The role of mitochondrial and sarcolemmal K(ATP) channels in canine ethanol-induced preconditioning in vivo

Chronic consumption of small doses of ethanol protects myocardium from ischemic injury. We tested the hypothesis that mitochondrial and sarcolemmal adenosine triphosphate-dependent potassium (K(ATP)) channels mediate these beneficial effects. Dogs (n = 76) were fed with ethanol (1.5 g/kg) or water mixed with dry food bid for 6 or 12 wk, fasted overnight before experimentation, and instrumented for measurement of hemodynamics. Dogs received intracoronary saline (vehicle), 5-hydroxydecanoate (a mitochondrial K(ATP) channel antagonist; 6.75 mg/kg over 45 min), or HMR-1098 (a sarcolemmal K(ATP) channel antagonist; 45 microg/kg over 45 min) and were subjected to a 60 min coronary artery occlusion followed by 3 h of reperfusion. A final group of dogs was pretreated with ethanol and chow for 6 wk before occlusion and reperfusion. Myocardial infarct size and transmural coronary collateral blood flow were measured with triphenyltetrazolium chloride staining and radioactive microspheres, respectively. The area at risk of infarction was similar between groups. A 12-wk pretreatment with ethanol significantly reduced infarct size to 13% +/- 2% (mean +/- SEM; n = 8) of the area at risk compared with control experiments (25% +/- 2%; n = 8), but a 6-wk pretreatment did not (21% +/- 2%; n = 8). 5-hydroxydecanoate and HMR-1098 abolished the protective effects of 12-wk ethanol pretreatment (24% +/- 2% and 29% +/- 3%, respectively; n = 8 for each group) but had no effect in dogs that did not receive ethanol (22% +/- 2% and 23% +/- 4%, respectively; n = 8 for each group). No differences in hemodynamics or transmural coronary collateral blood flow were observed between the groups. The results indicate that mitochondrial and sarcolemmal K(ATP) channels mediate ethanol-induced preconditioning in dogs independent of alterations in systemic hemodynamics or coronary collateral blood flow. IMPLICATIONS: Mitochondrial and sarcolemmal K(ATP) channels mediate ethanol-induced preconditioning independent of alterations in systemic hemodynamics or coronary collateral perfusion in vivo.     

Morphine induces preconditioning via activation of mitochondrial KCa channels

Purpose

Mitochondrial calcium sensitive potassium (mK_Ca) channels are involved in cardioprotection induced by ischemic preconditioning. In the present study we investigated whether morphine-induced preconditioning also involves activation of mK_Ca channels.

Methods

Isolated rat hearts (six groups; each n = 8) underwent global ischemia for 30 min followed by a 60-min reperfusion. Control animals were not further treated. Morphine preconditioning (MPC) was initiated by two five-minute cycles of morphine 1 μM infusion with one five-minute washout and one final ten-minute washout period before ischemia. The mK_Ca blocker, paxilline 1 μM, was administered, with and without morphine administration (MPC + Pax and Pax). As a positive control, we added an ischemic preconditioning group (IPC) alone and combined with paxilline (IPC + Pax). At the end of reperfusion, infarct sizes were determined by triphenyltetrazoliumchloride staining.

Results

Infarct size was (mean ± SD) 45 ± 9% of the area at risk in the Control group. The infarct size was less in the morphine or ischemic preconditioning groups (MPC: 23 ± 8%, IPC: 20 ± 5%; each P < 0.05 vs Control). Infarct size reduction was abolished by paxilline (MPC + Pax: 37 ± 7%, P < 0.05 vs MPC and IPC + Pax: 36 ± 6%, P < 0.05 vs IPC), whereas paxilline alone had no effect (Pax: 46 ± 7%, not significantly different from Control).

Conclusion

Cardioprotection by morphine-induced preconditioning is mediated by activation of mK_Ca channels.     

