Mechanisms of cardiodepression by an Na+–H+ exchange inhibitor methyl-N-isobutyl amiloride (MIA) on the heart: lack of beneficial effects in ischemia–reperfusion injuryThis paper is one of a selection of papers published in this Special Issue, entitled Young Investigators' Forum.

2007 ◽  
Vol 85 (1) ◽  
pp. 67-78 ◽  
Author(s):  
Harjot K. Saini ◽  
Vijayan Elimban ◽  
A. Tanju Ozcelikay ◽  
Naranjan S. Dhalla
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Cardiac Function ◽  
Atpase Activity ◽  
Direct Effect ◽  
Positive Inotropic Effect ◽  
Ischemia Reperfusion ◽  
Negative Inotropic Effect ◽  
Inotropic Effect ◽  
Beneficial Effects ◽  
Intracellular Ca

Although Na+–H+ exchange (NHE) inhibitors such as methyl-N-isobutyl amiloride (MIA) are known to depress the cardiac function, the mechanisms of their negative inotropic effect are not completely understood. In this study, isolated rat hearts were perfused with MIA to study its action on cardiac performance, whereas isolated subcellular organelles such as sarcolemma, myofibrils, sarcoplasmic reticulum, and mitochondria were treated with MIA to determine its effect on their function. The effect of MIA on intracellular Ca2+ mobilization was examined in fura-2-AM-loaded cardiomyocytes. MIA was observed to depress cardiac function in a concentration-dependent manner in HCO3–-free buffer. On the other hand, MIA had an initial positive inotropic effect followed by a negative inotropic effect in HCO3–-containing buffer. MIA increased the basal concentration of intracellular Ca2+ ([Ca2+]i) and augmented the KCl-mediated increase in [Ca2+]i. MIA did not show any direct effect on myofibrils, sarcolemma, and sarcoplasmic reticulum ATPase activities; however, this agent was found to decrease the intracellular pH, which reduced the myofibrils Ca2+-stimulated ATPase activity. MIA also increased Ca2+ uptake by mitochondria without having any direct effect on sarcoplasmic reticulum Ca2+ uptake. In addition, MIA did not protect the hearts subjected to mild Ca2+ paradox as well as ischemia–reperfusion-mediated injury. These results suggest that the increase in [Ca2+]i in cardiomyocytes may be responsible for the initial positive inotropic effect of MIA, but its negative inotropic action may be due to mitochondrial Ca2+ overloading as well as indirect depression of myofibrillar Ca2+ ATPase activity. Thus the accumulation of [H+]i as well as occurrence of intracellular and mitochondrial Ca2+ overload may explain the lack of beneficial effects of MIA in preventing the ischemia–reperfusion-induced myocardial injury.

scholarly journals Attenuation of extracellular ATP response in cardiomyocytes isolated from hearts subjected to ischemia-reperfusion

2005 ◽  
Vol 289 (2) ◽  
pp. H614-H623 ◽  
Author(s):  
Harjot K. Saini ◽  
Vijayan Elimban ◽  
Naranjan S. Dhalla
Keyword(s):  
Cardiac Function ◽  
Positive Inotropic Effect ◽  
Ischemia Reperfusion ◽  
Cardiac Contractility ◽  
Extracellular Atp ◽  
Binding Characteristics ◽  
Rat Hearts ◽  
The Status ◽  
Intracellular Ca ◽  
Isolated Rat

