Anesthetic preconditioning decreases arrhythmias and improves regional conduction in isolated hearts.

OBJECTIVE: Anesthetic preconditioning (APC) is known to protect the heart against necrosis and contractile dysfunction, but protection against arrhythmias has not been well characterized. The authors hypothesized that APC alters the dispersion of electrophysiologic parameters to reduce arrhythmias after global (G) or regional (R) ischemia. DESIGN: Prospective vehicle-controlled study. SETTING: A university research laboratory. SUBJECTS: Langendorff rat hearts (n = 66). INTERVENTIONS: The authors examined the occurrence of arrhythmias, their mean duration, and the magnitude-squared coherence (MSC) of spectral components that provide a quantitative measure of rhythm organization at multiple sites in the heart, expressed as a function of time. Six groups received 0.5 minimum alveolar concentration (MAC) (APC-G, 0.5; APC-R, 0.5, respectively; 0.17 +/- 0.01 mmol/L and 0.18 +/- 0.05 mmol/L) or 1 MAC of isoflurane (APC-G 1.0; APC-R 1.0, respectively, 0.28 +/- 0.02 mmol/L and 0.31 +/- 0.05 mmol/L) before 30 minutes of global (ISC-G) or regional ischemia (ISC-R). Another group (SHAM) was neither subjected to ischemia nor isoflurane. MEASUREMENTS AND MAIN RESULTS: Electrodes were placed on the right atrium, the base, and the apex of the right ventricle. The incidence of ventricular fibrillation (VF) was as follows: ISC-G, 100%; APC-G 0.5, 50%; APC-G 1.0, 40%; ISC-R, 100%; APC-R 0.5, 50%; APC-R 1.0, 50% compared with SHAM 0%. Isoflurane-treated hearts showed delayed onset and decreased duration of arrhythmias on reperfusion. Untreated hearts showed low levels of MSC during reperfusion. In contrast, the isoflurane-treated hearts exhibited moderate-to-high levels of MSC during reperfusion. CONCLUSION: APC reduces the incidence of arrhythmia after global and regional ischemia. In addition, the temporal synchrony of conduction is increased, suggesting a more organized pattern of excitation.

Reactive oxygen species as mediators of cardiac injury and protection: the relevance to anesthesia practice.

Reactive oxygen species (ROS) are central to cardiac ischemic and reperfusion injury. They contribute to myocardial stunning, infarction and apoptosis, and possibly to the genesis of arrhythmias. Multiple laboratory studies and clinical trials have evaluated the use of scavengers of ROS to protect the heart from the effects of ischemia and reperfusion. Generally, studies in animal models have shown such effects. Clinical trials have also shown protective effects of scavengers, but whether this protection confers meaningful clinical benefits is uncertain. Several IV anesthetic drugs act as ROS scavengers. In contrast, volatile anesthetics have recently been demonstrated to generate ROS in the heart, most likely because of inhibitory effects on cardiac mitochondria. ROS are involved in the signaling cascade for cardioprotection induced by brief exposure to a volatile anesthetic (termed "anesthetic preconditioning"). ROS, therefore, although injurious in large quantities, can have a paradoxical protective effect within the heart. In this review we provide background information on ROS formation and elimination relevant to anesthetic and adjuvant drugs with particular reference to the heart. The sources of ROS, the means by which they induce cardiac injury or activate protective signaling pathways, the results of clinical studies evaluating ROS scavengers, and the effects of anesthetic drugs on ROS are each discussed.

Anesthetic preconditioning: the role of free radicals in sevoflurane-induced attenuation of mitochondrial electron transport in Guinea pig isolated hearts.

