Calcium Paradox Injury Research Articles

Calculation of the Reversal Potential of the Na+/Ca++ Exchanger Through the Time Course of the Calcium Paradox: A Model Study

The mode of action of the Na/Ca exchanger was calculated during calcium paradox injury. Several different conditions were assumed and the resulting reversal potential was calculated continuously according to the following equation: E_{Na-Ca} = 3*E_{Na}-2*E_{Ca}. The variables were The intracellular Na+ and Ca++ concentrations, and the membrane potential. In the calculations, various combinations of the variable parameters were selected to simulate the most actual conditions during a Ca-Paradox experiment. The possible role of the Na/Ca exchanger in the ethiopathogenesis of the Ca-Paradox injury, or rather whether the exchanger could be involved in the production of the Ca overload observed in reperfused hearts, is investigated. At rest the driving force indicates a net extrution of calcium ions via the Na/Ca exchanger. The exchanger is said to be in the ÒexitÕ mode. As the cell depolarizes, the membrane potential approaches the reversal potential for the exchanger. When the membrane potential is equal to the reversal potential, the exchanger does not cause any net counter transport of ions. If the cell depolarizes further, the exchanger brings calcium into the cell from the extracellular space. Hence, the exchanger is said to be in the ÒentryÓ mode. In the calculations, the mode of action of the exchanger was calculated in response to the changes in the participating potentials Em, ENa, ECa. However, in most of the assumed conditions, the exchanger was calculated to be in the exit mode, indicating a removal of calcium rather than an overload. This study points out that theoretically the exchanger alone may not explain the Ca-overload observed in the reperfused hearts in Ca-Paradox experiments.

Circulatory models in assessment of cardiac enzyme release in dogs.

Cardiac ischemia causes interstitial leakage of cellular enzymes followed by release of these enzymes into plasma. Quantitative interpretation of these data requires a specific circulatory model, and the performance of such models was investigated. Plasma activities of cardiac enzymes were measured for increasingly abrupt forms of ischemic heart injury in the dog: 1) permanent ligation of the left anterior descending coronary artery (LAD); 2) reperfusion after 2 h of ligation of the LAD; and 3) calcium-free perfusion of the LAD during 10 min (calcium-paradox injury). Release into plasma of a rapidly (41%/h) and a slowly (2.2%/h) catabolized enzyme was calculated from the plasma activities, using a detailed circulatory model with compartments for heart, plasma, muscle, skin, and viscera. The time course of cellular enzyme leakage into interstitial space in the heart was calculated from release into plasma and a range of reported values for transendothelial permeability. Simplification to one- and two-compartment models introduced, respectively, 10 and 2% error in calculated cumulative release. Considering the other sources of error, this implies adequate performance of the two-compartment model. Protein washout from the heart is strongly influenced by expansion of interstitial protein space with dead myocyte volume and depends on the microheterogeneity of necrotic tissue areas. Accelerated release of enzymes into plasma after reperfusion reflects accelerated cellular leakage rather than enhanced washout.

Production of hydroxyl radicals and their disassociation from myocardial cell injury during calcium paradox

The production of hydroxyl radicals during calcium paradox injury was investigated by measuring the production of 2,5-dihydroxybenzoic acid (2,5-DHBA) from salicylate. Four groups of rats were analyzed. In the first group, isolated hearts were perfused with calcium-free medium for 10 minutes followed by perfusion with medium containing Ca ++ for 10 minutes. In the other groups, 0.25 μM N,N′-diphenyl-1,3-phenylenediamine (DPPD), 80 μM cytochrome c, or 450 U/ml catalase was added. Coronary effluent was analyzed for the presence of 2,5-DHBA, and tissue sections were examined using light microscopy. In the first group, 2,5-DHBA production began during the calcium-free period, peaked tenfold 60–90 sec. into the Ca repletion period, and declined thereafter. The increase in 2,5-DHBA was accompanied by severe cell damage. Cytochrome c reduced 2,5-DHBA production, and catalase almost completely inhibited 2,5-DHBA production, while DPPD had no effect on 2,5-DHBA production. None of the three additives provided any complete morphological protection. The data provide evidence for the production of hydroxyl radicals during calcium-paradox injury, that their production is dependent upon the presence of hydrogen peroxide, and that cell damage in the calcium paradox is not primarily mediated by the extracellular hydroxyl radicals.

