C.F. Peng

Abnormal mitochondrial oxidative phosphorylation of ischemic myocardium reversed by Ca2+-chelating agents.

Mitochondria isolated from ischemic and ischemic-reperfused myocardium have been shown to have a defect in electron transport and in energy-linked 45 Ca 2+ uptake. In this study, the influence of Ca 2+ on the efficiency of oxidative phosphorylation by mitochondria isolated from ischemic and ischemic-reperfused myocardium was studied by directly measuring ATP production in the presence and absence of Ca 2+ -chelating agent—EDTA and EGTA. Results demonstrate the following. (a) Mitochondria isolated from ischemic myocardium have a low rate of ATP production, reduced ATP/O ratios and lower net ATP production. These functions are improved by EDTA. (2) Mitochondria from ischemic-reperfused myocardium are totally incapable of phosphorylating ADP in the absence of Ca-chelating agents. Addition of EDTA or EGTA either to the isolation medium or to the incubation medium restores the ability of these mitochondria to phosophorylate all added ADP, although the rate of this phosphorylation remained very slow. (3) The Ca 2+ content of mitochondria from ischemic-reperfused myocardium was higher than the Ca 2+ levels of mitochondria from either normal or ischemic myocardium. These results suggest that phosphorylation of ADP by mitochondria from ischemic and ischemic-reperfused myocardium is inhibited by endogeneous ionic Ca 2+ and that this inhibition can be partially reversed by the addition of Ca 2+ -chelating agents.

Improvement of mitochondrial energy production in ischemic myocardium by in vivo infusion of ruthenium red.

Reperfusion of acutely ischemic myocardium results in deficient energy production and abnormal Ca2+ deposition. This study evaluates mitochondrial energy production in ishemic reperfused myocardium following an in vivo infusion of a Ca2+ antagonist, ruthenium red. Results are summarized as follows: (1) In vivo infusion of ruthenium red increases adenosine diphosphate-induced respiration threefold and adenosine triphosphate (ATP) production fivefold compared with those mitochondria derived from myocardium which had been occluded 2 hr and reperfused 2 hr without ruthenium red. (2) Infusion of ruthenium red improves state 3 respiration and ATP production to nearly normal levels by mitochondria isolated from myocardium which had been occluded 30 min and reperfused 2 hr. However, mitochondrial respiration and ATP production from nonischemic myocardium are not altered by in vivo ruthenium red infusion. (3) Ruthenium red infusion decreases both tissue and mitochondrial Ca2+ content in ischemic-reperfused myocardium. (4) The partial improvement in energy production in ischemic-reperfused myocardium by ruthenium red is probably related to a decrease in intracellular Ca2+ concentration.

Effects of adenine nucleotide translocase inhibitors on dinitrophenol-induced Ca2+ efflux from pig heart mitochondria

Bongkrekic acid and atractyloside, inhibitors of adenine nucleotide translocase, do not inhibit Ca2+ uptake and H+ production by pig heart mitochondria. However, bongkrekic acid, but not atractyloside, inhibits dinitrophenol-induced Ca2+ efflux and H+ uptake. Conversely, ruthenium red blocks Ca2+ uptake and H+ production but does not prevent dinitrophenol-induced Ca2+ efflux and H+ uptake by mitochondria. These results suggest that mitochondrial Ca2+ uptake and release exist as two independent pathways. The efflux of Ca2+ from mitochondria is mediated by a bongkrekic acid sensitive component which is apparently not identical to the ruthenium red sensitive Ca2+ uptake carrier.

Evaluation of biochemical functions and ventricular performance in regional ischemic-reperfused myocardium by afterload reduction: differential effects of calcium blocking and non-calcium blocking vasodilators☆

The effects of afterload reduction with and without calcium blockade on reperfusion injury were studied in the pig. Reversible occlusion of the left anterior descending coronary artery was performed for 60 minutes followed by 120 minutes of reperfusion. For 15 minutes prior to and throughout reperfusion, treatment was administered with a calcium blocker (nifedipine or verapamil), a metallic organic dye and Ca2+ antagonist (ruthenium red), a vasodilator (nitroprusside), or saline. Biochemical functions, i.e., mitochondrial oxidative phosphorylation, myocardial ATP and Ca2+ content, and sarcoplasmic reticulum Ca2+ uptake were determined. Regional left ventricular wall motion was measured echocardiographically. Nifedipine and ruthenium red improved biochemical indices of ischemic myocardium in part by reducing afterload and thereby reducing oxygen demand and in part by reducing calcium entry into cells and mitochondria. Verapamil in the doses used failed to reduce afterload and demonstrated no salutary effect on biochemical parameters in ischemic myocardium. Nitroprusside reduced afterload, improved mitochondrial ATP production and increased percent wall thickening. Our findings suggest that afterload reduction with and without calcium blockade during the early reperfusion phase improves ischemic myocardium. These changes are predominantly biochemical in nature.

Effects of early reperfusion on the mechanical and biochemical characteristics of ischemic myocardium

Coronary reperfusion of ischemic myocardium may be beneficial but is highly dependent upon occlusion and reperfusion times. To study the effects of early reperfusion on ischemic myocardium, 24 open chest pigs underwent coronary occlusion; one group was occluded for 40 min, and the other was occluded for 30 min followed by 10 min of reperfusion. Left ventricular wall thickness during systole and diastole was determined by ultrasound. Mitochondrial energy production and calcium content were evaluated from ischemic and nonischemic areas. Results showed: There was an absence of systolic thickness, a slight decrease of diastolic thickness from baseline, and a decrease in energy production in the ischemic myocardium. Reperfusion resulted in a diverse pattern of systolic and diastolic wall thickness in the ischemic area and a variable Ca2+ accumulation and mitochondrial ATP production. The variability of myocardial Ca2+ accumulation in the ischemic reperfused group correlated inversely with mitochondrial ATP production (r = -0.94) and directly with diastolic wall thickness (r = 0.65). Similarly, calcium accumulation, ATP production, and diastolic wall thickness correlated with mean blood pressure during reperfusion. These results suggest that many factors including individual characteristics of the animal and experimental conditions such as the level of blood pressure and the degree of calcium accumulation may determine outcome of reperfusion even in as brief a period as 10 min.