Extracellular ATP is known to augment cardiac contractility by increasing intracellular Ca2+ concentration ([Ca2+]i) in cardiomyocytes; however, the status of ATP-mediated Ca2+ mobilization in hearts undergoing ischemia-reperfusion (I/R) has not been examined previously. In this study, therefore, isolated rat hearts were subjected to 10–30 min of global ischemia and 30 min of reperfusion, and the effect of extracellular ATP on [Ca2+]i was measured in purified cardiomyocytes by fura-2 microfluorometry. Reperfusion for 30 min of 20-min ischemic hearts, unlike 10-min ischemic hearts, revealed a partial depression in cardiac function and ATP-induced increase in [Ca2+]i; no changes in basal [Ca2+]i were evident in 10- or 20-min I/R preparations. On the other hand, reperfusion of 30-min ischemic hearts for 5, 15, or 30 min showed a marked depression in both cardiac function and ATP-induced increase in [Ca2+]i and a dramatic increase in basal [Ca2+]i. The positive inotropic effect of extracellular ATP was attenuated, and the maximal binding characteristics of 35S-labeled adenosine 5′-[γ-thio]triphosphate with crude membranes from hearts undergoing I/R was decreased. ATP-induced increase in [Ca2+]i in cardiomyocytes was depressed by verapamil and Cibacron Blue in both control and I/R hearts; however, this response in I/R hearts, unlike control hearts, was not affected by ryanodine. I/R-induced alterations in cardiac function and ATP-induced increase in [Ca2+]i were attenuated by treatment with an antioxidant mixture and by ischemic preconditioning. The observed changes due to I/R were simulated in hearts perfused with H2O2. The results suggest an impairment of extracellular ATP-induced Ca2+ mobilization in I/R hearts, and this defect appears to be mediated through oxidative stress.

Ischemia–reperfusion-induced changes in sarcolemmal Na+/K+-ATPase are due to the activation of calpain in the heartThis article is one of a selection of papers published in a Special Issue on Oxidative Stress in Health and Disease.

2010 ◽  
Vol 88 (3) ◽  
pp. 388-397 ◽  
Author(s):  
Raja B. Singh ◽  
Naranjan S. Dhalla
Keyword(s):  
Oxidative Stress ◽  
Cardiac Function ◽  
Atpase Activity ◽  
Protein Content ◽  
Ischemia Reperfusion ◽  
Specific Inhibitor ◽  
Calpain Activity ◽  
Rat Hearts ◽  
Intracellular Ca ◽  
Calpain Inhibitors

Depression in cardiac performance due to ischemia–reperfusion (I/R) injury is associated with the development of oxidative stress and decreased sarcolemmal (SL) Na+/K+-ATPase activity. Since both I/R and oxidative stress have been reported to promote the occurrence of intracellular Ca2+ overload and activate proteases such as calpain, this study was undertaken to investigate whether the activation of calpain in I/R hearts is associated with alterations in the SL Na+/K+-ATPase activity and its isoform content. For this purpose, isolated rat hearts treated with and without 2 different calpain inhibitors (leupeptin and MDL28170) were subjected to 30 min ischemia followed by 60 min of reperfusion, and the cardiac function, SL Na+/K+-ATPase activity, Na+/K+-ATPase isoform protein content, and calpain activity were measured. The I/R-induced depressions in cardiac function, Na+/K+-ATPase activity, and protein content of Na+/K+-ATPase isoforms were associated with an increase in calpain activity , but were prevented by treatment of hearts with leupeptin. Incubation of SL membranes with calpain decreased the Na+/K+-ATPase activity and protein content of its isoforms; these changes were also attenuated by leupeptin. The I/R-induced alterations in cardiac function and the activity of SL Na+/K+-ATPase and calpain were Ca2+-dependent and were prevented by MDL28170, a specific inhibitor of calpain. The I/R-induced translocation of calpain isoforms (I and II) from the cytosol to SL and the changes in distribution of calpastatin were also attenuated by treatment with calpain inhibitors. These results suggest that the depression in cardiac function and SL Na+/K+-ATPase activity in I/R hearts may be due to changes in the activity and translocation of calpain.

