Acetaminophen in the hypoxic and reoxygenated guinea pig myocardium

We investigated the effects of 0.35-mM acetaminophen and its vehicle on isolated, perfused guinea pig hearts made hypoxic and subsequently reoxygenated. Hearts were allowed 30 min postinstrumentation to reach baseline, steady-state values, and then were exposed to 6 min of hypoxia (5% O(2), 5% CO(2), balance N(2)) followed by 36 min of reoxygenation (95% O(2), 5% CO(2)). We recorded hemodynamic, metabolic, and mechanical data in addition to assessing ultrastructure and the capacity of coronary venous effluent to reduce reactive oxygen species. We found that acetaminophen-treated hearts retained a greater fraction of mechanical function during hypoxia and reoxygenation. For example, the average percentage change from baseline of left ventricular developed pressure in acetaminophen- and vehicle-treated hearts at 6 min reoxygenation was 9 +/- 2% and -8 +/- 5% (P < 0.05), respectively. In addition, electron micrographs revealed greater preservation of myofibrillar ultrastructure in acetaminophen-treated hearts. Biochemical analyses revealed the potential of coronary effluent from acetaminophen-treated hearts to significantly neutralize peroxynitrite-dependent chemiluminescence in all recorded time periods. During early reoxygenation, the percentage inhibition of peroxynitrite-mediated chemiluminescence was 56 +/- 10% in vehicle-treated hearts and 99 +/- 1% in acetaminophen-treated hearts (P < 0.05). We conclude that acetaminophen has previously unreported cardioprotective properties in the nonischemic, hypoxic, and reoxygenated myocardium mediated through the reduction of reactive oxygen species.     

Energy dependence of enzyme release from hypoxic isolated perfused rat heart tissue

There is a sudden release of intracellular constituents upon reoxygenation of isolated perfused hypoxic heart tissue (O2 paradox) or on perfusion with calcium-free medium after a period of hypoxia. Rat hearts were perfused by the method of Langendorff (Pfluegers Arch. 61: 291-332, 1895) with Krebs-Henseleit medium containing 10 mM glucose. Hearts were equilibrated for 30 min, followed by 90 min of hypoxia or 60 min of hypoxia and 30 min of reoxygenation. The massive enzyme release observed upon reoxygenation after 60 min of hypoxia was prevented by infusing 0.5 or 5 mM cyanide 5 min before reoxygenation. Lactate dehydrogenase (LDH) release commenced immediately upon withdrawal of cyanide. Hearts perfused with calcium-free medium throughout hypoxia did not release increased amounts of LDH at reoxygenation. Perfusing heart tissue with medium containing 0 or 25 microM calcium, but not 0.25 or 2.5 mM, after 50 min of hypoxia initiated a release of cardiac LDH, which was not further enhanced by reoxygenation. Enzyme release was significantly inhibited when the calcium-free perfusion medium included 10 mM 2-deoxyglucose (replacing glucose), 0.5 mM dinitrophenol, or 2.5 mM cyanide. Histologically, hearts perfused with calcium-free medium after 50 min of hypoxia showed areas of severe necrosis and contracture without any evidence of the contraction bands that were seen in hearts reoxygenated in the presence of calcium. Cardiac ATP and creatine phosphate (PCr) levels were significantly decreased after 50-60 min of hypoxia.(ABSTRACT TRUNCATED AT 250 WORDS)     

The Glutathione Status of Perfused Rat Hearts Subjected to Hypoxia and Reoxygenation: The Oxygen Paradox

Langendorff perfused rat hearts subjected to 30min hypoxia followed by 20min reoxygenation and the levels of the oxidised and reduced forms of glutathione measured. No change in the concentration of oxidised glutathione was detected in reoxygenated hearts when compared to normoxic controls. In contrast hearts exposed to oxidative stress in the form of H₂O₂ showed elevated levels of both oxidised glutathione (GSSG) and the glutathione-protein mixed disulphide. These results suggest that if oxidants do contribute to cell damage on reoxygenation of the hypoxic myocardium then their action is local and not through overwhelming of the cells antioxidant defences.     