Cardioprotection by anesthetic preconditioning (APC) can be abolished by nitric oxide (NO*) synthase inhibitors or by reactive oxygen species (ROS) scavengers. We previously reported attenuated mitochondrial electron transport (ET) and increased ROS generation during preconditioning sevoflurane exposure as part of the triggering mechanism of APC. We hypothesized that NO* and other ROS mediate anesthetic-induced ET attenuation. Cardiac function and reduced nicotinamide adenine dinucleotide (NADH) fluorescence, an index of mitochondrial ET, were measured online in 68 Langendorff-prepared guinea pig hearts. Hearts underwent 30 min of global ischemia and 120 min of reperfusion. Before ischemia, hearts were temporarily perfused with superoxide dismutase, catalase, and glutathione to scavenge ROS or N(G)-nitro-L-arginine-methyl-ester (L-NAME) to inhibit NO* synthase in the presence or absence of 1.3 mM sevoflurane (APC). APC temporarily increased NADH before ischemia, i.e., it attenuated mitochondrial ET. Both this NADH increase and the cardioprotection by APC on reperfusion were prevented by superoxide dismutase, catalase, and glutathione and by N(G)-nitro-L-arginine-methyl-ester. Thus, ROS and NO*, or reaction products including peroxynitrite, mediate sevoflurane-induced ET attenuation. This may lead to a positive feedback mechanism with augmented ROS generation to trigger APC secondary to altered mitochondrial function.

Ocular microtremor during general anesthesia: results of a multicenter trial using automated signal analysis.

Ocular microtremor (OMT) is a fine physiologic tremor of the eye related to neuronal activity in the reticular formation of the brainstem. The frequency of OMT is suppressed by propofol and sevoflurane and predicts the response to command at emergence from anesthesia. Previous studies have relied on post hoc computer analysis of OMT wave forms or on real-time measurements confirmed visually on an oscilloscope. Our overall aim was to evaluate an automated system of OMT signal analysis in a diverse patient population undergoing general anesthesia. In a multicenter trial involving four centers in three countries, we examined the accuracy of OMT to identify the unconscious state and to predict movement in response to airway instrumentation and surgical stimulation. We also tested the effects of neuromuscular blockade and patient position on OMT. We measured OMT continuously by using the closed-eye piezoelectric technique in 214 patients undergoing extracranial surgery with general anesthesia using a variety of anesthetics. OMT decreased at induction in all patients, increased transiently in response to surgical incision or airway instrumentation, and increased at emergence. The frequency of OMT predicted movement in response to laryngeal mask airway insertion and response to command at emergence. Neuromuscular blockade did not affect the frequency of OMT but decreased its amplitude. OMT frequency was unaffected by changes in patient position. We conclude that OMT, measured by an automated signal analysis module, accurately determines the anesthetic state in surgical patients, even during profound neuromuscular blockade and after changes in patient position.

Attenuation of mitochondrial respiration by sevoflurane in isolated cardiac mitochondria is mediated in part by reactive oxygen species.

BACKGROUND: Anesthetic preconditioning protects against cardiac ischemia/reperfusion injury. Increases in reduced nicotinamide adenine dinucleotide and reactive oxygen species during sevoflurane exposure suggest attenuated mitochondrial electron transport as a trigger of anesthetic preconditioning. The authors investigated the effects of sevoflurane on respiration in isolated cardiac mitochondria. METHODS: Mitochondria were isolated from fresh guinea pig hearts, and mitochondrial oxygen consumption was measured in the presence of complex I (pyruvate) or complex II (succinate) substrates. The mitochondria were exposed to 0, 0.13, 0.39, 1.3, or 3.9 mM sevoflurane. State 3 respiration was determined after adenosine diphosphate addition. The reactive oxygen species scavengers manganese(III) tetrakis (4-benzoic acid) porphyrin chloride and N-tert-Butyl-a-(2-sulfophenyl)nitrone sodium (10 microM each), or the K(ATP) channel blockers glibenclamide (2 microM) or 5-hydroxydecanoate (300 microM), were given alone or before 1.3 mM sevoflurane. RESULTS: Sevoflurane attenuated respiration for both complex I and complex II substrates, depending on the dose. Glibenclamide and 5-hydroxydecanoate had no effect on this attenuation. Both scavengers, however, abolished the sevoflurane-induced attenuation for complex I substrates, but not for complex II substrates. CONCLUSION: The findings suggest that sevoflurane-induced attenuation of complex I is mediated by reactive oxygen species, whereas attenuation of other respiratory complexes is mediated by a different mechanism. The opening of mitochondrial K(ATP) channels by sevoflurane does not seem to be involved in this effect. Thus, reactive oxygen species formation may not only result from attenuated electron transport by sevoflurane, but it may also contribute to complex I attenuation, possibly leading to a positive feedback and amplification of sevoflurane-induced reactive oxygen species formation in triggering anesthetic preconditioning.