Generation of hydroxyl radicals and their role in the calcium paradox injury

Generation of hydroxyl radicals and their role in the calcium paradox injury

Calcium paradox in an in vivo model of multidose cardioplegia and moderate hypothermia: Prevention with diltiazem or trace calcium levels

The production and prevention of calcium paradox injury in myocardium was studied in a canine model of cardiopulmonary bypass with multidose, moderately hypothermic, crystalloid cardioplegic solution. During 4 1/2 hours of global ischemia, three groups of six dogs each received one of three histidine-buffered cardioplegic solutions (500 ml initially and 250 ml every 30 minutes) at 27 degrees C. Group 1 cardioplegic solution was calcium free, group 2 solution contained a trace amount of calcium chloride (70 mumols /L), and group 3 cardioplegic solution was calcium free but contained diltiazem (150 micrograms/kg body weight). Left ventricular function measured as percent control of developed pressure revealed significantly greater (p less than 0.05) recovery in groups 2 and 3. Triphenyltetrazolium chloride staining showed 35% +/- 9% (mean +/- standard error) of heart mass necrosis in group 1 versus 0% and 0.5% +/- 0.4% in groups 2 and 3, respectively (p less than 0.001). Electron microscopy revealed ultrastructural changes characteristic of calcium paradox injury in group 1 myocardium. Calcium paradox injury was produced in an in vivo model of global myocardial ischemia and multidose cardioplegia despite moderate hypothermia and non-coronary collateral flow. The addition of either trace levels of calcium or diltiazem to the cardioplegic solution was effective in preventing this injury.

Ethanol protects the heart against the calcium paradox injury

Rat hearts were depleted of Ca 2+ (<10 −9M) for 10 min, followed by 15 min of Ca 2+-repletion. The calcium paradox injury occurs during Ca 2+-repletion, after a period of calcium depletion. The calcium paradox injury was assessed by percent recovery (hemodynamics, [Ca 2+] i, and energy levels) during Ca 2+-repletion. A decrease in Na + concentration during Ca 2+-depletion did not allow for recovery during Ca 2+-repletion, however 2.5% and 5% ethanol during Ca 2+-depletion allowed for an approximate 50% recovery during Ca 2+-repletion. A combination of ethanol (2.5% or 5%) with a low extracellular Na + concentration (88 mM) allowed for complete recovery. Ethanol prevented a depletion of diastolic [Ca 2+] i during Ca 2+-depletion, and allowed for a return of normal diastolic [Ca 2+] i during Ca 2+-repletion. Ethanol modulates the activity of the Na + Ca 2+ exchanger and protects against the Ca 2+-paradox injury.

Contracture and cell damage in calcium paradox is not caused by lipid peroxidation.

The role of oxygen radicals and lipid peroxidation in calcium-paradox injury in isolated perfused rat hearts was studied by examining the effects of mannitol and (or) allopurinol on this phenomenon. Myocardial changes due to calcium paradox were characterized by contractile failure, a rise in resting tension, and cell damage. These changes were also accompanied by increased lipid peroxidation, as indicated by an increase in malondialdehyde content. Mannitol (an effective quencher of hydroxyl radicals) treatment resulted in a dose-dependent decrease in lipid peroxidation but did not affect other changes due to calcium paradox. Allopurinol (an inhibitor of xanthine oxidase) neither affected lipid peroxidation nor modified any of the structure-function changes due to calcium paradox. These data demonstrate the occurrence of lipid peroxidation which, however, may not be involved in the observed structure-function changes due to calcium paradox. It is also suggested that in this experimental model, xanthine oxidase may not be the inducer of oxygen radicals or of lipid peroxidation.