Electrophysiological effects of ethmozine in perfused rabbit hearts

His-bundle electrocardiography was used to evaluate the effects of ethmozine on cardiac conduction in isolated perfused rabbit hearts electrically driven at cycle lengths of 320 and 250 ms. There was no significant change in conduction until high concentrations of ethmozine were reached. His-Purkinje and atrioventricular (AV) nodal conduction were slowed significantly at 0.1 microgram/mL and atrial conduction at 1.0 microgram/mL. Conduction block occurred at 10.0 micrograms/mL in all the hearts treated. Effects of the drug (0.1 and 0.01 microgram/mL) on conduction of extrasystoles were also studied in hearts driven at a basic cycle length of 270 ms. No significant change was observed in atrial conduction of extrasystoles throughout the coupling intervals tested at both concentrations. Ethmozine (0.01 and 0.1 microgram/mL) caused slowing of His-Purkinje conduction of extrasystoles but the effect of the drug did not change as a function of the coupling interval. An interval-dependent increase in AV-nodal conduction time was observed, with the maximum slowing of conduction occurring at coupling intervals close to the effective refractory period of the AV node. AV-nodal functional refractory period was increased significantly by ethmozine (0.01 and 0.1 microgram/mL). The effective refractory period was significantly increased only at the higher concentration.     

Importance of fatty acid oxidation in the neonatal pig heart with hypoxia and reoxygenation

We investigated mechanical and metabolic responses in isolated, isovolumically-beating, pig hearts (n = 7), 12 h to 2 days of age; subjected to hypoxia followed by reoxygenation. Hearts were perfused with an erythrocyte-enriched (hematocrit approximately 15%) solution during 3 consecutive 30-min periods: pre-hypoxia, arterial perfusate [O2] = 7.6 +/- 0.2 vol% (PO2 approximately 270 torr); hypoxia, [O2] = 0.6 +/- 0.1 vol% (approximately 10% hemoglobin saturation) and reoxygenation. Prehypoxia parameters averaged: left ventricular peak systolic pressure, 107.1 +/- 2.9 mmHg and end-diastolic pressure, 0.9 +/- 0.3 mmHg; coronary flow, 2.8 +/- 0.2 ml/min per g; myocardial O2 consumption, 59.4 +/- 1.6 microliters/min per g and fatty acid oxidation, 37.1 +/ 1.1 nmol/min per g. Fatty acid oxidation was determined using [14C]palmitate. Early in hypoxia, coronary flow increased 3-4 fold but then decreased. Throughout hypoxia, hearts released lactate yet continued to oxidize fatty acids (45-50% of myocardial O2 consumption). By the end of the hypoxia period, hearts exhibited mechanical failure (peak systolic pressure approximately 55 mmHg and end-diastolic pressure approximately 19 mmHg). After 30 min of reoxygenation, peak systolic pressure recovered to 80.6 +/- 2.6 mmHg and end-diastolic pressure remained elevated at 6.1 +/- 1.9 mmHg. However, fatty acid oxidation rates were 90-95% above pre-hypoxia values. Thus, during 30 min of severe hypoxia neonatal pig hearts exhibited mechanical dysfunction, yet continued to oxidize exogenously supplied fatty acids. Moreover, fatty acid oxidation was enhanced during reoxygenation.     

The Glutathione Status of Perfused Rat Hearts Subjected to Hypoxia and Reoxygenation: The Oxygen Paradox

Langendorff perfused rat hearts subjected to 30min hypoxia followed by 20min reoxygenation and the levels of the oxidised and reduced forms of glutathione measured. No change in the concentration of oxidised glutathione was detected in reoxygenated hearts when compared to normoxic controls. In contrast hearts exposed to oxidative stress in the form of H₂O₂ showed elevated levels of both oxidised glutathione (GSSG) and the glutathione-protein mixed disulphide. These results suggest that if oxidants do contribute to cell damage on reoxygenation of the hypoxic myocardium then their action is local and not through overwhelming of the cells antioxidant defences.     

ROS are required for rapid reactivation of Na+/Ca2+ exchanger in hypoxic reoxygenated guinea pig ventricular myocytes