Volatile anesthetics mimic cardiac preconditioning by priming the activation of mitochondrial K(ATP) channels via multiple signaling pathways

BACKGROUND: Volatile anesthetics induce pharmacological preconditioning in cardiac tissue. The purpose of this study was to test whether volatile anesthetics mediate this effect by activation of the mitochondrial adenosine triphosphate-sensitive potassium (mitoK(ATP)) or sarcolemmal K(ATP) (sarcK(ATP)) channel in rat ventricular myocytes and to evaluate the signaling pathways involved. METHODS: A cellular model of ischemia with subsequent hypoosmolar trypan blue staining served to determine the effects of 5-hydroxydecanoate, a selective mitoK(ATP) channel blocker, HMR-1098, a selective sarcK(ATP) channel blocker, diazoxide, a preconditioning mimicking agent, and various modulators of putative signaling pathways on cardioprotection elicited by sevoflurane and isoflurane. Microscopy was used to visualize and measure autofluorescence of flavoproteins, a direct index of mitoK(ATP) channel activity. RESULTS: Volatile anesthetics significantly enhanced diazoxide-mediated activation of mitoK(ATP) channels as assessed by autofluorescence of myocytes. Conversely, volatile anesthetics alone did not alter mitoK(ATP) channel activity, implying a priming effect of volatile anesthetics on mitoK(ATP) channels. Administration of the protein kinase C inhibitor chelerythrine completely blocked this effect. Also, pretreatment with volatile anesthetics potentiated diazoxide-mediated protection against ischemia, as indicated by a reduction in trypan blue-positive myocytes. Importantly, cardioprotection afforded by volatile anesthetics was unaffected by the sarcK(ATP) channel blocker HMR-1098 but sensitive to modulations of nitric oxide and adenosine-G(i) signaling pathways. CONCLUSIONS: Using autofluorescence in live cell imaging microscopy and a simulated model of ischemia, the authors present evidence that volatile anesthetics mediate their protection in cardiomyocytes by selectively priming mitoK(ATP) channels through multiple triggering protein kinase C-coupled signaling pathways. These observations provide important new insight into the mechanisms of anesthetic-induced preconditioning.     

HL-1 myocytes exhibit PKC and K(ATP) channel-dependent delta opioid preconditioning

BACKGROUND: Opioid preconditioning protects the myocardium against ischemia/reperfusion (IR) injury. By enhancing cardiomyocyte viability, opioids can enhance cardiac function and recovery from IR injury during acute cardiac care. The myocyte model HL-1 is an immortalized, mouse atrial cell line that expresses functional delta-opioid receptors. The HL-1 myocyte may be useful for IR injury research exploring opioid cardioprotection. MATERIALS AND METHODS: In study I, microplates of HL-1 were subjected to 10 min pre-treatment with either basal media, delta-opioid agonist DADLE(10uM), or DADLE(10uM) + delta-antagonist naltrindole (10uM). Study II treatment groups included PKC inhibitor chelerythrine (2uM), K(ATP) channel closer glybenclamide (100uM), or mitochondrial K(ATP) channel opener diazoxide (100uM) administered in various combinations followed by DADLE (10uM) or control. Microplates were subjected to normal oxygen/substrate conditions or ischemic (<1% 0(2)) and substrate deficient (10 uM 2-Deoxyglucose versus 10 mM glucose) conditions, then reperfused with normal oxygen and glucose-containing media. Microplate supernatants were subjected to lactate dehydrogenase (LDH) assay. RESULTS: Compared to untreated control, the LDH assay showed significant reduction in opioid-only pretreated groups at all time points. These effects were attenuated with delta-opioid antagonist co-administration. Co-administration of non-selective K(ATP) channel closer glybenclamide and DADLE abolished DADLE cytoprotection, while selective mitochondrial K(ATP) opener diazoxide mimicked DADLE cytoprotection Co-administration of chelerythrine and DADLE significantly reduced chelerythrine cytotoxicity. CONCLUSION: Delta-opioid preconditioning of HL-1 myocytes significantly decreased necrosis from in vitro simulated ischemia/reperfusion as measured by LDH release; this effect was reversed by delta-antagonist naltrindole. Cytoprotection was PKC and K(ATP) channel-dependent. HL-1 myocytes exhibit opioid-induced cytoprotection from IR injury, and present a novel model of pharmacologic preconditioning.     

Morphine enhances isoflurane-induced postconditioning against myocardial infarction: the role of phosphatidylinositol-3-kinase and opioid receptors in rabbits

