Peculiarities of energy exchange in mitochondria of heart exposed to ischemia

Available from VNTIC / VNTIC - Scientific & Technical Information Centre of RussiaSIGLERURussian Federatio

What controls the outer mitochondrial membrane permeability for ADP: facts for and against the role of oncotic pressure

AbstractIn our study 10% of bovine serum albumin was added to the physiological incubation medium to mimic the oncotic pressure of the cellular cytoplasm and to test for its effect on the respiration of isolated rat heart mitochondria, saponin- or saponin plus crude collagenase (type IV)-treated heart muscle fibers and saponin-treated rat quadriceps muscle fibers. Pyruvate and malate were used as substrates. We found that albumin slightly decreased the maximal ADP-stimulated respiration rate only for saponin-treated heart muscle fibers. The apparent Km ADP of oxidative phosphorylation increased significantly, by 70–100%, for isolated heart mitochondria, saponin plus collagenase-treated heart muscle fibers and for saponin-treated quadriceps muscle fibers but remained unchanged for saponin-treated heart muscle fibers. The saponin-treated heart muscle fibers were characterized by a very high control apparent Km ADP value (234±24 μM ADP) compared with other preparations (14–28 μM ADP). The results suggest that in vivo the oncotic pressure is not the relevant factor causing the low outer mitochondrial membrane permeability for ADP in cardiomyocytes, in contrast to quadriceps muscle cells. It is likely that the outer mitochondrial membrane-bound protein(s) which is supposed to remain in saponin-treated heart muscle fibers is responsible for this property of the membrane

Molecular modelling of K/sup ATP/ channel blockers-ADP/ ATP carrier interactions

IEE Proceedings : 12th BTK meeting: "Systems biology: redefining BioThermoKinetics"The modelling of molecule-molecule interactions has been widely accepted as a tool for drug discovery and development studies. However, this powerful technique is unappreciated in physiological and biochemical studies, where it could be extremely useful for understanding the mechanisms of action of various compounds in cases when experimental data are controversial due to complexity of the investigated systems. In this study, based on the biochemical data suggesting involvement of mitochondrial ADP/ATP carrier in K+ and H+ transport to mitochondrial matrix molecular modelling is applied to elucidate the possible interactions between the ADP/ATP carrier and its putative ligands--K(ATP) channel blockers glybenclamide, tolbutamide and 5-hydroxydecanoate. Results revealed that K(ATP) channel blockers could bind to the specific location proximal to H1, H4, H5 and H6 transmembrane helices within the cavity of the ADP/ ATP carrier. Analysis of the predicted binding site suggests that K(ATP) channel blockers could interfere with both the ADP/ATP translocation and possible cation flux through the ADP/ATP carrier, and supports the hypothesis that the ADP/ATP carrier is a target of K(ATP) channel modulatorsKauno medicinos universiteto Biomedicininių tyrimų institutasVytauto Didžiojo universiteta

KATP kanalų aktyvatorių poveikis širdies mitochondrijų membranų laidumui kalio jonams, protonams ir adp acidozės metu

The inhibition of ATP-ase or the impairment of ADP/ATP transport is suggested to be responsible for the cardioprotective effects of KATP channel openers. In this study, we investigated the ability of KATP channel openers to affect K+ and H+ flux to the matrix of rat heart mitochondria as well as permeability of mitochondrial membranes for ADP under mildly acidic (pH 6.8) conditions. K+ and H+ flux to the mitochondrial matrix was registered spectrophotometrically as the swelling of non-respiring mitochondria at 540 nm in the KNO3 and NH4NO3 medium. The apparent KM for ADP of mitochondria was estimated from the least-squares fit to the Michaelis–Menten equation. The results showed that the KATP channel openers diazoxide and pinacidil could activate potassium ion and proton flux to the mitochondrial matrix both under normal (pH 7.4) and mildly acidic (pH 6.8) conditions. Mild acidosis increased the apparent KM for ADP of mitochondria two times (up to 60.6 ± 3.4 mM) as compared to control (33.0 ± 3.2 mM). The KATP channel opener diazoxide (100 mM) increased the apparent KM for ADP by 40% under control and by 30% under mildly acidic conditions. Our results suggest that KATP channel openers could suppress the ADP/ATP exchange during ischemia and thus promote preservation of ATP in cardiomyocytes

Relevance of fatty acid oxidation in regulation of the outer mitochondrial membrane permeability for ADP

AbstractThe present study on saponin-treated rat heart muscle fibers has revealed a new function of the fatty acid oxidation system in the regulation of the outer mitochondrial membrane (OMM) permeability for ADP. It is found that oxidation of palmitoyl-CoA+carnitine, palmitoyl-L-carnitine and octanoyl-L-carnitine (alone or in combination with pyruvate+malate) dramatically decreased a very high value of apparent Km of oxidative phosphorylation for ADP. Octanoyl-D-carnitine, as well as palmitate, palmitoyl-CoA, and palmitoyl-L-carnitine were not effective in this respect, when their oxidation was prevented by the absence of necessary cofactors or blocked with rotenone. Our data suggest that oxidation, but not transport of fatty acids into mitochondria, induces an increase in the OMM permeability for ADP

Calcium effect on oxidative phosphorylation in rat heart mitochondria

Bibliogr.: 18 pavadKauno medicinos universiteto Biomedicininių tyrimų instituta