Ruthenium red as a carrier of electrons between external NADH and cytochrome c in rat liver mitochondria

Use of ruthenium red as an inhibitor of mitochondrial Ca(2+) uptake in single rat cardiomyocytes

With the current resurgence of interest in the role of mitochondrial [Ca(2+)] in energy production and cellular Ca(2+) signalling, ruthenium red (RR) is being increasingly used as an inhibitor of mitochondrial Ca(2+) uptake. In the present study, the effects of RR on cell and mitochondrial [Ca(2+)], and on cell contractility were determined in isolated rat ventricular myocytes subjected to adrenergic and electrical stimulation. At low concentrations, 0-1 microM, RR inhibited mitochondrial Ca(2+) uptake but this was a secondary effect due to a reduced total intracellular [Ca(2+)], a conclusion supported by the ability of RR to inhibit cell shortening. 5 microM RR completely inhibited cell contraction, whereas higher concentrations, 10-25 microM, induced spontaneous Ca(2+) oscillations and contractile waves. These results indicate that great care must be taken when using RR in intact cells, and in interpreting any effects as resulting from a primary inhibition of mitochondrial Ca(2+) uptake.

Verapamil directly inhibits aldosterone synthesis by adrenal mitochondria in vitro

The action of verapamil, a calcium channel blocker, on the last step of aldosterone biosynthesis (transformation of 18-hydroxycorticosterone into aldosterone) was studied using duck adrenal mitochondria in the absence of regulatory factors. Results show that 10(-5) M verapamil inhibits the transformation of 18-hydroxycorticosterone into aldosterone by 52.8%. Moreover, our findings show that verapamil induces only a slight inhibition of respiratory capacity without action on respiratory control and does not displace 18-hydroxycorticosterone from cytochrome P450 11 beta which catalyses the reaction. Thus, this study does not explain the mechanism of inhibition induced by verapamil on the last step of aldosterone synthesis but it is of interest to note, for clinical use, that this inhibition is not linked to regulatory factors of aldosterone production. Since primary hyperaldosteronisms are characterized by their independence vis-á-vis regulatory factors, administration of verapamil may be particularly interesting for treatment of primary hyperaldosteronisms.

Cytochrome b reduction by hexaammineruthenium in mitochondria and submitochondrial particles. Evidence for heme b-562 localization at the M-side of the mitochondrial membrane

In the presence of ascorbate, hexaamineruthenium mediates rapid reduction of cytochrome b-562 in submitochondrial particles but not in mitochondria. The reaction is observed in the combined presence of antimycin (or funiculosin) and myxothiazol, which implies direct interaction of Ru(NH3)2+6 with b cytochrome(s). We assume that contrary to previous conclusions (Case and Leigh (1976) Biochem. J., 160, 769-783) redox centre of at least one of the oxidized cytochromes b, most probably of b-562, is exposed to the M-aqueous phase.

Cytochrome c mediates electron transfer between ubiquinol-cytochrome c reductase and cytochrome c oxidase by free diffusion along the surface of the membrane

Ubiquinol oxidase can be reconstituted from ubiquinol-cytochrome c reductase (Complex III) and cytochrome c oxidase (Complex IV) whose endogenous phosphatidylcholine and phosphatidylethanolamine have been replaced by dimyristoylglycerophosphocholine. Phase transition of the lipid has no effect on Complex III and Complex IV activities assayed separately, but ubiquinol oxidase activity rapidly decreases as the temperature is lowered through the phase transition. A spin-labelled yeast cytochrome c derivative has been synthesized. Binding of the cytochrome c to liposomes demonstrates that only cardiolipin is involved under the conditions used for the ubiquinol oxidase experiments. In liposomes consisting of cardiolipin and dimyristoylglycerophosphocholine, e.s.r. (electron-spin-resonance) measurements show that rotational diffusion of cytochrome c is slowed in the gel phase of the latter lipid. We propose that the cytochrome c pool is bound to cardiolipin molecules, whose lateral and rotational diffusion in the bilayer is adequate to account for electron-transport rates.

Characteristics of the active transport of Ca2+ by submitochondrial vesicles

Inner membrane vesicles have been prepared by cholate treatment of rat liver mitoplasts. The vesicles can actively accumulate Ca2+ in the absence or presence of inorganic phosphate. The uptake is inhibited by ruthenium red and uncouplers of oxidative phosphorylation. Like in intact mitochondria the driving force for the uptake reaction seems to be the negative inside membrane potential generated during the oxidation of substrates. The level of antimycin-A-sensitive reduction of ferricyanide by succinate indicates that the cholate inner membrane vesicles are about 70% right side out. Using cytochrome-c-extracted inner membrane vesicles it can be shown that only those which have the same right-side-out polarity as intact mitochondria can actively accumulate Ca2+.