Isoflurane reduces myocardial infarct size during early reperfusion by activating phosphatidylinositol-3-kinase (PI3K) signaling. We tested the hypothesis that this cardioprotection against reperfusion injury is enhanced by morphine and that a decrease in apoptosis plays a role in preservation of myocardial viability. Rabbits (n = 108) instrumented for hemodynamic measurement and subjected to a 30-min coronary occlusion followed by 3 h reperfusion received 0.9% saline, the selective PI3K inhibitor wortmannin (0.6 mg/kg), or the nonselective opioid antagonist naloxone (6 mg/kg) before coronary occlusion in the presence or absence of isoflurane (0.5 or 1.0 MAC), morphine (0.05 or 0.1 mg/kg), or their combination administered for 3 min before and 2 min after reperfusion. Infarct size was determined using triphenyltetrazolium staining and apoptosis assessed using cytochrome c translocation and Terminal Deoxynucleotidyl Transferase-Mediated dUTP Nick End Labeling (TUNEL) staining of left ventricular myocardium in situ. Isoflurane (1.0 but not 0.5 MAC) and morphine (0.1 but not 0.05 mg/kg) reduced (P < 0.05) infarct size (mean +/- sd 21% +/- 4%, 44% +/- 6%, 19% +/- 4%, and 41% +/- 6% of left ventricular area at risk, respectively) as compared with control (41% +/- 4%). The combination of 0.5 MAC isoflurane and 0.05 mg/kg morphine also decreased infarct size (18% +/- 9%). Wortmannin and naloxone alone did not affect infarct size but blocked the protection produced by isoflurane, morphine, and their combination. Isoflurane and morphine reduced cytochrome c translocation and TUNEL staining. The results indicate that morphine enhances isoflurane-induced postconditioning by activating PI3K and opioid receptors in vivo. A reduction in apoptotic cell death contributes to preservation of myocardial integrity during postconditioning by isoflurane. IMPLICATIONS: The results of this study indicate that morphine enhances isoflurane-induced postconditioning by activating phosphatidylinositol-3-kinase and opioid receptors in vivo. A reduction in apoptotic cell death contributes to preservation of myocardial integrity during postconditioning by isoflurane and morphine.     

The mitochondrial K(ATP) channel and cardioprotection

Adenosine triphosphate (ATP)-sensitive potassium (K(ATP)) channels allow coupling of membrane potential to cellular metabolic status. Two K(ATP) channel subtypes coexist in the myocardium, with one subtype located in the sarcolemma (sarcK(ATP)) membrane and the other in the inner membrane of the mitochondria (mitoK(ATP)). The K(ATP) channels can be pharmacologically modulated by a family of structurally diverse agents of varied potency and selectivity, collectively known as potassium channel openers and blockers. Sufficient evidence exists to indicate that the K(ATP) channels and, in particular, the mitoK(ATP) channels play an important role both as a trigger and an effector in surgical cardioprotection. In this review, the biochemistry and surgical specificity of the K(ATP) channels are examined.     

The role of nitric oxide, K(+)(ATP) channels, and cGMP in the preconditioning response of the rabbit

BACKGROUND: The role of nitric oxide (NO), K(+)(ATP) channels, and cyclic GMP (cGMP) in preconditioning is unknown. MATERIAL AND METHODS: Isolated rabbit hearts were pretreated with the NO precursor L-arginine (L-Arg), both alone and after infusion of the NO synthetase inhibitor N(G)-nitro-L-arginine methyl ester (L-NAME). Guanylate cyclase inhibitor methylene blue (MB) was infused prior to L-Arg in a separate group of hearts. To contrast the mechanisms of NO preconditioning and potassium channel opener (PCO) preconditioning, we infused the PCO pinacidil after L-NAME and the PCO blocker glibenclamide before L-Arg. Control hearts had no drug infused. The LAD coronary artery was occluded for 1 h and reperfused for 1 h in all hearts. Action potential duration (APD(50)), coronary flow (CF), and left ventricular developed pressure (DP) were measured, and infarct size (IS) was determined and expressed as a percentage of the area at risk. RESULTS: L-Arg prolonged APD(50) at 60 min of reperfusion (94 +/- 6 ms vs 69 +/- 2 ms (control) vs 70 +/- 2 ms (L-NAME) vs 74 +/- 3 ms (MB), P < 0.05). L-Arg reduced IS compared with control (24 +/- 2% vs 49 +/- 3%, P < 0.05); this was reversed by either L-NAME (53 +/- 4%, P < 0.05) or MB (43 +/- 3%, P < 0.05), but not by glibenclamide (20 +/- 4%), unlike the increase in CF during L-Arg infusion, which was blocked by glibenclamide. Pinacidil infusion decreased IS (26 +/- 2%), but this effect was blocked by L-NAME (53 +/- 7%, P < 0.05 vs pinacidil), although L-NAME did not blunt the increase in CF. There were no significant differences in DP among groups. CONCLUSION: L-Arginine preconditions the heart through NO generation, and this response is mediated through a cGMP-dependent mechanism, but is independent of the K(+)(ATP) channels. Coronary vasodilation is mediated through a mechanism different from that responsible for cardiomyocyte preconditioning.     

