Paradoxical effects of cardiac arrest by multidose potassium cardioplegia on myocardial lysosome integrity and phospholipid content

Multidose potassium cardioplegia is known to result in greater preservation of myocardial ATP content and better recovery of function as compared to cardiac arrest induced by aortic clamping. The present study was undertaken to assess the effects of this procedure on biochemical markers of tissue damage. Rat hearts undergoing either multidose cardioplegia or ischemic cardiac arrest were maintained at 18 degrees C for 1 or 2 hr and processed without reperfusion. Control hearts were processed at time zero. The activity of two lysosomal enzymes (beta-glucuronidase and acid phosphatase), as well as membrane phospholipid content, was measured in cardiac homogenates. One hour of arrest by either technique did not induce significant changes in these parameters. Two hours of arrest affected lysosomal integrity, as indicated by release of lysosomal enzymes into the cytosol. Soluble acid phosphatase activity averaged 44.7 +/- 1.3 mU/mg of protein in the hearts processed after 2 hr of cardioplegic arrest, and was significantly higher than that of control hearts (12.3 +/- 3.8 mU/mg of protein; P less than 0.01) and that of hearts subjected to 2 hr of ischemic arrest (29.2 +/- 4.5 mU/mg of protein; P less than 0.01 vs cardioplegic arrest; P less than 0.01 vs controls). Phospholipid content in hearts subjected to 2 hr of cardioplegic arrest was lower than in controls (0.49 +/- 0.06 micrograms Pi/mg of protein vs 0.76 +/- 0.03 micrograms Pi/mg of protein; P less than 0.01). In conclusion, 2 hr of hypothermic cardiac arrest was associated with biochemical indices of tissue damage.(ABSTRACT TRUNCATED AT 250 WORDS)     

The significance of multidose cardioplegia and hypothermia in myocardial preservation during ischemic arrest

A standard experimental protocol was developed to explore the optimal technique for myocardial preservation during 120 minutes of ischemic arrest followed by 30 minutes of reperfusion. Eight different experimental groups were evaluated with the use of an in vivo pig heart preparation. The parameters measured included myocardial contractility and compliance, myocardial blood flow, and endocardial/epicardial blood flow ratio. Myocardial preservation was inadequate after hypothermic arrest alone, cardioplegic arrest alone (at normothermia), and single-dose cardioplegia plus hypothermia. Adequate myocardial preservation was found only after hypothermia and multidose cardioplegia with either potassium (35 mEq. per liter) or magnesium-procaine solutions. Continuous cardioplegia and hypothermia, while providing a moderate degree of myocardial preservation, was not as satisfactory as multidose cardioplegia and hypothermia. No difference in myocardial preservation was apparent when potassium-induced cardioplegia was compared with magnesium-procaine-induced cardioplegia.     

Amelioration of reperfusion injury following hypothermic, ischemic cardioplegia in isolated, infarcted rat hearts

The left coronary artery was ligated and myocardial infarction developed in 28 rats. Three weeks later, the hearts were excised and mounted in an apparatus for perfusion of non-working isolated hearts (Langendorff). Hypothermic (15 degrees C), ischemic cardioplegia was induced for either 2 or 3 1/2 h followed by reperfusion for 45 min. Half of the hearts were reperfused with an initially gradual rise in temperature and pressure of the perfusion fluid, whereas the other half was reperfused directly with the perfusate at 37 degrees C and 100 cm H2O pressure. The hearts were examined by transmission electron microscopy and randomized for stereological analysis based on point counting on electron micrographs. Cardioplegia of 2 h duration was tolerated better than cardioplegia for 3 1/2 h (interstitial edema; P = 0.03, fraction of altered mitochondria; P = 0.001). Particularly in the hearts undergoing the longest cardioplegia, myocardial injury was less severe following a gentle reperfusion as compared with those exposed to the clinically common abrupt technique (fraction of mitochondria in the myocyte; P = 0.03, fraction of altered mitochondria; P = 0.008). In the interstitium, the luminal area of capillaries was significantly increased and the endothelial swelling less pronounced in the groups undergoing the gentle reperfusion technique, (luminal/endothelial fraction; P = 0.01). The study shows that previously infarcted hearts are susceptible to ischemic damage even after 2 h of regular hypothermic, ischemic cardioplegia and that a gentle reperfusion technique significantly ameliorates reperfusion injury.     