Role of oxygen free radicals in calcium paradox injury in myocardium

Role of oxygen free radicals in calcium paradox injury in myocardium

Separation of inherent diastolic myocardial fiber tension and coronary vascular erectile contributions to wall stiffness of rabbit hearts damaged by ischemia, hypoxia, calcium paradox and reperfusion

Ischemic myocardial contracture is exacerbated by reperfusion. This study examines the extent to which intensification of contracture by reperfusion is due to metabolic reoxygenation phenomena or hydraulic erectile contributions of coronary perfusion to left ventricular (LV) stiffness. Isolated rabbit hearts, with fluid-filled LV intraventricular baloons, were subjected either to: control aerobic perfusion; 30 or 60 min of global ischemia; 60 min of hypoxia with constant coronary flow; or 10 min of calcium-free perfusion to cause calcium paradox injury. During reperfusion with control perfusate isovolumic LV end diastolic pressure (LVEDP) was measured with constant coronary flow and during transient, 1 min, total global ischemia to measure the contribution of the coronary perfusion to LVEDP. In all injured groups LVEDP was increased compared to control hearts. The decrease in LVEDP during transient ischemia was greater in damaged hearts than in controls, demonstrating a greater contribution of coronary perfusion to LVEDP after injury. Only in the hypoxic hearts did diastolic fiber tension increase upon reperfusion. Inherent diastolic fiber tension decreased during 15 to 60 min of reperfusion in the ischemic and hypoxic injury groups, a trend which was masked by an increasing effect of coronary perfusion on LV chamber stiffness. During the reperfusion period enhancement of the erectile effect was more pronounced at higher preloads. Thus, reperfusion contracture was maintained both by changes in inherent fiber stiffness and by changes in the erectile effect. These contributions changed over time and varied with the type and severity of injury, but after all types of injury the erectile vascular effect made a greater contribution to diastolic chamber stiffness than inherent fiber tension.

The temperature-sensitivity of slow channel calcium blockers in relation to their effect upon the calcium paradox

The isolated perfused rat heart preparation was used to investigate the interrelationship between temperature and the ability of calcium antagonists to reduce protein leakage in the calcium paradox. Exploiting the fact that although the calcium depletion phase of calcium paradox-injury is highly temperature sensitive, the calcium repletion phase, during which time the injury is manifested, is temperature independent. Verapamil (4 mumol l-1) included in a 10 min period of calcium depletion (37 degrees C) and a 20 min period of calcium repletion (37 degrees C) was known to reduce cumulative protein leakage by 22 +/- 3%. With calcium depletion again at 37 degrees C but repletion at 21 degrees C verapamil failed to achieve any reduction in protein leakage despite the fact that leakage in the 21 degrees C control group did not differ significantly from that in the 37 degrees C control group. Temperature-response studies (repletion temperature of 4, 10, 21, 23, 25, 28, 31, 34 and 37 degrees C) revealed an abrupt loss of drug effect below 25 degrees C. Studies with D600 (10 mumol l-1), nifedipine (4 mumol l-1), terodiline (4 mumol l-1) fendiline (20 mumol l-1) and diltiazem (2 mumol l-1) revealed that while all of these drugs reduced protein leakage at 37 degrees C (24 +/- 3%, 31 +/- 2%, 31 +/- 3%, 23 +/- 3% and 29 +/- 3%, respectively), like verapamil they had no effect at 21 degrees C.(ABSTRACT TRUNCATED AT 250 WORDS)

Prevention of calcium paradox-related myocardial cell injury with diltiazem, a calcium channel blocking agent

The effect of diltiazem on creatine kinase release and tissue adenosine triphosphate content was investigated during calcium paradox in the isolated perfused rat heart. Creatine kinase loss was minimal during the calcium-free phase, but there was a 100-fold increase in creatine kinase release after reperfusion with normal calcium-containing medium. Diltiazem reduced creatine kinase loss by 35 percent when added to calcium-free medium and by approximately 80 percent when added to both calcium-free and reperfusion media. Adenosine triphosphate content was significantly increased from 2.98 μmol in untreated calcium paradox hearts to 5 μmol/g dry weight in diltiazem-treated hearts. With hyopthermia the calcium paradox injury was completely inhibited if the temperature of calcium-free perfusion was maintained at 15 ° C. Diltiazem appears to exert its protective effect through its ability to prevent the cellular separation and alterations in the gap junctions during calcium deprivation of cells and to limit calcium entry into the cells after reperfusion with calcium-containing medium.