The cardiac Na(+)/Ca(2+) exchanger (NCX) contributes to cellular injury during hypoxia, as its altered function is largely responsible for a rise in cytosolic Ca(2+) concentration ([Ca(2+)](i)). In addition, the NCX in guinea pig ventricular myocytes undergoes profound inhibition during hypoxia and rapid reactivation during reoxygenation. The mechanisms underlying these changes in NCX activity are likely complex due to the participation of multiple inhibitory factors including altered cytosolic Na(+) concentration, pH, and ATP. Our main hypothesis is that oxidative stress is an essential trigger for rapid NCX reactivation in guinea pig ventricular myocytes and is thus a critical factor in determining the timing and magnitude of Ca(2+) overload. This hypothesis was evaluated in cardiac myocytes using fluorescent indicators to measure [Ca(2+)](i) and oxidative stress. An NCX antisense oligonucleotide was used to decrease NCX protein expression in some experiments. Our results indicate that NCX activity is profoundly inhibited in hypoxic guinea pig ventricular myocytes but is reactivated within 1-2 min of reoxygenation at a time of rising oxidative stress. We also found that several interventions to decrease oxidative stress including antioxidants and diazoxide prevented NCX reactivation and Ca(2+) overload during reoxygenation. Furthermore, application of exogenous H(2)O(2) was sufficient by itself to reactivate the NCX during sustained hypoxia and could reverse the suppression of reoxygenation-mediated NCX reactivation by diazoxide. These data suggest that elevated oxidative stress in reoxygenated guinea pig ventricular myocytes is required for rapid NCX reactivation, and thus reactivation should be viewed as an active process rather than being due to the simple decline of NCX inhibition.     

Mechanism of hypoxic preconditionin in guinea pig papillary muscles

Brief ischemia or hypoxia has been found to protect the heart against susbsequent long-lasting ischemia and to improve contractile dysfunction as well to reduce cell necrosis and the incidence of lethal arrhythmias. This phenomenon, termed preconditioning (PC) has been demonstrated in different species. However, little is known about PC in guinea pigs. Moreover, electrophysiological changes underlying protection have not been studied so far in conjuntion with force recovery in a setting of PC. The aim of the study was to study PC in a guinea pig papillary muscle, using recovery of contractility after long hypoxic challenge as the main end-point of protection, and to investigate concominant electrophysiological alterations. In guinea pig papillary muscle preparations contracting isometrically (paced at 2 Hz), transmembrane action potentials (AP) and developed force (DF) were recorded by conventional microelectrode technique and a force tranducer. In addition, effective refractory periods (ERP) were determined. Hypoxia was induced by superfusion with 100% N₂ (pO₂ < 5 kPa) and pacing at 3,3 Hz. In the control group, long hypoxia lasted for 45 min and was followed by 30 min reoxygenation. In the PC group, muscles were subjected to 5 min hypoxia followed by 10 min recovery prior to sustained hypoxia/reoxygenation. Results: Long hypoxia induced a similar depression of DF in both, PC and control groups. However, a loss of contractile activity occured earlier in the PC group. AP duration and ERP decreased faster and were significantly shorter after PC. Upon reoxygenation, preconditioned muscles showed significantly better recovery of function (DF 86% of prehypoxic value vs. 36% in controls; p < 0,05). AP and ERP were completely restored in both, PC and control groups. Guinea pig papillary muscle can be preconditioned with a brief hypoxic challenge against contractile dysfunction upon long-lasting hypoxia/reoxygenation. Shortening of AP and loss of contractility occured more quickly during hypoxia and may participate in the protective effect of preconditioning. Possible mechanisms might involve facilitated opening of K_ATP-dependent channels.     

Acetaminophen-mediated cardioprotection via inhibition of the mitochondrial permeability transition pore-induced apoptotic pathway

Our laboratory has previously reported that acetaminophen confers functional cardioprotection following cardiac insult, including ischemia/reperfusion, hypoxia/reoxygenation, and exogenous peroxynitrite administration. In the present study, we further examined the mechanism of acetaminophen-mediated cardioprotection following ischemia/reperfusion injury. Langendorff-perfused guinea pig hearts were exposed to acute treatment with acetaminophen (0.35 mM) or vehicle beginning at 15 min of a 30-min baseline stabilization period. Low-flow global myocardial ischemia was subsequently induced for 30 min followed by 60 min of reperfusion. At the completion of reperfusion, hearts were homogenized and separated into cytosolic and mitochondrial fractions. Mitochondrial swelling and mitochondrial cytochromec release were assessed and found to be significantly and completely reduced in acetaminophen- vs. vehicle-treated hearts following reperfusion. In a separate group of hearts, ventricular myocytes were isolated and subjected to fluorescence-activated cell sorting. Acetaminophen-treated hearts showed a significant decrease in late stage apoptotic myocytes compared with vehicle-treated hearts following injury (58 +/- 1 vs. 81 +/- 5%, respectively). These data, together with electron micrograph analysis, suggest that acetaminophen mediates cardioprotection, in part, via inhibition of the mitochondrial permeability transition pore and subsequent apoptotic pathway.     