Improved energy preservation following gentle reperfusion after hypothermic, ischemic cardioplegia in infarcted rat hearts

The influence of temperature and pressure during early reperfusion after 2 h of hypothermic, cardioplegic ischemia was investigated. Adenosine triphosphate (ATP) and creatinephosphate (CP) were measured after 45-min reperfusion. The experiments were carried out in normal and previously infarcted rat hearts (the left coronary artery having been ligated 3 weeks carlier). Four groups, each containing six hearts, were studied. Group 1 consisted of normal hearts reperfused with an abrupt rise in temperature and pressure, group 2 of normal hearts exposed to slowly rising temperature and pressure, and group 3 and 4 of previously infarcted hearts. Reperfusion procedures in groups 3 and 4 were the same as in group 1 and 2, respectively. The study showed that previously infarcted hearts have a lowered tolerance to ischemia and that the reperfusion technique may influence the preservation of myocardial energetics, although this influence was not statistically significant in normal hearts following only 2 h of ischemia. The gently reperfused infarcted hearts had energy stores equal to the normal hearts after 2 h of ischemia and 45 min of reperfusion, whereas the infarcted hearts reperfused in a rougher mode had significantly lowered values (P<0.05 for ATP and P<0.01 for CP).     

Glucose metabolism,energetics, and function of rat hearts exposed to ischemic preconditioning and oxygenated cardioplegia

We examined changes induced during ischemia-reperfusion on myocardial metabolism and function by oxygenated warm cardioplegia (CP) and ischemic preconditioning (IP). The postischemic hemodynamic recovery was comparable and significantly better in IP and CP groups, than in untreated hearts (e.g., LVDP recovery was threefold that of the control). The IP hearts reached a pH plateau earlier during ischemia and at considerably higher pH value (pH approximately 6) compared to the other groups (pH approximately 5.5). Postischemic phosphocreatine (PCr) and ATP recoveries were comparable and better in protected groups (approximately 72% and approximately 30% vs approximately 25% and approximately 10% in control, p < 0.0001). Preischemic glycogen was significantly reduced in IP to 49% and increased in CP hearts to 127%. However, the lactate levels at the end of ischemia were similar in all the groups, indicating glucose utilization from extracellular space during ischemia in IP hearts. Thus, similar hemodynamic protection by CP and IP is observed despite increased energy depletion during ischemia in IP. IP and CP protection is expressed through better energetic status and by higher recovery of the TCA cycle activity or enhanced mitochondria-cytosol transport of alpha-ketoglutarate on reperfusion in addition to metabolic changes during ischemia. Glycogen store recovered significantly better in IP than in CP and Control. These results exhibit similar and improved postischemic hemodynamic protection by CP and IP. Increased recovery of postischemic glycogen pool is a protective feature of IP, whereas slightly higher lactate metabolism during reperfusion is a protection component of CP.     

Effect of experimental cardioplegia methods on normal and hypertrophied rat hearts