Modification of alterations in cardiac function and sarcoplasmic reticulum by vanadate in ischemic-reperfused rat hearts

2005 ◽  
Vol 99 (3) ◽  
pp. 999-1005 ◽  
Author(s):  
Satoshi Takeda ◽  
Seibu Mochizuki ◽  
Harjot K. Saini ◽  
Vijayan Elimban ◽  
Naranjan S. Dhalla
Keyword(s):  
Superoxide Dismutase ◽  
Sarcoplasmic Reticulum ◽  
Cardiac Function ◽  
Diastolic Pressure ◽  
Ischemia Reperfusion ◽  
Cardiac Performance ◽  
Sr Protein ◽  
Release Channel ◽  
Beneficial Effects ◽  
Rat Hearts

To study the cardioprotective effects of vanadate on ischemia-reperfusion (I/R) injury, isolated rat hearts perfused at constant flow were subjected to global ischemia for 30 min followed by reperfusion for 30 min. In this experimental model, I/R markedly decreased ventricular developed pressure and increased end-diastolic pressure. Pretreatment of hearts with 4 μM vanadate attenuated I/R-induced cardiac dysfunction. The reduction in sarcoplasmic reticulum (SR) Ca2+ uptake and Ca2+ release, as well as SR protein contents for Ca2+-pump ATPase and Ca2+-release channel, was also prevented by vanadate. Pretreatment of hearts with an antioxidant mixture containing superoxide dismutase + catalase exerted effects similar to those of vanadate in I/R hearts. Postischemic treatment of hearts with vanadate or superoxide dismutase + catalase also had beneficial effects on I/R-induced changes in cardiac performance and SR function. Alterations in cardiac function and SR Ca2+ transport due to an oxyradical-generating system (xanthine + xanthine oxidase) or an oxidant (H2O2) were attenuated by treatment with vanadate. These results suggest that vanadate may exert beneficial effects on cardiac performance and SR function in I/R hearts because of its antioxidant action.

Role of dual-site phospholamban phosphorylation in intermittent hypoxia-induced cardioprotection against ischemia-reperfusion injury

2005 ◽  
Vol 288 (6) ◽  
pp. H2594-H2602 ◽  
Author(s):  
Yan Xie ◽  
Yi Zhu ◽  
Wei-Zhong Zhu ◽  
Le Chen ◽  
Zhao-Nian Zhou ◽  
...  
Keyword(s):  
Atpase Activity ◽  
Ischemia Reperfusion Injury ◽  
Ischemia Reperfusion ◽  
Cardiac Sarcoplasmic Reticulum ◽  
Beneficial Effects ◽  
Protein Levels ◽  
Rat Hearts ◽  
Intracellular Ca ◽  
Contractile Recovery ◽  
Dual Site

Cardioprotection by intermittent high-altitude (IHA) hypoxia against ischemia-reperfusion (I/R) injury is associated with Ca2+ overload reduction. Phospholamban (PLB) phosphorylation relieves cardiac sarcoplasmic reticulum (SR) Ca2+-pump ATPase, a critical regulator in intracellular Ca2+ cycling, from inhibition. To test the hypothesis that IHA hypoxia increases PLB phosphorylation and that such an effect plays a role in cardioprotection, we compared the time-dependent changes in the PLB phosphorylation at Ser16 (PKA site) and Thr17 (CaMKII site) in perfused normoxic rat hearts with those in IHA hypoxic rat hearts submitted to 30-min ischemia (I30) followed by 30-min reperfusion (R30). IHA hypoxia improved postischemic contractile recovery, reduced the maximum extent of ischemic contracture, and attenuated I/R-induced depression in Ca2+-pump ATPase activity. Although the PLB protein levels remained constant during I/R in both groups, Ser16 phosphorylation increased at I30 and 1 min of reperfusion (R1) but decreased at R30 in normoxic hearts. IHA hypoxia upregulated the increase further at I30 and R1. Thr17 phosphorylation decreased at I30, R1, and R30 in normoxic hearts, but IHA hypoxia attenuated the depression at R1 and R30. Moreover, PKA inhibitor H89 abolished IHA hypoxia-induced increase in Ser16 phosphorylation, Ca2+-pump ATPase activity, and the recovery of cardiac performance after ischemia. CaMKII inhibitor KN-93 also abolished the beneficial effects of IHA hypoxia on Thr17 phosphorylation, Ca2+-pump ATPase activity, and the postischemic contractile recovery. These findings indicate that IHA hypoxia mitigates I/R-induced depression in SR Ca2+-pump ATPase activity by upregulating dual-site PLB phosphorylation, which may consequently contribute to IHA hypoxia-induced cardioprotection against I/R injury.