Dual exposure to sevoflurane improves anesthetic preconditioning in intact hearts.

BACKGROUND: Anesthetic preconditioning (APC) with sevoflurane reduces myocardial ischemia-reperfusion injury. The authors tested whether two brief exposures to sevoflurane would lead to a better preconditioning state than would a single longer exposure and whether dual exposure to a lower (L) concentration of sevoflurane would achieve an outcome similar to that associated with a single exposure to a higher (H) concentration. METHODS: Langendorff-prepared guinea pig hearts were exposed to 0.4 mM sevoflurane once for 15 min (H1-15; n = 8) or 0.4 mM (H2-5; n = 8) or 0.2 mM sevoflurane (L2-5; n = 8) twice for 5 min, with a 5-min washout period interspersed. Sevoflurane was then washed out for 20 min before 30 min of global no-flow ischemia and 120 min of reperfusion. Control hearts (n = 8) were not subjected to APC. Left ventricular pressure was measured isovolumetrically. Ventricular infarct size was determined by tetrazolium staining and cumulative planimetry. Values are expressed as mean +/- SD. RESULTS: The authors found a better functional return and a lesser percentage of infarction on reperfusion in H2-5 (28 +/- 9%) than in H1-15 (36 +/- 8%; P < 0.05), L2-5 (43 +/- 6%; P < 0.05), or control hearts (52 +/- 7%; P < 0.05). CONCLUSION: These results suggest that APC depends not only on the concentration but also on the protocol used for preconditioning. Similarly to ischemic preconditioning, repeated application of the volatile anesthetic seems to be more important than the duration of exposure in initiating the signaling sequence that elicits APC at clinically relevant concentrations. Therefore, repeated cycles of anesthetic exposure followed by volatile anesthetic-free periods may be beneficial for APC in the clinical setting.

Cardiac preconditioning by volatile anesthetic agents: a defining role for altered mitochondrial bioenergetics.

Volatile anesthetic agents, such as halothane, isoflurane, and sevoflurane, are the drugs most commonly used to maintain the state of general anesthesia. They have long been known to provide some protection against the effects of cardiac ischemia and reperfusion. Several mechanisms likely contribute to this cardioprotection, including coronary vasodilation, reduced contractility with corresponding decreased metabolic demand, and a direct effect to decrease myocardial Ca(2+) entry through L-type Ca(2+) channels. Recently, a memory phase to cardioprotection has been observed by these agents, which is inhibited by ATP-sensitive potassium channel inhibition. These features suggest a pathway that shares components with those required for ischemic preconditioning, despite the remarkable differences between these two stimuli, and the term anesthetic preconditioning (APC) has been adopted. Scavengers of reactive oxygen species (ROS) abrogate APC, suggesting an effect of anesthetic agents to cause ROS formation. Such an effect has recently been directly demonstrated. The mechanism by which these drugs induce ROS formation is unclear. However, direct inhibition of mitochondrial electron transport system enzymes, and altered mitochondrial bioeneregtics in hearts preconditioned by volatile anesthetics, strongly implicate the mitochondria as the target for these effects. Furthermore, decreased mitochondrial ROS formation during ischemia and reperfusion in hearts preconditioned by volatile anesthetics might underlie the improved postischemic structure and function. APC presents a safe mode to apply preconditioning to human hearts. This review summarizes the major developments in a field that is exciting to clinicians and basic scientists alike.

Reduced reactive O2 species formation and preserved mitochondrial NADH and [Ca2+] levels during short-term 17 degrees C ischemia in intact hearts.