The purpose of this study was to evaluate whether the addition of verapamil hydrochloride to oxygenated glucose-rich cardioplegic solution would improve myocardial preservation. The Langendorff preparation of the isolated rat heart was used. Groups of normal (WKY) and hypertrophied (SHR) hearts were treated by five different cardioplegic methods and subjected to 90 or 30 minutes of ischemia at 28 degrees to 29 degrees C and reperfusion at 37 degrees C. The following cardioplegic solutions were used: Group A, cold (16 degrees C) Krebs-Henseleit (KH) glucose free only; Group B, KH with KCL (30 mEq/L) (16 degrees C); Group C, same as B with verapamil (10 microM); Group D, perfusion with oxygenated KH solution containing KCL (30 mEq/L) for 15 minutes prior to ischemia; and Group E, same as D with verapamil (10 microM). Recovery of contraction amplitude, ischemic contracture, coronary perfusate volume, the amount of creatine kinase in the coronary perfusate, heart rate, time of revival, O2 consumption, and ischemic contracture were measured. After 30 minutes of ischemia, we did not find any significant difference among the combinations tested with respect to contraction amplitude recovery. The hearts recovered fully. After 90 minutes of ischemia, we found that the best-protected groups in the normal hearts were Groups D and E. In the hypertrophied hearts, the addition of verapamil to the enhancement solution was harmful. The use of enhancement solution without verapamil prior to ischemia provided the best myocardial protection in the hypertrophied hearts.     

Protective effects of halothane on ischemic reperfusion injury on rat perfused hearts

We evaluated the possible cardioprotective effects of halothane in isolated rat hearts. Langendorff perfusion was initiated by using Krebs-Henseleit Buffer (KHB) heated at 37°C. Control group: After 15 mins Langendorff perfusion, global ischemia was induced for 40 mins at 37°C by clamping aorta, followed by 60 mins of reperfusion. Experimental group: Global ischemia was induced at the same time course as the control group and during reperfusion, halothane administered at the concentration of 1%, 2%, 3%. Cardiac function (heart rate, coronary flow, Vmax of the left ventricule) and intracelluar calcium level was measured during pre-ischemia, ischemia and reperfusion period. Recovery of cardiac function after ischemia was better in the 1% halothane group than in the control group but suppression on cardiac function inclined to increase concentration dependently. Compared to the control group, increase of intracellular calcium level after ischemia was suppressed in the halothane administered group at all concentration level. These data suggests that a low dose halothane administration shows a cardio-protective effects during reperfusion.     

Intramyocardial electrical and metabolic activity during hypothermia and potassium cardioplegia

Hypothermic potassium cardioplegia is widely used to reduce myocardial metabolism as a means of myocardial protection. To investigate the efficacy of intramyocardial electrical activity as an indicator of myocardial metabolism, 12 dogs were placed on cardiopulmonary bypass and myocardial oxygen consumption, partial pressure of carbon dioxide (PCO2) in the coronary sinus, myocardial temperature, and intramyocardial and surface electrocardiograms were measured. The hearts were fibrillated and cooled to 15 degrees C. In Group 1 (6 dogs), potassium cardioplegia was given at 15 degrees C. In Group 2 (6 dogs), it was given at 25 degrees C. Maximum coronary sinus PCO2 and oxygen consumption occurred at 36 degrees C and gradually decreased, but there was still evidence of metabolic activity and intramyocardial electrical activity at 15 degrees C. When cardioplegia was given at 15 degrees C, all electrical activity ceased and there was a further significant reduction in metabolic activity (coronary sinus PCO2 and oxygen consumption). In Group 2 similar findings were found at 25 degrees C, and there was no further reduction in metabolic activity at 15 degrees C. These data indicate that: (1) myocardial metabolic activity is lowest when there is electrical quiescence as measured with an intramyocardial electrode; (2) potassium arrest and hypothermia are both necessary to achieve electrical quiescence; and (3) in the potassium-arrested heart, lowering temperature from 25 degrees to 15 degrees C does not result in a further reduction of metabolic activity.     