scholarly journals Oxidation of ryanodine receptor after ischemia-reperfusion increases propensity of Ca2+ waves during β-adrenergic receptor stimulation

2018 ◽  
Vol 315 (4) ◽  
pp. H1032-H1040 ◽  
Author(s):  
Elisa Bovo ◽  
Stefan R. Mazurek ◽  
Aleksey V. Zima
Keyword(s):  
Oxidative Stress ◽  
Sarcoplasmic Reticulum ◽  
Ryanodine Receptor ◽  
Adrenergic Receptor ◽  
Positive Inotropic Effect ◽  
Ischemia Reperfusion ◽  
Critical Role ◽  
Inotropic Effect ◽  
Adrenergic Stimulation ◽  
Promising Strategy

β-Adrenergic receptor (β-AR) activation produces the main positive inotropic response of the heart. During ischemia-reperfusion (I/R), however, β-AR activation can trigger life-threatening arrhythmias. Because I/R is frequently associated with oxidative stress, we investigated whether ryanodine receptor (RyR) oxidation contributes to proarrythmogenic Ca2+ waves during β-AR activation. Measurements of contractile and electrical activity from Langendorff-perfused rabbit hearts revealed that I/R produces tachyarrhythmias. Ventricular myocytes isolated from I/R hearts had an increased level of oxidized glutathione (i.e., oxidative stress) and a decreased level of free thiols in RyRs (i.e., RyR oxidation). Furthermore, myocytes from I/R hearts were characterized by increased sarcoplasmic reticulum (SR) Ca2+ leak and enhanced fractional SR Ca2+ release. In myocytes from nonischemic hearts, β-AR activation with isoproterenol (10 nM) produced only a positive inotropic effect, whereas in myocytes from ischemic hearts, isoproterenol at the same concentration triggered spontaneous Ca2+ waves. β-AR activation produced a similar effect on RyR phosphorylation in control and I/R myocytes. Treatment of myocytes from I/R hearts with the reducing agent mercaptopropionylglycine (100 μM) attenuated RyR oxidization and decreased Ca2+ wave frequency during β-AR activation. On the other hand, treatment of myocytes from nonischemic hearts with H2O2 (50 μM) increased SR Ca2+ leak and triggered Ca2+ waves during β-AR activation. Collectively, these results suggest that RyR oxidation after I/R plays a critical role in the transition from positive inotropic to arrhythmogenic effects during β-AR stimulation. Prevention of RyR oxidation can be a promising strategy to inhibit arrhythmias and preserve positive inotropic effect of β-AR activation during myocardial infarction. NEW & NOTEWORTHY Oxidative stress induced by ischemia plays a critical role in triggering arrhythmias during adrenergic stimulation. The combined increase in sarcoplasmic reticulum Ca2+ leak (because of ryanodine receptor oxidation) and sarcoplasmic reticulum Ca2+ load (because of adrenergic stimulation) can trigger proarrythmogenic Ca2+ waves. Restoring normal ryanodine receptor redox status can be a promising strategy to prevent arrhythmias and preserve positive inotropic effect of adrenergic stimulation during myocardial infarction.