OBJECTIVE: Different cardioprotective strategies such as ischemic or pharmacologic preconditioning lead to attenuated ischemia/reperfusion (I/R) injury with less mechanical dysfunction and reduced infarct size on reperfusion. Improved mitochondrial function during ischemia as well as on reperfusion is a key feature of cardioprotection. The best reversible cardioprotective strategy is hypothermia. We investigated mitochondrial protection before, during, and after hypothermic ischemia by measuring mitochondrial (m)Ca2+, NADH, and reactive oxygen species (ROS) by online spectrophotofluorometry in intact hearts. METHODS: A fiberoptic cable was placed against the left ventricle of Langendorff-prepared guinea pig hearts to excite and record transmyocardial fluorescence at the appropriate wavelengths during 37 and 17 degrees C perfusion and during 30 min ischemia at 37 and 17 degrees C before 120 min reperfusion/rewarming. RESULTS: Cold perfusion caused significant reversible increases in m[Ca2+], NADH, and ROS. Hypothermia prevented a further increase in m[Ca2+], excess ROS formation and NADH oxidation/reduction imbalance during ischemia, led to a rapid return to preischemic values on warm reperfusion, and preserved cardiac function and tissue viability on reperfusion. CONCLUSIONS: Hypothermic perfusion at 17 degrees C caused moderate and reversible changes in mitochondrial function. However, hypothermia protects during ischemia, as shown by preservation of mitochondrial NADH energy balance and prevention of deleterious increases in m[Ca2+] and ROS formation. The close temporal relations of these factors during cooling and during ischemia suggest a causal link between mCa2+, mitochondrial energy balance, and ROS production.

Hypothermia augments reactive oxygen species detected in the guinea pig isolated perfused heart.

Hypothermic perfusion of the heart decreases oxidative phosphorylation and increases NADH. Because O(2) and substrates remain available and respiration (electron transport system, ETS) may become impaired, we examined whether reactive oxygen species (ROS) exist in excess during hypothermic perfusion. A fiberoptic probe was placed on the left ventricular free wall of isolated guinea pig hearts to record intracellular ROS, principally superoxide (O(2)(-).), and an extracellular reactive nitrogen reactant, principally peroxynitrite (ONOO(-)), a product of nitric oxide (NO.) + O(2)(-). Hearts were loaded with dihydroethidium (DHE), which is oxidized by O(2)(-). to ethidium, or were perfused with l-tyrosine, which is oxidized by ONOO(-) to dityrosine (diTyr). Shifts in fluorescence were measured online; diTyr fluorescence was also measured in the coronary effluent. To validate our methods and to examine the source and identity of ROS during cold perfusion, we examined the effects of a superoxide dismutase mimetic Mn(III) tetrakis(4-benzoic acid)porphyrin chloride (MnTBAP), the nitric oxide synthase inhibitor N(G)-nitro-l-arginine methyl ester (l-NAME), and several agents that impair electron flux through the ETS: menadione, sodium azide (NaN(3)), and 2,3-butanedione monoxime (BDM). Drugs were given before or during cold perfusion. ROS measured by DHE was inversely proportional to the temperature between 37 degrees C and 3 degrees C. We found that perfusion at 17 degrees C increased DHE threefold versus perfusion at 37 degrees C; this was reversed by MnTBAP, but not by l-NAME or BDM, and was markedly augmented by menadione and NaN(3). Perfusion at 17 degrees C also increased myocardial and effluent diTyr (ONOO(-)) by twofold. l-NAME, MnTBAP, or BDM perfused at 37 degrees C before cooling or during 17 degrees C perfusion abrogated, whereas menadione and NaN(3) again enhanced the cold-induced increase in ROS. Our results suggest that hypothermia moderately enhances O(2)(-). generation by mitochondria, whereas O(2)(-). dismutation is markedly slowed. Also, the increase in O(2)(-). during hypothermia reacts with available NO. to produce ONOO(-), and drug-induced O(2)(-). dismutation eliminates the hypothermia-induced increase in O(2)(-).