Ethanol enhances the functional recovery of stunned myocardium independent of K(ATP) channels in dogs

Chronic, intermittent exposure to small amounts of ethanol reduces myocardial infarct size in vivo. We tested the hypothesis that acute administration of ethanol enhances the functional recovery of stunned myocardium and that adenosine triphosphate-dependent potassium (K(ATP)) channels mediate this beneficial effect. Barbiturate-anesthetized dogs were instrumented for measurement of aortic and left ventricular pressure, +dP/dt(max), and subendocardial segment shortening (%SS) and were subjected to five 5-min periods of coronary artery occlusion, each separated by 5 min of reperfusion followed by a 3-h final reperfusion. In four groups (n = 7 each), dogs received 0.9% saline or ethanol (0.25, 0.5, or 1.0 g/kg over 30 min) in a random manner before occlusions and reperfusions. In other groups (n = 7 each), dogs received the K(ATP) channel antagonist glyburide (0.3 mg/kg, IV) 30 min before saline or ethanol (0.25 g/kg) was administered. Dogs receiving saline or glyburide alone demonstrated poor recovery of contractile function during reperfusion (%SS = 0.9% +/- 2.0% and 1.6% +/- 1.2% at 3 h, respectively). Recovery of %SS was enhanced in dogs receiving the 0.25- and 0.5-g/kg doses of ethanol (10.0% +/- 1.8% and 8.6% +/- 2.2% at 3 h, respectively) independent of alterations in hemodynamics or coronary collateral blood flow (radioactive microspheres). Glyburide did not affect improvement of recovery of stunned myocardium produced by ethanol (11.8% +/- 2.2% at 3 h). The results indicate that ethanol enhances the functional recovery of stunned myocardium independent of K(ATP) channels in vivo.     

Sevoflurane preconditioning before moderate hypothermic ischemia protects against cytosolic [Ca(2+)] loading and myocardial damage in part via mitochondrial K(ATP) channels

BACKGROUND: Brief sevoflurane exposure and washout (sevoflurane preconditioning [SPC]) before 30-min global ischemia at 37 degrees C is known to improve cardiac function, decrease cytosolic [Ca(2+)] loading, and reduce infarct size on reperfusion. It is not known if anesthetic preconditioning (APC) applies as well to hypothermic ischemia and reperfusion and if K(ATP) channels are involved. The authors examined in guinea pig isolated hearts the effect of sevoflurane exposure before 4-h global ischemia at 17 degrees C on cardiac function, cytosolic [Ca(2+)] loading, and infarct size. In addition they tested the potential role of the mitochondrial K(ATP) channel in eliciting the cardioprotection by SPC. METHODS: Hearts were randomly assigned to (1) a nontreated hypothermic ischemia group (CON), (2) a group given 3.5 vol% sevoflurane for 15 min with a 15-min washout before hypothermic ischemia (SPC), and (3) an SPC group in which anesthetic exposure was bracketed with 200 microm 5-hydroxydecanoate (5-HD) from 5 min before until 5 min after sevoflurane (SPC + 5-HD). Cytosolic [Ca(2+)] was measured in the left ventricular (LV) free wall with the intracellularly loaded fluorescence probe indo-1. RESULTS: Initial reperfusion in CON hearts markedly increased systolic and diastolic [Ca(2+)] and reduced contractility (dLVP/dt(max)), relaxation (diastolic LVP, dLVP/dt(min)), myocardial oxygen consumption (MvO(2)), and cardiac efficiency. In SPC hearts, cytosolic [Ca(2+)] overloading (especially diastolic [Ca(2+)]) was decreased with increased myocardial [Ca(2+)] influx (d[Ca(2+)]/dt(max)) and efflux (d[Ca(2+)]/dt(min)), improved contractility, relaxation, coronary flow, MvO(2), cardiac efficiency, and decreased infarct size. In SPC + 5HD hearts, the reduction in infarct size was antagonized by 5-HD, but functional return was less affected by 5-HD. CONCLUSIONS: Anesthetic preconditioning occurs after long-term hypothermic ischemia, and the infarct size reduction is the result, in part, of mitochondrial K(ATP) channel opening.     