Adenosine cardioplegia. Adenosine versus potassium cardioplegia: effects on cardiac arrest and postischemic recovery in the isolated rat heart

Adenosine is a potential cardioplegic agent by virtue of its specific inhibitory properties on nodal tissue. We tested the hypothesis that adenosine could be more effective than potassium in inducing rapid cardiac arrest and enhancing postischemic hemodynamic recovery. Isolated rat hearts were perfused with Krebs-Henseleit buffer or cardioplegic solutions to determine the time to cardiac arrest and the high-energy phosphate levels at the end of cardioplegia. Cardioplegic solutions contained adenosine 10 mmol/L, potassium 20 mmol/L, or adenosine 10 mmol/L + potassium 20 mmol/L and were infused at a rate of 2 ml/min for 3 minutes at 10 degrees C. Both time taken and total number of beats to cardiac arrest during 3 minutes of cardioplegia were reduced by adenosine 10 mmol/L and adenosine 10 mmol/L + potassium 20 mmol/L when compared with potassium 20 mmol/L alone (p less than 0.001). Tissue phosphocreatine was conserved by adenosine 10 mmol/L when compared with potassium 20 mmol/L, being 7.1 +/- 0.2 (mumol/gm wet weight (n = 7) and 6.0 +/- 0.3 mumol/gm wet weight (n = 5), respectively (p less than 0.05). Postischemic hemodynamic recovery was tested in isolated working rat hearts. After initial cardiac arrest, the cardioplegic solution was removed with Krebs-Henseleit buffer at a rate of 2 ml/min for 3 minutes at 10 degrees C, and thereafter total ischemia was maintained for 30 or 90 minutes at 10 degrees C before reperfusion. Adenosine 10 mmol/L enhanced recovery of aortic output when compared with potassium 20 mmol/L or adenosine 10 mmol/L + potassium 20 mmol/L, the percentage recovery after 30 minutes of ischemia being 103.0% +/- 4.4% (n = 6), 89.0% +/- 5.8% (n = 6), and 86.6% +/- 4.3% (n = 6), respectively (p less than 0.05 for comparison between adenosine 10 mmol/L and potassium 20 mmol/L). Thus adenosine cardioplegia caused rapid cardiac arrest and improved postischemic recovery when compared with potassium cardioplegia and with a combination of these two agents.     

缺血预处理对大鼠离体心脏心肌线粒体功能的影响

目的研究缺血预处理（IPC）对大鼠离体心脏心肌线粒体功能的影响。方法SD大鼠72只，随机分为4组（n=18）：对照组（CON组）、缺血再灌注组（IR组）、缺血预处理组（IPC组）和5-羟葵酸（5-HD）拮抗IPC组（5-HD＋IPC组）。采用Langendorff装置建立大鼠离体心脏缺血再灌注模型，IPC组在全心停灌前，给予2次缺血预处理，每次缺血5min，间隔5min；5-HD＋IPC组预处理前灌注5-HD 10min。各组于平衡末、缺血前、再灌注30min各取6个心脏，分离心肌线粒体并测定线粒体呼吸控制率（RCR）、磷氧比（ADP／O2）、NADH氧化酶（NADH-OX）、琥珀酸氧化酶（SUC-OX）、细胞色素C氧化酶（CYTC-OX）的活性。结果与CON组比较，IR组、IPC组和5-HD＋IPC组再灌注30min RCR、ADP／O2、NADH-OX、SUC-OX和CYTC＋OX的活性降低（P〈0．05）；与IR组比较，IPC组和5-HD＋IPC组再灌注30min上述各指标升高（P〈0．05）；与IPC组比较，5-HD＋IPC组再灌注30min上述各指标降低（P〈0．05）。结论缺血预处理可改善大鼠离体心脏缺血再灌注时心肌线粒体的功能，其机制与mitoKATP的激活有关。     

Functional effects of phosphoenolpyruvate and ATP on pig hearts in cardioplegia and during reperfusion. An in vivo study with cardiopulmonary bypass

The effects of phosphoenolpyruvate (PEP) and ATP in cardioplegia and during early reperfusion were studied in pigs. Twenty pigs divided into three groups were placed on cardiopulmonary bypass and subjected to 2 h of hypothermic cardioplegic arrest. Group I (n = 7) served as a control. In group II (n = 7) PEP (14.4 mM) and ATP (0.067 mM) were added to the cardioplegic solution. Group III (n = 6) was given PEP (28.8 mM) and ATP (0.134 mM) with 500 ml of isotonic NaCl in the aortic root during early reperfusion. All animals in group III were weaned from bypass compared with 6 of 7 in group I and 5 of 7 in group II. Forty minutes after ischemia group III was assessed to be the only group with an unchanged aortic flow and stroke volume. The total peripheral resistance and arterial pressure were reduced in this group. The results demonstrate that PEP and ATP administered during reperfusion have a beneficial effect and that this may be exerted both on the myocardium and on the peripheral vessels.     