Ischemic preconditioning: triggering role of nitric oxide-derived oxidants in isolated hearts.

There is evidence that oxidants generated during ischemic preconditioning (IPC) trigger or mediate cardioprotection. We examined whether a causal relationship exists between oxidant formation during ischemic preconditioning and cardioprotection. We monitored formation of dityrosine in crystalloid-perfused guinea pig isolated hearts after a preconditioning protocol and after prolonged ischemia. Superoxide dismutase, catalase, and glutathione (SCG), or the L-arginine analogue NGnitro L-arginine methyl ester (L-NAME) were given during preconditioning. Dityrosine was observed in the coronary effluent immediately after both stimuli, but not after bracketing with SCG or L-NAME. After prolonged ischemia, dityrosine was significantly lower in the IPC group than in other groups. IPC was evidenced by improved mechanical and metabolic function on reperfusion, and by reduced infarction. These effects were abrogated by either SCG or L-NAME. These data support the hypothesis that the formation of nitric oxide-derived oxidants during ischemic preconditioning is causally related to myocardial adaptation to reperfusion injury.

Anesthetic preconditioning: effects on latency to ischemic injury in isolated hearts.

BACKGROUND: Anesthetic preconditioning (APC) is protective for several aspects of cardiac function and structure, including left ventricular pressure, coronary flow, and infarction. APC may be protective, however, only if the duration of ischemia is within a certain, as yet undefined range. Brief ischemia causes minimal injury, and APC would be expected to provide little benefit. Conversely, very prolonged ischemia would ultimately cause serious injury with or without APC. Previous investigations used a constant ischemic time as the independent variable to assess ischemia-induced changes in dependent functional and structural variables. The purpose of the study was to define the critical limits of efficacy of APC by varying ischemic time. METHODS: Guinea pig hearts (Langendorff preparation; n = 96) underwent pretreatment with sevoflurane (APC) or no treatment (control), before global ischemia and 120 min reperfusion. Ischemia durations were 20, 25, 30, 35, 40, and 45 min. RESULTS: At 120 min reperfusion, developed (systolic-diastolic) left ventricular pressure was increased by APC compared with control for ischemia durations of 25-40 min. Infarction was decreased by APC for ischemia durations of 25-40 min, but not 20 or 45 min. APC improved coronary flow and vasodilator responses for all ischemia durations longer than 25 min, and decreased ventricular fibrillation on reperfusion for ischemia durations longer than 30 min. CONCLUSIONS: Although APC protects against vascular dysfunction and dysrhythmias after prolonged ischemia, protection against contractile dysfunction and infarction in this model is restricted to a range of ischemia durations of 25-40 min. These results suggest that APC may be effective in a subset of patients who have cardiac ischemia of intermediate duration.

Reactive oxygen species precede the epsilon isoform of protein kinase C in the anesthetic preconditioning signaling cascade.

BACKGROUND: Protein kinase C (PKC) and reactive oxygen species (ROS) are known to have a role in anesthetic preconditioning (APC). Cardiac preconditioning by triggers other than volatile anesthetics, such as opioids or brief ischemia, is known to be isoform selective, but the isoform required for APC is not known. The authors aimed to identify the PKC isoform that is involved in APC and to elucidate the relative positions of PKC activation and ROS formation in the APC signaling cascade. METHODS: Isolated guinea pig hearts were subjected to 30 min of ischemia and 120 min of reperfusion. Before ischemia, hearts were either untreated or treated with sevoflurane (APC) in the absence or presence of the nonspecific PKC inhibitor chelerythrine, the PKC-delta inhibitor PP101, or the PKC-epsilon inhibitor PP149. Spectrofluorometry and the fluorescent probes dihydroethidium were used to measure intracellular ROS, and effluent dityrosine as used to measure extracellular ROS release. RESULTS: Previous sevoflurane exposure protected the heart against ischemia-reperfusion injury, as previously described. Chelerythrine or PP149 abolished protection, but PP101 did not. ROS formation was observed during sevoflurane exposure and was not altered by any of the PKC inhibitors. CONCLUSIONS: APC is mediated by PKC-epsilon but not by PKC-delta. Furthermore, PKC activation probably occurs downstream of ROS generation in the APC signaling cascade.

