This study shows that the hydrophobic cation octylguanidine protects against myocardial damage induced by ischemia-reperfusion. The protective effect of the amine was analyzed after 5 min of coronary occlusion followed by 5 min reperfusion in rat hearts. ECG tracings from rats treated with an i.v., injection of 5 mg/kg of octylguanidine showed a total absence of post-reperfusion arrhythmias, conversely to what was observed in untreated rats. The histological images showed that myocardium fibers from treated rats were in good shape and retained their striae, also there was absence of edema. Furthermore, the accumulation of 201Tl in hearts from these rats indicated that the tissue did not suffer disruption or impairment in membrane functions. The above correlated with the fact that mitochondria isolated from the ventricular free wall from treated rats preserved their ability to synthesize ATP. We propose that the protective effect of octylguanidine might be due to its documented inhibitory action on the opening of mitochondrial non-specific pores, a mechanism which is associated in heart injury as induced by reperfusion.

No abstract

The purpose of this work was to assess the effect of oligomycin on the mitochondrial membrane permeability transition. The antibiotic was found to strengthen cyclosporin A (CSA)-induced protection of non-specific permeability, which is triggered by a matrix Ca2+ load in the absence of ADP. Oligomycin also reinforced the protective effect of CSA on carboxyatractyloside-induced pore opening in the absence of ADP, but failed to do so in mitochondria incubated under anaerobic conditions or after addition of CCCP. Analyzing the efflux of matrix Ca2+, we found that mitochondrial swelling and the collapse of the transmembrane electric gradient coincided with membrane leakage. The effects of the antibiotic were observed in phosphate-containing media but not in the presence of acetate. Furthermore, N-ethylmaleimide hindered the protective effect of oligomycin-CSA. In addition, the matrix phosphate concentration increased concurrently with a diminution in the matrix-free fraction of Ca2+. We concluded that oligomycin increases phosphate uptake by stimulating the phosphate-/OH- exchange reaction.

No abstract

The mitochondrial calcium uniporter behaves as a cooperative mechanism, where the velocity is dependent on [Ca2+]ex. Transport kinetics follows a sigmoidal behavior with a Hill coefficient near 2.0, indicating the binding of at least two calcium molecules. Calcium transport in mitochondria is dependent on a negative inner membrane potential and is inhibited by policationic ruthenium compounds. In this study, calcium uptake activity was reconstituted into cytochrome oxidase vesicles by incorporating solubilized mitochondrial proteins. Calcium accumulation plotted against increasing Ca2+ concentrations followed a sigmoidal behavior with a Hill coefficient of 1.53. The uptake was sensitive to ruthenium policationic inhibitors, e.g. ruthenium red and Ru360. After mitochondrial proteins were separated by preparative isoelectrofocusing and incorporated into cytochrome oxidase vesicles, two peaks of calcium uptake activity were recovered. One of the activities was inhibited by Ru360, while the second activity was insensitive to Ru360 and was associated with proteins focused at very acidic isoelectric points. By using a thiol-group crosslinker and radiolabeled Ru360, we proposed a scheme of partial dissociation of the uniporter inhibitor-binding subunit under acidic conditions.