Protective effects of halothane on ischemic reperfusion injury on rat perfused hearts]

We evaluated the possible cardioprotective effects of halothane in isolated rat hearts. Langendorff perfusion was initiated by using Krebs-Henseleit Buffer (KHB) heated at 37 degrees C. Control group: After 15 mins Langendorff perfusion, global ischemia was induced for 40 mins at 37 degrees C by clamping aorta, followed by 60 mins of reperfusion. Experimental group: Global ischemia was induced at the same time course as the control group and during reperfusion, halothane administered at the concentration of 1%, 2%, 3%. Cardiac function (heart rate, coronary flow, Vmax of the left ventricule) and intracelluar calcium level was measured during pre-ischemia, ischemia and reperfusion period. Recovery of cardiac function after ischemia was better in the 1% halothane group than in the control group but suppression on cardiac function inclined to increase concentration dependently. Compared to the control group, increase of intracellular calcium level after ischemia was suppressed in the halothane administered group at all concentration level. These data suggests that a low dose halothane administration shows a cardioprotective effects during reperfusion.     

The role of Na/H exchange in the efficacy of multidose hypothermic cardioplegia in immature rabbit hearts

Objectives: Recent studies have demonstrated that the use of a Na⁺/H⁺ exchange inhibitor as an additive can enhance the cardioprotective efficacy of cardioplegia in the adult heart under both normothermic and hypothermic conditions. However, few references are available as to the cardioprotective effect of acidic cardioplegia or Na⁺/H⁺ exchange inhibitors in the neonatal heart, particularly under hypothermic conditions. Methods and results: In isolated working hearts from rabbits aged 7–10 days, function was assessed prior to 10 h of ischemia (20 °C) and again after 35 min of reperfusion. All hearts received a pre-ischemic infusion (10 ml) of cardioplegic solution (20 °C) at pH 7.8, followed by nine subsequent infusions (5 ml every 1 h) of cardioplegic solution (20 °C) at pH 6.6, 7.0, 7.4, 7.8 (control) or 8.2 (n=8/group). When the pH was increased to 8.2, post-ischemic recovery of cardiac output was reduced and cumulative creatine kinase (CK) leakage during cardioplegic infusions was increased. In contrast, when the pH of the cardioplegic solution was lowered to 6.6, the post-ischemic recovery of cardiac output was maintained and CK leakage was reduced. Next, the effects of 5-(N,N-dimethyl)amiloride (DMA), an inhibitor of Na⁺/H⁺ exchange, were investigated. The inclusion of DMA in the pH 8.2 solution improved the post-ischemic recovery of cardiac output from 12.6±4.1% to 52.0±3.0% (P<0.0001) and reduced cumulative CK leakage during cardioplegic infusions from 38.0±4.0 to 26.1±3.7 IU/45 ml/g dry weight (P=0.044). In contrast, the inclusion of DMA in the pH 6.6 solution provided no added benefit. (Data are expressed as the mean±SEM.) Conclusions: These results suggest that the lesser efficacy of multidose hypothermic cardioplegia in the neonatal rabbit heart may depend on the pH of the cardioplegic solution and is likely to arise, at least in part, from activation of the Na⁺/H⁺ exchanger.     

Benefits of glucose and oxygen in multidose cold cardioplegia.

