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Studies on oxygen and volume restriction in cultured heart cells: The transition from reversible to irreversible damage
j Mol Cell Cardiol 18 (Supplement 3) (1986) DAZOXIBEN PROTECTSADENINE NUCLEOTIDELOSS WITHOUT IMPROVING SEGMENTDYSFUNCTION IN THE "STUNNED" MYOCARDIUM. G.M. Pieper, N.E. Farber, G.J. Gross. Dept. Pharmacol. and Toxicol., Medical College of Wisconsin, Milwaukee, WI 53226 U.S.A. Inhibition of thromboxane synthesis has been shown to reduce ventricular f i b r i l l a t i o n during post-ischemic reperfusion. This study tested whether inhibition by dazoxiben (5 mg/kg i . v . ) could also reverse regional contractile dysfunction and protect against adenine nucleotide (AN) loss in the "stunned" ntyocardium. Hearts from anesthetized dogs were "stunned" by 15 min of l e f t anterior descending artery occlusion followed by 3 hr of reperfusion. Segmentshortening (% SS) and ~qocardial blood flow (MBF) were measured by sonimicrometry and the microsphere technique. Local venous blood was taken for thromboxaneand prostaglandin assay. Biopsies from reperfused and nonischemic areas were taken at 3 hr for AN analysis. % SS in the ischemic zone was severely depressed during ischemia (with passive systolic bulging) in both control and dazoxiben-treated hearts. Deprivation of MBF during ischemia was similar in both groups. During reperfusion, % SS recovered only p a r t i a l l y and was not significantly improved by dazoxiben. Dazoxiben augmentedpeak PGI2 production (18% vs. I12%) following reperfusion and attenuated the decline in endocardial ATP (69 + 5% vs. 92 + 9% normalized to the nonischemic zone) and total AN. Thus, the throm~oxane synthesis i n h i b i t o r , dazoxiben, does not significantly improve post-ischemic segment dysfunction despite salient effects in preserving ATP.
MEMBRANE DEFECTS DURING THE DEVELOPMENT OF DIABETIC CARDIOMYOPATHY. G.N. Pierce, N.S. Dhalla. Departmentof Physiology, University of Manitoba, Winnipeg, Canada. Extensive evidence demonstrates the heart to be in a pathophysiological condition during diabetes. The mechanism responsible for the cardiac dysfunction during diabetes may involve an alteration in the i n t e g r i t y of the subcellular membranesystems: the mitochondria, sarcoplasmic reticulum (SR) and sarcolemma (SL). Isolated SR vesicles from diabetic rat hearts exhibit a significantly depressed capacity to transport Ca2+ in comparison to control. This lesion appears to be due in part to a depression in Ca2+ stimulated ATPase a c t i v i t y . Mitochondria isolated from diabetic rat hearts exhibit lower oxidative phosphor~lation capacity and Mg2+-ATPase a c t i v i t y than control preparations. Mitochondrial CaZ+ uptake is also depressed in diabetic preparations in comparison to contol. SL vesicles from the diabetic myocardiumexhibit a significantly lower capacity to bind Ca2+ than control vesicles. Ouabain-sensitive Na+, K+-ATPase and K+-pNPPase a c t i v i t i e s are also reduced in the diabetic rat heart SL. These SL alterations may be explained by changes in membranecomposition. The results present a composite picture of generalized depression in membranefunction, particularly with respect to the Ca2+ buffering capacity of the c e l l . We hypothesize that an alteration in c e l l u l a r ionic homeostasis, particularly Caz+, may be intimately involved in the cardiac pathology during diabetes, and that membranedefects play an important role in i t s genesis.
