondrial outer membrane for ADP due to mitochondrial swelling and concomitant loss of creatine control of respiration as a result of dissociation of creatine kinase from the inner mitochondrial membrane. The extent of these damages was decreased by use of proper procedures of myocardial protection showing that outer mitochondrial membrane permeability and creatine control of respiration are valuable indices of myocardial preservation. In contrast to acute ischemia, chronic hypoxia seems to improve the cardiac cell energetics as seen from better postischemic recovery of phosphocreatine, and phosphocreatine overshoot after inotropic stimulation. In general, adaptational possibilities and pathophysiological changes in the mitochondrial outer membrane system point to the central role such a system may play in regulation of cellular energetics in vivo