We tested the effects of glucose and oxygen in cardioplegic solutions on myocardial protection in the isolated perfused working rat heart. Recovery from 2 hours' hypothermic (8 degrees C) cardioplegic arrest was examined in 93 hearts. Cardioplegic solution, which was delivered every 15 minutes, was supplemented with glucose 28 mmol/L as a substrate or sucrose 28 mmol/L as a nonmetabolizable osmotic control; it was equilibrated with either 98% oxygen or 98% nitrogen, both with 2% carbon dioxide. Four combinations of hyperkalemic cardioplegic solution were studied: nitrogen-sucrose, nitrogen-glucose, oxygen-sucrose, and oxygen-glucose. During hypothermic arrest, oxygenation of cardioplegic solution greatly reduced myocardial lactate production and prevented ischemic contracture as indicated by coronary vascular resistance. Glucose increased lactate production modestly but significantly only when the cardioplegic solution was nitrogenated. Although end-arrest myocardial adenosine triphosphate and creatine phosphate were greatly increased by oxygenation of cardioplegic solution (p less than 0.005), we could not detect improved preservation of these high-energy phosphates by glucose. Averaged over reperfusion, percent recovery of cardiac output for the nitrogen-sucrose, nitrogen-glucose, oxygen-sucrose, and oxygen-glucose solutions was 32.3% +/- 6.1%, 45.9% +/- 4.6%, 44.5% +/- 4.6%, and 62.2% +/- 4.5%, respectively. Oxygenation of the glucose solution or addition of glucose to the oxygenated solution significantly improved recovery of cardiac output. The benefits of glucose and oxygen were additive, so that the oxygen-glucose cardioplegic solution provided the best functional recovery. We conclude that the addition of glucose to the fully oxygenated multidose cold cardioplegic solution improves functional recovery without increasing lactate production during arrest.     

Effect of multidose cardioplegia and cardioplegic solution buffering on myocardial tissue acidosis

Multidose administration of cardioplegic solution during cardiac operation is intended to maintain both electromechanical arrest of the heart and myocardial hypothermia as well as to remove accumulated metabolites of anaerobic glycolysis. This study was conducted to assess the effect of multidose infusion of three different types of cardioplegic solution on tissue acidosis during global myocardial ischemia. Three groups of five dogs each were placed on cardiopulmonary bypass and the aorta was cross-clamped for 3 hours. The hearts were maintained at a constant temperature (20 degrees C) and cardioplegic solution was infused at an initial dose of 500 ml and five supplementary doses of 250 ml administered every 30 minutes. Group 1 received a crystalloid solution weakly buffered with sodium bicarbonate, Group 2 received a blood-based solution, and Group 3 received a crystalloid solution strongly buffered with histidine (Bretschneider's solution). The buffering capacities of the solutions used in Groups 2 and 3 were 40 and 60 times, respectively, that of the solution used in Group 1. The average myocardial tissue pH at the end of 3 hours of ischemia was 6.54 +/- 0.07 in Group 1, 7.23 +/- 0.05 in Group 2, and 7.19 +/- 0.06 in Group 3 (Group 1 significantly lower than Groups 2 and 3). Multidose infusion of a cardioplegic solution with low buffering capacity was unable to prevent the progressive development of tissue acidosis during 3 hours of ischemia. However, the multidose infusion of either blood-based or crystalloid solutions with high buffering capacity completely prevented any further reduction of tissue pH after the first 30 minutes of ischemia.     

A clinical comparison of potassium and magnesium-potassium crystalloid cardioplegia: metabolic considerations