Anesthetic preconditioning improves adenosine triphosphate synthesis and reduces reactive oxygen species formation in mitochondria after ischemia by a redox dependent mechanism.

BACKGROUND: Mitochondrial changes that characterize the heart after anesthetic preconditioning (APC) or the mechanisms by which mitochondrial triggering factors lead to protection are unknown. This study hypothesized that generation of reactive oxygen species (ROS) during APC is required to initiate the mitochondrial protective effects, and that APC leads to improved mitochondrial electron transport chain function and cardiac function during reperfusion. METHODS: Isolated guinea pig hearts were subject to 30 min ischemia and 120 min reperfusion. Prior to ischemia hearts were either untreated (I/R), or treated with sevoflurane (APC), in the presence or absence of the ROS scavenger tiron (TIR), or the superoxide dismutase mimetic MnTBAP (TBAP). Intracellular ROS were measured by spectrofluorometry using the fluorescent probe dihydroethidium (DHE). In another series of experiments, using the same protocol, hearts were reperfused for only 5 min and removed for measurement of adenosine triphosphate (ATP) synthesis by luciferin-luciferase luminometry and ROS generation by dichlorohydro-fluorescein (DCF) fluorescence in isolated mitochondria. RESULTS: The APC improved cardiac function and reduced infarction. Tiron or MnTBAP abrogated the protection afforded by APC. Mitochondrial ATP synthesis was decreased by 70 +/- 3% after IR alone, by only 7 +/- 3% after APC, by 69 +/- 2% after APC+TIR, and by 71 +/- 3% after APC + TBAP. Mitochondrial ROS formation (DCF) increased by 48 +/- 3% after IR alone, by 0 +/- 2% after APC, by 43 +/- 4% after APC + TIR, and by 46 +/- 3% after APC + TBAP. ROS generation (DHE) was increased in I/R group at 5 and 120 min reperfusion. This was attenuated by APC but this protective effect was abrogated in APC + TIR and APC + TBAP groups. CONCLUSIONS: The results indicate that ROS are central both in triggering and mediating APC, and that the mitochondrion is the target for these changes.

Sevoflurane exposure generates superoxide but leads to decreased superoxide during ischemia and reperfusion in isolated hearts.

UNLABELLED: Reactive oxygen species (ROS) are largely responsible for cardiac injury consequent to ischemia and reperfusion, but, paradoxically, there is evidence suggesting that anesthetics induce preconditioning (APC) by generating ROS. We hypothesized that sevoflurane generates the ROS superoxide (O(2)(.-)), that APC attenuates O(2)(.-) formation during ischemia, and that this attenuation is reversed by bracketing APC with the O(2)(.-) scavenger manganese (III) tetrakis (4-benzoic acid) porphyrin chloride (MnTBAP) or the putative mitochondrial adenosine triphosphate-sensitive potassium (mK(ATP)) channel blocker 5-hydroxydecanoate (5-HD). O(2)(.-) was measured continuously in guinea pig hearts by using dihydroethidium. Sevoflurane was administered alone (APC), with MnTBAP, or with 5-HD before 30 min of ischemia and 120 min of reperfusion. Control hearts underwent no pretreatment. Sevoflurane directly increased O(2)(.-); this was blocked by MnTBAP but not by 5-HD. O(2)(.-) increased during ischemia and during reperfusion. These increases in O(2)(.-) were attenuated in the APC group, but this was prevented by MnTBAP or 5-HD. We conclude that sevoflurane directly induces O(2)(.-) formation but that O(2)(.-) formation is decreased during subsequent ischemia and reperfusion. The former effect appears independent of mK(ATP) channels, but not the latter. Our study indicates that APC is initiated by ROS that in turn cause mK(ATP) channel opening. Although there appears to be a paradoxical role for ROS in triggering and mediating APC, a possible mechanism is offered. IMPLICATIONS: Reactive oxygen species (ROS) are implicated in triggering anesthetic preconditioning (APC). The ROS superoxide (O(2)(.-)) was measured continuously in guinea pig isolated hearts. Sevoflurane directly increased O(2)(.-) but led to attenuated O(2)(.-) formation during ischemia. This demonstrates triggering of APC by ROS and clarifies the mechanism of cardioprotection during ischemia.