Calcium channels and excitation–contraction coupling in cardiac cells. II. A pharmacological study of the biphasic contraction in guinea-pig papillary muscle

1987 ◽  
Vol 65 (9) ◽  
pp. 1832-1839 ◽  
Author(s):  
E. Honoré ◽  
M. M. Adamantidis ◽  
B. A. Dupuis ◽  
C. E. Challice ◽  
P. Guilbault
Keyword(s):  
Guinea Pig ◽  
Papillary Muscle ◽  
Positive Inotropic Effect ◽  
Pharmacological Study ◽  
Negative Inotropic Effect ◽  
Cardiac Cells ◽  
Inotropic Effect ◽  
Free Solution ◽  
Contraction Coupling ◽  
Rich Solution

Biphasic contractions were obtained in guinea-pig papillary muscle by inducing partial depolarization in K+-rich solution (17 mM) in the presence of 0.3 μM isoproterenol. Mn2+ ions inhibited the two components of contraction in a similar way. Nifedipine and particularly Cd2+ ions specifically inhibited the second component of contraction. Isoproterenol and BAY K 8644 markedly increased the amplitude of the second component (P2) of contraction. Nevertheless, a moderate positive inotropic effect of isoproterenol was found on the first component (P1) of contraction when excitability was restored by 0.2 mM Ba instead of isoproterenol. Acetylcholine and hypoxia decreased the amplitude of the second component of contraction to a greater extent. In the presence of digoxin or Na+-free solution, P1was strongly increased. When sarcoplasmic reticular function was hindered by 1 mM caffeine or in the presence of Ca2+-free Sr2+ solution, digoxin always induced a negative inotropic effect on P2. Inversely in these conditions the transient positive inotropic effect of Na+-free solution was strongly reduced. These results are consistent with the hypothesis that the late component of contraction is triggered by the slow inward Ca2+ current and that the early component is due to Ca2+ release from the sarcoplasmic reticulum.

Positive inotropic effects of low concentrations of leukotrienes C4 and D4 in rat heart

1990 ◽  
Vol 259 (4) ◽  
pp. H1239-H1246 ◽  
Author(s):  
M. Karmazyn ◽  
M. P. Moffat
Keyword(s):  
Calcium Channel ◽  
Positive Inotropic Effect ◽  
Negative Inotropic Effect ◽  
Bay K 8644 ◽  
Inotropic Effect ◽  
Receptor Interaction ◽  
Inotropic Effects ◽  
Coronary Pressure ◽  
Low Concentrations ◽  
Rat Hearts

We examined the effects of leukotrienes (LT) B4, C4, D4, and E4 (0.010-2.5 ng/ml) on contractile and coronary function in isolated rat hearts. Concentration-dependent effects were examined either by the cumulative addition of LTs or by addition of specific concentrations to individual preparations. Neither LTB4 nor LTE4 produced myocardial or coronary effects at any concentration, irrespective of addition protocol. At 0.010 ng/ml, both LTC4 and LTD4 produced an increase in force that was associated with a 30% elevation in coronary pressure. Further cumulative addition of either leukotriene resulted in a negative inotropic effect and a further increase in coronary pressure. In contrast, following single additions of LTC4 or LTD4 (0.01-0.50 ng/ml) a positive inotropic effect and an increased coronary pressure were observed. LTC4 or LTD4 at 0.5 ng/ml produced a negative inotropic effect in hearts pretreated with 0.01 ng/ml of LTD4 or LTC4, respectively. Reversal of this addition protocol resulted in a negative inotropic effect of either 0.01 ng/ml LTD4 or LTC4. Verapamil and nifedipine significantly attenuated the positive inotropic and coronary constricting effect of 0.5 ng/ml LTC4 and LTD4. The addition of either LT following BAY K 8644 resulted in a negative inotropic effect, in contrast to the positive inotropic influence seen with leukotriene alone. Our results demonstrate a positive inotropic effect of low concentrations of LTC4 and LTD4 concomitant with coronary artery constriction, a phenomenon determined by leukotriene addition protocols and suggestive of LTC4/LTD4 receptor interaction. The effects of calcium channel antagonists and BAY K 8644 on the inotropic response suggest a leukotriene-mediated activation of the calcium channel resulting in increased intracellular calcium concentrations.