Antioxidant changes in heart hypertrophy: significance during hypoxia-reoxygenation injury.

Because hypertrophied rat hearts display an increase in antioxidant enzyme activities and because hypoxia-reoxygenation injury is known to involve free radicals, we tested the hypothesis that the hypertrophied heart may be more resistant to this type of injury. Hypertrophied rat hearts after 10 weeks of chronic pressure overload showed elevated superoxide dismutase (SOD) and glutathione peroxidase (GSHPx) activities and a decrease in lipid peroxidation as indicated by malondialdehyde (MDA) content. Glucose-free hypoxia for 15 min resulted in a complete failure of developed tension and about 200% increase in resting tension in both hypertrophied and sham control groups (p < 0.05). Upon reoxygenation for up to 30 min, hypertrophied hearts recovered developed tension to 60% and resting tension was higher by only 80% of prehypoxic values. In contrast, sham hearts showed only a 25% recovery of developed tension, whereas resting tension remained 130% higher than prehypoxic control values. During hypoxia, the SOD activity was significantly reduced in both sham and hypertrophied groups, whereas GSHPx was reduced only in the sham group. Upon reoxygenation there was no further change in these enzyme activities. Both the SOD and GSHPx activities in the hypertrophied group remained significantly higher than the corresponding reoxygenated sham hearts. During hypoxia, there was no apparent change in MDA content in either the sham or hypertrophied hearts. However, reoxygenation resulted in a significant increase in MDA content in both sham and hypertrophied hearts, but the MDA content was significantly less in the hypertrophied group (p < 0.05). It is suggested that maintenance of an adequate endogenous antioxidant reserve during hypoxia may be important in recovery upon reoxygenation.     

Exogenous GSH protection during hypoxia-reoxygenation of the isolated rat heart: impact of hypoxia duration

The objective of this study was to determine the interaction between duration of myocardial hypoxia and presence of exogenous glutathione (GSH) on functional recovery upon subsequent reoxygenation. Isolated perfused rat hearts were subjected to 20, 30, 40, or 50 min hypoxia (HYP), which resulted in a progressive decline in the amount of contractile recovery (% of normoxic rate-pressure product (RPP) and developed pressure) during 30 min reoxygenation. Supplementation with 5 mM GSH throughout normoxia, hypoxia, and reoxygenation significantly improved contractile recovery during reoxygenation after 20 and 30 min hypoxia (p < 0.05), but had no effect after longer durations of hypoxia when contractile recovery was typically below 40% of RPP and significant areas of no-reflow were observed. ECG analysis revealed that GSH shifted the bell-shaped curve for reperfusion ventricular fibrillation to the right resulting in attenuated fibrillation after 20 and 30 min hypoxia then increased incidences after 40 min when Control hearts were slow to resume electrical activity. ECG conduction velocity was well preserved in all hearts after 20 and 30 min hypoxia, but GSH administration significantly attenuated the decline that occurred with longer durations. GSH supplementation did not attenuate the 35% decline in intracellular thiols during 30 min of hypoxia. When 5 mM GSH was added only during 40 min of hypoxia, RPP recovery after reoxygenation was improved compared to unsupplemented Controls (73% vs. 55% of pre-hypoxia value, p < 0.05). Administration of GSH only during reoxygenation following 40 min of hypoxia did not alter RPP recovery compared to Control hearts. We conclude that cardioprotection by exogenous GSH is dependent on the duration of hypoxia and the functional parameter being evaluated. It is not due to an enhancement of intracellular GSH suggesting that exogenous GSH acts extracellularly to protect sarcolemmal proteins against thiol oxidation during the phase of hypoxia when oxidative stress is a major contributor to cardiac dysfunction. Furthermore, if enough damage accrues during oxygen deprivation, supplementing with GSH during reoxygenation will not impact recovery.     

Glucose oxidation and oxygen consumption of isolated guinea pig and muskrat hearts

Glucose in Krebs-Henseleit buffer was presented to isolated Langendorff perfused muskrat and guinea pig hearts that were paced at 240 beats/min. Glucose uptake (amount removed from the perfusion fluid) was 3 times greater in the muskrat hearts than in the guinea pig heart. Glucose oxidation (amount converted to CO2) and oxygen consumption did not differ in the hearts of the two species. When glucose is the only exogenous substrate, isolated muskrat hearts extract more glucose than guinea pig hearts but oxidize similar amounts of glucose and have a similar myocardial oxygen consumption.     