Cross-bridge kinetics modeled from myoplasmic [Ca2+] and LV pressure at 17 degrees C and after 37 degrees C and 17 degrees C ischemia.

We modeled changes in contractile element kinetics derived from the cyclic relationship between myoplasmic [Ca(2+)], measured by indo 1 fluorescence, and left ventricular pressure (LVP). We estimated model rate constants of the Ca(2+) affinity for troponin C (TnC) on actin (A) filament (TnCA) and actin and myosin (M) cross-bridge (A x M) cycling in intact guinea pig hearts during baseline 37 degrees C perfusion and evaluated changes at 1) 20 min 17 degrees C pressure, 2) 30-min reperfusion (RP) after 30-min 37 degrees C global ischemia during 37 degrees C RP, and 3) 30-min RP after 240-min 17 degrees C global ischemia during 37 degrees C RP. At 17 degrees C perfusion versus 37 degrees C perfusion, the model predicted: A x M binding was less sensitive; A x M dissociation was slower; Ca(2+) was less likely to bind to TnCA with A x M present; and Ca(2+) and TnCA binding was less sensitive in the absence of A x M. Model results were consistent with a cold-induced fall in heart rate from 260 beats/min (37 degrees C) to 33 beats/min (17 degrees C), increased diastolic LVP, and increased phasic Ca(2+). On RP after 37 degrees C ischemia vs. 37 degrees C perfusion, the model predicted the following: A x M binding was less sensitive; A x M dissociation was slower; and Ca(2+) was less likely to bind to TnCA in the absence of A. M. Model results were consistent with reduced myofilament responsiveness to [Ca(2+)] and diastolic contracture on 37 degrees C RP. In contrast, after cold ischemia versus 37 degrees C perfusion, A x M association and dissociation rates, and Ca(2+) and TnCA association rates, returned to preischemic values, whereas the dissociation rate of Ca(2+) from A x M was ninefold faster. This cardiac muscle kinetic model predicted a better-restored relationship between Ca(2+) and cross-bridge function on RP after an eightfold longer period of 17 degrees C than 37 degrees C ischemia.

Ischemic preconditioning alters real-time measure of O2 radicals in intact hearts with ischemia and reperfusion.

Reactive oxygen species (ROS) are believed to be involved in triggering cardiac ischemic preconditioning (IPC). Decreased formation of ROS on reperfusion after prolonged ischemia may in part underlie protection by IPC. In heart models, these contentions have been based either on the effect of ROS scavengers to abrogate IPC-induced preservation or on a measurement of oxidation products on reperfusion. Using spectrophotofluorometry at the left ventricular wall and the fluorescent probe dihydroethidium (DHE), we measured intracellular ROS superoxide (O(2)(-).) continuously in isolated guinea pig heart and tested the effect of IPC and the O(2)(-). scavenger manganese(III) tetrakis (4-benzoic acid) porphyrin chloride (MnTBAP) on O(2)(-). formation throughout the phases of preconditioning (PC), 30-min ischemia and 60-min reperfusion (I/R). IPC was evidenced by improved contractile function and reduced infarction; MnTBAP abrogated these effects. Brief PC pulses increased O(2)(-). during the ischemic but not the reperfusion phase. O(2)(-). increased by 35% within 1 min of ischemia, increased further to 95% after 20 min of ischemia, and decreased slowly on reperfusion. In the IPC group, O(2)(-). was not elevated over 35% during index ischemia and was not increased at all on reperfusion; these effects were abrogated by MnTBAP. Our results directly demonstrate how intracellular ROS increase in intact hearts during IPC and I/R and clarify the role of ROS in triggering and mediating IPC.