Some Effects of Caffeine and Quinidine on Sarcoplasmic Reticulum of Skeletal and Cardiac Muscle

1973 ◽  
Vol 51 (7) ◽  
pp. 499-503 ◽  
Author(s):  
William R. Thorpe
Keyword(s):  
Skeletal Muscle ◽  
Sarcoplasmic Reticulum ◽  
Cardiac Muscle ◽  
Myocardial Contractility ◽  
Gastrocnemius Muscle ◽  
Negative Inotropic Effect ◽  
Inotropic Effect ◽  
Experimental Conditions

Sarcoplasmic reticulum (SR) was prepared from the gastrocnemius muscle and the heart of freshly killed rabbits. It was found that the skeletal SR actively bound significantly more calcium than did the cardiac SR under the same experimental conditions. The effect of caffeine and quinidine on the release of calcium actively bound by both cardiac and skeletal SR was studied. Quinidine (10−3 M) released 4.1% of the calcium bound by skeletal SR and 27.7% of that bound by cardiac SR. Similarly, caffeine (20 mM) released 10.5% and 34.3% of the calcium bound by skeletal and cardiac SR, respectively. It is suggested that both caffeine and quinidine could produce contracture of skeletal muscle by acting on the SR and that caffeine could stimulate myocardial contractility through its action on the cardiac SR. However, it is unlikely that quinidine exerts its negative inotropic effect on the heart through its calcium releasing action on the cardiac SR.

Exercise prevents diabetes-induced impairment in superficial buffer barrier in porcine coronary smooth muscle

2004 ◽  
Vol 96 (3) ◽  
pp. 1069-1079 ◽  
Author(s):  
C. A. Witczak ◽  
M. Sturek
Keyword(s):  
Smooth Muscle ◽  
Sarcoplasmic Reticulum ◽  
Atpase Activity ◽  
Smooth Muscle Cells ◽  
Muscle Cells ◽  
Diabetic Dyslipidemia ◽  
Coronary Smooth Muscle ◽  
Treatment Groups ◽  
Analysis Techniques ◽  
Intracellular Ca

In healthy coronary smooth muscle cells, the superficial sarcoplasmic reticulum (SR) buffers rise in intracellular Ca2+ levels. In diabetic dyslipidemia, basal Ca2+ levels are increased, yet Ca2+ influx is decreased and SR Ca2+ uptake is increased. Exercise prevents diabetic dyslipidemia-induced increases in basal Ca2+ levels and decreases in Ca2+ influx. We tested the hypothesis that diabetic dyslipidemia impairs Ca2+ extrusion via a decrease in superficial SR and that exercise will prevent these losses. Male Yucatan swine were maintained in four treatment groups: control, hyperlipidemic, diabetic dyslipidemic, and diabetic dyslipidemic plus aerobically exercise trained. Intracellular Ca2+ levels were measured during depolarization-induced Ca2+ influx and caffeine-induced SR Ca2+ release. Na+/Ca2+ exchanger and plasmalemmal Ca2+-ATPase activity were assessed by inhibition with low extracellular Na+ and 5,6-carboxyeosin, respectively. Superficial SR was quantified using the internal membrane dye 3,3′-dihexyloxacarbocyanine iodide (DiOC6) and novel analysis techniques. We found that, in diabetic dyslipidemia, Ca2+ extrusion was impaired and superficial SR was decreased. Exercise prevented the diabetic dyslipidemia-induced decrease in superficial SR and restored plasmalemmal Ca2+ extrusion. On the basis of these results, we conclude exercise attenuates the diabetic dyslipidemia-induced impairment in intracellular Ca2+ regulation.

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