Exogenous GSH protection during hypoxia-reoxygenation of the isolated rat heart: Impact of hypoxia duration

The objective of this study was to determine the interaction between duration of myocardial hypoxia and presence of exogenous glutathione (GSH) on functional recovery upon subsequent reoxygenation. Isolated perfused rat hearts were subjected to 20, 30, 40, or 50 min hypoxia (HYP), which resulted in a progressive decline in the amount of contractile recovery (% of normoxic rate-pressure product (RPP) and developed pressure) during 30 min reoxygenation. Supplementation with 5 mM GSH throughout normoxia, hypoxia, and reoxygenation significantly improved contractile recovery during reoxygenation after 20 and 30 min hypoxia (p < 0.05), but had no effect after longer durations of hypoxia when contractile recovery was typically below 40% of RPP and significant areas of no-reflow were observed. ECG analysis revealed that GSH shifted the bell-shaped curve for reperfusion ventricular fibrillation to the right resulting in attenuated fibrillation after 20 and 30 min hypoxia then increased incidences after 40 min when Control hearts were slow to resume electrical activity. ECG conduction velocity was well preserved in all hearts after 20 and 30 min hypoxia, but GSH administration significantly attenuated the decline that occurred with longer durations. GSH supplementation did not attenuate the 35% decline in intracellular thiols during 30 min of hypoxia. When 5 mM GSH was added only during 40 min of hypoxia, RPP recovery after reoxygenation was improved compared to unsupplemented Controls (73% vs. 55% of pre-hypoxia value, p < 0.05). Administration of GSH only during reoxygenation following 40 min of hypoxia did not alter RPP recovery compared to Control hearts. We conclude that cardioprotection by exogenous GSH is dependent on the duration of hypoxia and the functional parameter being evaluated. It is not due to an enhancement of intracellular GSH suggesting that exogenous GSH acts extracellularly to protect sarcolemmal proteins against thiol oxidation during the phase of hypoxia when oxidative stress is a major contributor to cardiac dysfunction. Furthermore, if enough damage accrues during oxygen deprivation, supplementing with GSH during reoxygenation will not impact recovery.     

Phosphodiesterase-5 inhibition mimics intermittent reoxygenation and improves cardioprotection in the hypoxic myocardium

Although chronic hypoxia is a claimed myocardial risk factor reducing tolerance to ischemia/reperfusion (I/R), intermittent reoxygenation has beneficial effects and enhances heart tolerance to I/R. Aim of the study: To test the hypothesis that, by mimicking intermittent reoxygenation, selective inhibition of phosphodiesterase-5 activity improves ischemia tolerance during hypoxia. Adult male Sprague-Dawley rats were exposed to hypoxia for 15 days (10% O₂) and treated with placebo, sildenafil (1.4 mg/kg/day, i. p.), intermittent reoxygenation (1 h/day exposure to room air) or both. Controls were normoxic hearts. To assess tolerance to I/R all hearts were subjected to 30-min regional ischemia by left anterior descending coronary artery ligation followed by 3 h-reperfusion. Whereas hypoxia depressed tolerance to I/R, both sildenafil and intermittent reoxygenation reduced the infarct size without exhibiting cumulative effects. The changes in myocardial cGMP, apoptosis (DNA fragmentation), caspase-3 activity (alternative marker for cardiomyocyte apoptosis), eNOS phosphorylation and Akt activity paralleled the changes in cardioprotection. However, the level of plasma nitrates and nitrites was higher in the sildenafil+intermittent reoxygenation than sildenafil and intermittent reoxygenation groups, whereas total eNOS and Akt proteins were unchanged throughout. Conclusions: Sildenafil administration has the potential to mimic the cardioprotective effects led by intermittent reoxygenation, thereby opening the possibility to treat patients unable to be reoxygenated through a pharmacological modulation of NO-dependent mechanisms.     

Vascular actions of thrombin receptor peptide.