STUDIES ON OXYGEN AND VOLUME RESTRICTION IN CULTURED HEART CELLS: THE TRANSITION FROM REVERSIBLE TO IRREVERSIBLE DAMAGE. A. Pinson, R. Vemuri, J.W. de Jong , Laborato{y for Myocardial Research, Hebrew University-Hadassah Medical School, Israel, Cardiochemical Laboratory, Thorax Center, Erasmus University, Rotterdam, The Netherlands. Cardiac ischaemia has been simulated in a cultured heart cell system by the adoption of appropriate conditions. Cytosolic enzymes were released into the medium shortly after the onset of anoxic injury, while there was a lag period of about two hours before lysosomal enzyme release. The latter was accompanied by a dramatic decrease in the cellular energy charge and an accelerated rate of protein degradation, indicating uncontrolled activity of lysosomal hydrolases. Reoxygenation and reperfusion halted enzyme release - giving rise to complete restoration of cellular energy charge and beating function within 30 to 60 rain if performed before the onset of lysosomal enzyme release (i.e., during the first two hours), and to delayed and only incomplete restoration if carried out after more than two hours. These results indicate that cytosolic enzyme release occurs during a still reversible phase of cell damage, whereas lysosomal enzyme release takes place during the irreversible phase, as evidenced by the continuation of enzyme release upon reoxygenation, and the "collapse" of various structures within the cell. This brings about acceleration of degradative processes, and incomplete restoration of cellular functions over a longer time period, upon reperfusion and reoxygenation.
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MEMBRANE DEFECTS DURING THE DEVELOPMENT OF DIABETIC CARDIOMYOPATHY. G.N. Pierce, N.S. Dhalla. Departmentof Physiology, University of Manitoba, Winnipeg, Canada. Extensive evidence demonstrates the heart to be in a pathophysiological condition during diabetes. The mechanism responsible for the cardiac dysfunction during diabetes may involve an alteration in the i n t e g r i t y of the subcellular membranesystems: the mitochondria, sarcoplasmic reticulum (SR) and sarcolemma (SL). Isolated SR vesicles from diabetic rat hearts exhibit a significantly depressed capacity to transport Ca2+ in comparison to control. This lesion appears to be due in part to a depression in Ca2+ stimulated ATPase a c t i v i t y . Mitochondria isolated from diabetic rat hearts exhibit lower oxidative phosphor~lation capacity and Mg2+-ATPase a c t i v i t y than control preparations. Mitochondrial CaZ+ uptake is also depressed in diabetic preparations in comparison to contol. SL vesicles from the diabetic myocardiumexhibit a significantly lower capacity to bind Ca2+ than control vesicles. Ouabain-sensitive Na+, K+-ATPase and K+-pNPPase a c t i v i t i e s are also reduced in the diabetic rat heart SL. These SL alterations may be explained by changes in membranecomposition. The results present a composite picture of generalized depression in membranefunction, particularly with respect to the Ca2+ buffering capacity of the c e l l . We hypothesize that an alteration in c e l l u l a r ionic homeostasis, particularly Caz+, may be intimately involved in the cardiac pathology during diabetes, and that membranedefects play an important role in i t s genesis.
STUDIES ON OXYGEN AND VOLUME RESTRICTION IN CULTURED HEART CELLS: THE TRANSITION FROM REVERSIBLE TO IRREVERSIBLE DAMAGE. A. Pinson, R. Vemuri, J.W. de Jong , Laborato{y for Myocardial Research, Hebrew University-Hadassah Medical School, Israel, Cardiochemical Laboratory, Thorax Center, Erasmus University, Rotterdam, The Netherlands. Cardiac ischaemia has been simulated in a cultured heart cell system by the adoption of appropriate conditions. Cytosolic enzymes were released into the medium shortly after the onset of anoxic injury, while there was a lag period of about two hours before lysosomal enzyme release. The latter was accompanied by a dramatic decrease in the cellular energy charge and an accelerated rate of protein degradation, indicating uncontrolled activity of lysosomal hydrolases. Reoxygenation and reperfusion halted enzyme release - giving rise to complete restoration of cellular energy charge and beating function within 30 to 60 rain if performed before the onset of lysosomal enzyme release (i.e., during the first two hours), and to delayed and only incomplete restoration if carried out after more than two hours. These results indicate that cytosolic enzyme release occurs during a still reversible phase of cell damage, whereas lysosomal enzyme release takes place during the irreversible phase, as evidenced by the continuation of enzyme release upon reoxygenation, and the "collapse" of various structures within the cell. This brings about acceleration of degradative processes, and incomplete restoration of cellular functions over a longer time period, upon reperfusion and reoxygenation.
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