Karl D. Straub

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.

The Role of Hydrogen Sulfide in Evolution and the Evolution of Hydrogen Sulfide in Metabolism and Signaling

The chemical versatility of sulfur and its abundance in the prebiotic Earth as reduced sulfide (H2S) implicate this molecule in the origin of life 3.8 billion years ago and also as a major source of energy in the first seven-eighths of evolution. The tremendous increase in ambient oxygen ∼ 600 million years ago brought an end to H2S as an energy source, and H2S-dependent animals either became extinct, retreated to isolated sulfide niches, or adapted. The first 3 billion years of molecular tinkering were not lost, however, and much of this biochemical armamentarium easily adapted to an oxic environment where it contributes to metabolism and signaling even in humans. This review examines the role of H2S in evolution and the evolution of H2S metabolism and signaling.

Catalase as a sulfide-sulfur oxido-reductase: An ancient (and modern?) regulator of reactive sulfur species (RSS)

Catalase is well-known as an antioxidant dismutating H2O2 to O2 and H2O. However, catalases evolved when metabolism was largely sulfur-based, long before O2 and reactive oxygen species (ROS) became abundant, suggesting catalase metabolizes reactive sulfide species (RSS). Here we examine catalase metabolism of H2Sn, the sulfur analog of H2O2, hydrogen sulfide (H2S) and other sulfur-bearing molecules using H2S-specific amperometric electrodes and fluorophores to measure polysulfides (H2Sn; SSP4) and ROS (dichlorofluorescein, DCF). Catalase eliminated H2Sn, but did not anaerobically generate H2S, the expected product of dismutation. Instead, catalase concentration- and oxygen-dependently metabolized H2S and in so doing acted as a sulfide oxidase with a P50 of 20 mmHg. H2O2 had little effect on catalase-mediated H2S metabolism but in the presence of the catalase inhibitor, sodium azide (Az), H2O2 rapidly and efficiently expedited H2S metabolism in both normoxia and hypoxia suggesting H2O2 is an effective electron acceptor in this reaction. Unexpectedly, catalase concentration-dependently generated H2S from dithiothreitol (DTT) in both normoxia and hypoxia, concomitantly oxidizing H2S in the presence of O2. H2S production from DTT was inhibited by carbon monoxide and augmented by NADPH suggesting that catalase heme-iron is the catalytic site and that NADPH provides reducing equivalents. Catalase also generated H2S from garlic oil, diallyltrisulfide, thioredoxin and sulfur dioxide, but not from sulfite, metabisulfite, carbonyl sulfide, cysteine, cystine, glutathione or oxidized glutathione. Oxidase activity was also present in catalase from Aspergillus niger. These results show that catalase can act as either a sulfide oxidase or sulfur reductase and they suggest that these activities likely played a prominent role in sulfur metabolism during evolution and may continue do so in modern cells as well. This also appears to be the first observation of catalase reductase activity independent of peroxide dismutation.

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.

Effects of reperfusion on myocardial wall thickness, oxidative phosphorylation, and Ca2+ metabolism following total and partial myocardial ischemia

Coronary artery reperfusion following acute myocardial ischemia may salvage ischemic jeopardized cells. We studied the effects of early brief reperfusion on totally ischemic and on partially ischemic myocardium of open-chest pigs. In 10 animals, coronary flow was reduced to 0% for 30 minutes and was followed by 10 minutes reperfusion (group A). In another 10 animals, coronary flow was reduced to 25% of the baseline value for 30 minutes followed by 10 minutes of reperfusion (group B). In another eight animals coronary flow was reduced to 25% of the baseline value for 60 minutes and followed by 10 minutes of reperfusion (group C). Results showed that a brief 10-minute period of reperfusion of ischemic myocardium after total occlusion caused abnormal diastolic wall thickening with only partial return of systolic wall thickening. However, reperfusion of ischemic myocardium after partial occlusion, whether 30 or 60 minutes, caused little diastolic wall thickening and a partial return of systolic thickening. A marked elevation of myocardial Ca2+, a decrease in mitochondrial adenosine triphosphate (ATP) production and cellular ATP concentration, and a reduction in the rate of Ca2+ uptake by sarcoplasmic reticulum vesicles occurred in the totally ischemic myocardium but not in the partially ischemic myocardium. These results demonstrate that reperfusion of ischemic myocardium after 1 hour of coronary flow reduction to 25% of baseline is less damaging than reperfusion after a 30-minute total coronary occlusion, and suggest that preexisting states affecting coronary flow need to be evaluated in assessing the outcome of reperfusion.