We have examined the action of the thrombin receptor-derived polypeptide, S42FLLRNPNDKYEPF55 (TRP 42-55), in rat and guinea pig aortic rings and helical arterial strips, and we have compared the actions of the peptide with those of thrombin. In rat preparations, both TRP 42-55 and thrombin caused a concentration-dependent endothelium-dependent relaxation that was blocked by N omega-nitro-L-arginine methyl ester; the relaxation response of the intact rat aortic strip preparation to concentrations of the peptide in the range 30-60 micrograms/mL (17-34 microM) was equivalent to the response to 0.03-0.1 U/mL of thrombin (about 0.3-0.9 nM), yielding a potency ratio (TRP 42-55:thrombin) of about 38,000:1. In contrast with the complete desensitization of thrombin-treated rat aortic preparations to a second administration of the enzyme, the rat aortic tissue was not desensitized by repeated exposures to TRP 42-55 and remained responsive to the peptide even after treatment of the tissue by thrombin. In contrast with the rat aortic tissue, in either intact or endothelium-free guinea pig aortic preparations both TRP 42-55 and thrombin caused a concentration-dependent endothelium-independent contraction. The contractile action of 60 micrograms/mL of receptor peptide (34 microM) in guinea pig aortic strip preparations was equivalent to the contractile action of 0.1-0.3 U/mL thrombin (0.9-3 nM), yielding a potency ratio of about 17,000:1. In guinea pig aortic preparations with an intact endothelium that were precontracted with noradrenaline, neither thrombin nor TRP42-55 caused relaxation, whereas substance P did so.(ABSTRACT TRUNCATED AT 250 WORDS)     

丹参对心肌低氧/复氧损伤的保护作用的研究

目的：研究中药丹参（ＳＭ）对心肌低氧／复氧损伤的保护作用。方法：运用＾３１Ｐ－ＮＭＲ技术对离体灌流大鼠心脏的高能磷酸化合物含量及细胞内的ｐＨ值（ｐＨｉ）进行动态跟踪。结果：丹参注射液能明显减轻低氧期间心肌高能磷酸合物含量的下降,促使复氧期间ＰＣｒ、ＡＴＰ相对含量的恢复,减少低氧及复氧阶段心肌ｐＨｉ的下降。结论：丹参参改善低氧及复氧期间心肌能量代谢水平,减轻心肌低氧／复氧损伤,并能显著改善细胞内酸碱     

Effect of thymol on calcium handling in mammalian ventricular myocardium

Concentration-dependent effects of thymol on calcium handling were studied in canine and guinea pig cardiac preparations (Langendorff-perfused guinea pig hearts, canine ventricular trabeculae, canine sarcoplasmic reticular vesicles and single ryanodine receptors). Thymol induced a concentration-dependent negative inotropic action in both canine and guinea pig preparations (EC(50) = 297 +/- 12 microM in dog). However, low concentrations of thymol reduced intracellular calcium transients in guinea pig hearts without decreasing contractility. At higher concentrations both calcium transients and contractions were suppressed. In canine sarcoplasmic reticular vesicles thymol induced rapid release of calcium (V(max) = 0.47 +/- 0.04 nmol s(-1), EC(50) = 258 +/- 21 microM, Hill coefficient = 3.0 +/- 0.54), and decreased the activity of the calcium pump (EC(50) = 253 +/- 4.7 microM, Hill coefficient = 1.62 +/- 0.05). Due to the less sharp concentration-dependence of the ATPase inhibition, this effect was significant from 50 microM, whereas the thymol-induced calcium release only from 100 microM. In single ryanodine receptors incorporated into artificial lipid bilayer thymol induced long lasting openings, having mean open times increased with 3 orders of magnitude, however, the specific conductance of the channel remained unaltered. This effect of thymol was not voltage-dependent and failed to prevent the binding of ryanodine. In conclusion, the negative inotropic action of thymol can be explained by reduction in calcium content of the sarcoplasmic reticulum due to the combination of the thymol-induced calcium release and inhibition of the calcium pump. The calcium-sensitizer effect, observed at lower thymol concentrations, indicates that thymol is likely to interact with the contractile machinery also.     