Controlled metabolic studies were used to gauge the relative efficacy of two cardioplegic solutions in 28 patients (14 in each group) undergoing multiple coronary artery bypass grafts. A solution containing magnesium-potassium (Plegisol) was compared to a standard potassium crystalloid cardioplegic solution. Measurements of coronary blood flow, coronary vascular resistance, coronary arteriovenous oxygen difference, myocardial oxygen consumption and extraction, and myocardial lactate and potassium extraction and release were all measured in the isolated, vented, paced, beating heart, before and for 15 minutes after a one hour arrest interval during which time revascularization was completed. During cardioplegic administration, the infusion flow rate, myocardial oxygen consumption and extraction, and lactate and potassium release and uptake were noted. The results indicate that during cardioplegic administration, the total oxygen consumed for both potassium and magnesium-potassium solutions did not significantly differ. The flow rate of the Mg-K solution was significantly higher than that of the potassium solution alone (510 vs. 398 ml/min). There was no lactate production during Mg-K administration, but 0.13 mEq/min of lactate was produced while potassium crystalloid cardioplegia was given. During myocardial reperfusion, oxygen extraction was maintained near prearrest levels in both groups. The only significant difference noted between the potassium and magnesium-potassium solutions were the higher coronary blood flow and oxygen consumption immediately upon reperfusion in the Mg-K group.(ABSTRACT TRUNCATED AT 250 WORDS)     

Protein kinase C isoform-dependent myocardial protection by ischemic preconditioning and potassium cardioplegia

OBJECTIVE: Ischemic preconditioning combined with potassium cardioplegia does not always confer additive myocardial protection. This study tested the hypothesis that the efficacy of ischemic preconditioning under potassium cardioplegia is dependent on protein kinase C isoform. METHODS: Isolated and crystalloid-perfused rat hearts underwent 5 cycles of 1 minute of ischemia and 5 minutes of reperfusion (low-grade ischemic preconditioning) or 3 cycles of 5 minutes of ischemia and 5 minutes of reperfusion (high-grade ischemic preconditioning) or time-matched continuous perfusion. These hearts received a further 5 minutes of infusion of normal buffer or oxygenated potassium cardioplegic solution. The isoform nonselective protein kinase C inhibitor chelerythrine (5 micromol/L) was administered throughout the preischemic period. All hearts underwent 35 minutes of normothermic global ischemia followed by 30 minutes of reperfusion. Isovolumic left ventricular function and creatine kinase release were measured as the end points of myocardial protection. Distribution of protein kinase C alpha, delta, and epsilon in the cytosol and the membrane fractions were analyzed by Western blotting and quantified by a densitometric assay. RESULTS: Low-grade ischemic preconditioning was almost as beneficial as potassium cardioplegia in improving functional recovery; left ventricular developed pressure 30 minutes after reperfusion was 70 +/- 15 mm Hg (P <.01) in low-grade ischemic preconditioning and 77 +/- 14 mm Hg (P <.001) in potassium cardioplegia compared with values found in unprotected control hearts (39 +/- 12 mm Hg). Creatine kinase release during reperfusion was also equally inhibited by low-grade ischemic preconditioning (18.2 +/- 10.6 IU/g dry weight, P <.05) and potassium cardioplegia (17.6 +/- 6.7 IU/g, P <.01) compared with control values. However, low-grade ischemic preconditioning in combination with potassium cardioplegia conferred no significant additional myocardial protection; left ventricular developed pressure was 80 +/- 17 mm Hg, and creatine kinase release was 14.8 +/- 11.0 IU/g. In contrast, high-grade ischemic preconditioning with potassium cardioplegia conferred better myocardial protection than potassium cardioplegia alone; left ventricular developed pressure was 121 +/- 16 mm Hg (P <.001), and creatine kinase release was 8.3 +/- 5.8 IU/g (P <.05). Chelerythrine itself had no significant effect on functional recovery and creatine kinase release in the control hearts, but it did inhibit the salutary effects not only of low-grade and high-grade ischemic preconditioning but also those of potassium cardioplegia. Low-grade ischemic preconditioning and potassium cardioplegia enhanced translocation of protein kinase C alpha to the membrane, whereas high-grade ischemic preconditioning also enhanced translocation of protein kinase C delta and epsilon. Chelerythrine inhibited translocation of all 3 protein kinase C isoforms. CONCLUSIONS: These results suggest that myocardial protection by low-grade ischemic preconditioning and potassium cardioplegia are mediated through enhanced translocation of protein kinase C alpha to the membrane. It is therefore suggested that activation of the novel protein kinase C isoforms is necessary to potentiate myocardial protection under potassium cardioplegia.