The adverse effect of systemic hypertension following myocardial reperfusion

Transient myocardial ischemia in postoperative hypertension is relatively common with coronary artery bypass surgery. This study examines the effect of hypertension during reperfusion of transiently ischemic myocardium. The animal model was open chest pigs with myocardial ischemia induced by the occlusion of the left anterior descending coronary artery for 30 min followed by 2 hr of reperfusion. A normotensive control group was compared with animals rendered hypertensive with phenylephrine during the ischemic and reperfusion times. In the hypertensive group, systolic blood pressure was raised from 106 to 161 mm Hg and peripheral vascular resistance from normal to 3600 dyn-sec-cm-5. Regional left ventricular wall thickness, mitochondrial function, sarcoplasmic reticulum Ca2+ uptake, tissue calcium, water content, and hemorrhage were evaluated. Compared to controls the hypertensive group had (1) loss of systolic wall thickening with increased diastolic wall thickness in the reperfused zone, (2) intramyocardial hemorrhage in the area of reperfusion, (3) significant impairment of oxidative phosphorylation by mitochondria isolated from the reperfused zone, (4) a marked reduction in the rate of Ca2+ uptake by sarcoplasmic reticulum vesicles, and (5) an increase in ischemic tissue calcium. Thus, hypertension associated with revascularization of acutely ischemic myocardium may accentuate myocardial damage.

Wall motion and metabolic changes after coronary occlusion and reperfusion.

Abstract Experiments were conducted in open-chest pigs in which experimental myocardial ischemia was produced. Two groups of animals were evaluated: (1) those with short episodes of coronary occlusion and reperfusion, and (2) those with an initially longer period of occlusion (equal to the sum of the short multiple occlusions) and reperfusion. Indices of myocardial wall motion as determined by echocardiogram, of energy production as measured by mitochondrial oxidative phosphorylation, and of cellular membrane integrity as measured by calcium uptake by sarcoplasmic reticulum vesicles and calcium content of tissue and mitochondria were obtained. Our observation revealed better myocardial preservation in the group with brief periods of occlusion and reperfusion than those with a sustained period of ischemia followed by reperfusion. The concept that myocardium is less well preserved due to reperfusion damage by intermittent aortic cross-clamping or intermittent coronary perfusion during open heart surgery compared to uninterrupted cardiac arrest needs to be reexamined in light of the data presented and investigated in the hypothermic, cardioplegia model.

Digoxin uptake into peripheral autonomic cardiac nerves: Possible mechanism of digitalis-induced antiarrhythmic and toxic electrophysiologic actions

It is generally accepted that certain cardiac rhythm disturbances are due to imbalances between the sympathetic and parasympathetic nervous systems. We have provided evidence that digoxin is concentrated in the peripheral nervous system of the heart as well as in the central nervous system. Previous findings have indicated that cardiac glycosides may directly or indirectly affect autonomic neurotransmitters. Therefore the uptake of digoxin into the peripheral cardiac nervous system may play an important role in both the antiarrhythmic and toxic electrophysiologic actions of digoxin.

Comparison of the canine tissue distribution of digoxin after acute and chronic administration implications for digitalis therapy

Digoxin is often used as an antiarrhythmic and inotropic agent. It produces significant neuroexcitatory responses that influence both its therapeutic and toxic effects. Patients receiving digoxin can be separated into 2 groups: those who receive it acutely and those who receive it chronically. The therapeutic and toxic responses to digoxin vary between these groups. The neural tissue distribution of digoxin was compared in dogs after both acute and chronic injections. Acute administration of digitalis in this study was associated with preferential uptake of digoxin into peripheral sympathetic nerves. Chronic administration was associated with continued selective uptake into the central nervous system despite decreasing serum levels. Therefore, acute (experimental or suicidal) or chronic (maintenance) digoxin administration produces different neural responses. The peripheral sympathetic nervous system will be the primary area of interaction with acute digoxin administration and the central nervous system will have a greater involvement with chronic digoxin administration. Our results indicate that the uptake of digoxin into the peripheral nervous system and central nervous system depends upon the duration of digoxin administration. The time course of digoxin accumulation influences both its therapeutic and toxic actions.