Pituitary adenylate cyclase-activating polypeptide: localization and differential influence on isolated hearts from rats and guinea pigs

This study was done to determine if pituitary adenylate cyclase-activating peptide (PACAP)-immunoreactive nerve fibers occur in cardiac muscle as well as intracardiac ganglia of rats and guinea pigs and to clarify the chronotropic actions of PACAP27 in the same species using isolated heart preparations. PACAP nerve fibers were not detected in atrial or ventricular muscle of rat or guinea pig but a few stained nerve fibers occurred in the atrioventricular bundle of the guinea pig. Stained nerve fibers were prominent in intracardiac ganglia of both species. PACAP27 caused a dose-dependent tachycardia in isolated rat hearts (+39 +/- 3 beats/min with 1 nmol, n = 6). Positive and/or negative chronotropic responses were evoked by PACAP27 in guinea pig heart, depending on dose and prior exposure to the peptide. PACAP27 also caused arrhythmias in several guinea pig hearts. Treatment with atropine eliminated or prevented PACAP-evoked bradycardia and arrhythmias, implicating cholinergic neurons in these responses. Positive chronotropic responses to PACAP were unaffected by beta-adrenergic receptor blockade in either species, suggesting that tachycardia resulted from a direct action on the heart. These observations support the conclusion that endogenous PACAP could have a role in regulating parasympathetic input to the heart but through different mechanisms in rats versus guinea pigs. A direct positive chronotropic influence of endogenous PACAP is unlikely since atrial muscle lacks PACAP-immunoreactive nerve fibers.     

Effects of the ionophore grisorixin on myocardial function and metabolism in isolated perfused working rat heart under normoxic and hypoxic conditions

The effects of grisorixin, a monocarboxylic ionophore, were studied on isolated working rat hearts perfused with a suspension of washed pig erythrocytes (10% hematocrit). Grisorixin (2.5 microM) induced a transient stimulation of heart work, maximal at 5 min, expressed by an increase in heart rate (+21%) and aortic flow (+17%) and by an increase in coronary flow, maximal at 10 min (+47%). Concomitantly, myocardial Vo2 was slightly enhanced and the myocardial creatine phosphate level dropped (2 min). The lactate production increased by 82% (5 min) then dropped to the control value (10 min) and increased again till the 45th min (+211%), indicating a cardiac metabolic drift towards anaerobic glycolysis due to partial inhibition of the oxidative metabolism. Owing to its properties as an ionophore, grisorixin also induced a strong and rapid increase of potassium concentration in the perfusate and a decrease of sodium. Grisorixin was tested on hearts submitted to 20 min of hypoxic conditions. The hypoxia was rather mild and induced only very slight modifications of the ultrastructure. In the control series, heart rate and aortic flow decreased regularly while coronary flow and lactate production increased. Upon reoxygenation, the heart performances were rapidly restored. Grisorixin was administered according to four different protocols. When injected at the onset of hypoxia or 5 min later, it was able to maintain the aortic flow during the first minutes and induce a higher coronary dilation. These beneficial effects were short-lasting and no deleterious effects were found on the ultrastructure of hearts subjected to grisorixin whether after hypoxia or after reoxygenation.     

线粒体钾通道参与葛根素抗心肌细胞缺氧/复氧损伤的作用

目的:探讨线粒体ATP敏感性钾通道和线粒体钙激活钾通道在葛根素预处理抗心肌细胞缺氧/复氧损伤中的作用。方法:采用酶解分离大鼠心肌细胞复制心肌细胞缺氧/复氧模型,台盼蓝拒染法测定心肌细胞存活率;四甲基罗丹明乙酯(TMRE)孵育测定线粒体膜电位值;分离线粒体测定线粒体渗透性转换孔开放程度。结果:与缺氧/复氧组相比,葛根素(0.24mmol/L)预处理5min可明显增加心肌细胞的存活率,线粒体ATP敏感性钾通道抑制剂5-羟基癸酸(100μmol/L,预处理20min)或线粒体钙激活钾通道阻断剂paxilline(1μmol/L,预处理5min)均可拮抗葛根素的作用。葛根素预处理可明显减弱缺氧引起的线粒体膜电位的耗损,5-羟基癸酸和paxilline都能明显拮抗其作用。在分离心肌线粒体模型上,葛根素显著减弱CaCl2诱导的线粒体在A520处吸光度降低,其作用与单独应用线粒体渗透性转换孔抑制剂环孢菌素A相似;5-羟基癸酸和paxilline可拮抗葛根素的保护作用。结论:在大鼠分离心肌细胞模型或分离线粒体模型上,葛根素预处理具有抗缺氧/复氧损伤的作用,这种保护作用可能与其促进线粒体ATP敏感性钾通道和线粒体钙激活钾通道的开放,进而稳定线粒体膜电位,抑制线粒体渗透性转换孔开放有关。