Contractile recovery of heart muscle after hypothermic hypoxia is improved by nicorandil via mitochondrial K(ATP) channels.

BACKGROUND: The ATP-sensitive potassium channel (K(ATP)) opener nicorandil used instead of potassium in hypothermic cardioplegia significantly improves preservation of cardiac function and energetics in the in situ heart preparation. The present study, therefore, examines the effect of nicorandil at different temperatures and the role of sarcolemmal and mitochondrial K(ATP) channels under ex vivo conditions using contractile force (CF) and action potential duration (APD) as end points. METHODS: Guinea-pig papillary muscles at 37, 27, or 22 degrees C (1Hz) were exposed to nicorandil 0.2-1.1 mM. The contributions of K(ATP) channel subtypes in cardioprotection were examined using mitochondrial (mito) (0.1 mM) or non-selective (1.0 mM) concentrations of nicorandil, mito K(ATP) blocker 5-hydroxyl decanoate (5HD, 300 microM) or sarcolemmal (sarc) K(ATP) blocker HMR1098 (30 microM) before and during 140 min of hypothermic (22 degrees C) glucose-free hypoxia. RESULTS: Nicorandil >0.5 mM shortened the APD, and this was abolished by hypothermia and HMR1098 but not by 5HD. Nicorandil in both tested concentrations preserved contractile force after hypoxia-reoxygenation significantly better than control (73.7+/-4.4% and 75.8+/-3.9% vs 40.6+/-2.6%, n=6 in each group). Protection was blocked by 5HD but not by HMR1098. 5HD and HMR1098 alone did not change recovery of contractile force compared to control. CONCLUSION: Shortening of APD and activation of sarc K(ATP) by nicorandil were not related to myocardial protection. Thus, the mito K(ATP) seems to play a significant role in cardioprotection compared to the sarc K(ATP) also when substrate depletion and hypoxia are combined with hypothermia.     

外周和中枢阿片受体诱导心脏预处理保护作用及信号转导机制

The majority of investigations about the cardioprotection induced by opioid preconditioning was focused on the role played by myocardial opioid receptors and the of signal mechanism. However, it has been found that directly activation of the opioid receptors in the central nervous system by intracerebroventricular/intrathecal morphine preconditioning also could mimic cardioprotective effects induced by ischemia preconditioning against ischemia-reperfusion injury, one had found also, the k-,δ- andμ-ORs of central nervous system were implicated in modulating the protective effect. This effect was probably induced by neurohumoral and analgesic substances.     

外周和中枢阿片受体诱导心脏预处理保护作用及信号转导机制

The majority of investigations about the cardioprotection induced by opioid preconditioning was focused on the role played by myocardial opioid receptors and the of signal mechanism. However, it has been found that directly activation of the opioid receptors in the central nervous system by intracerebroventricular/intrathecal morphine preconditioning also could mimic cardioprotective effects induced by ischemia preconditioning against ischemia-reperfusion injury, one had found also, the k-,δ- andμ-ORs of central nervous system were implicated in modulating the protective effect. This effect was probably induced by neurohumoral and analgesic substances.     

外周和中枢阿片受体诱导心脏预处理保护作用及信号转导机制

前期的研究关于阿片类药物预处理的心肌保护效应,主要集中在心脏上的阿片受体在这种保护效应中的作用及信号机制.然而最新的研究已经发现通过中枢(侧脑室内,鞘内)注射吗啡预处理可以直接激活中枢阿片受体,同样可以模拟经典的缺血预处理(ischemia precondition,IPC)心肌保护效应,并且发现中枢神经系统3种阿片受体均参与介导了这种保护作用.这种保护作用的机制可能与痛觉的干预和神经递质的释放等效应有关.     

Protein tyrosine kinase-dependent modulation of isoflurane effects on cardiac sarcolemmal K(ATP) channel

BACKGROUND: Cardiac adenosine triphosphate-sensitive potassium (K(ATP)) channels and protein tyrosine kinases (PTKs) are mediators of ischemic preconditioning, but the interaction of both and a role in myocardial protection afforded by volatile anesthetics have not been defined. METHODS: Whole cell and single channel patch clamp techniques were used to investigate the effects of isoflurane and the PTK inhibitor genistein on the cardiac sarcolemmal K(ATP) channel in acutely dissociated guinea pig ventricular myocytes. RESULTS: At 0.5 mm internal ATP, genistein (50 microm) elicited whole cell K(ATP) current (22.5 +/- 7.9 pA/pF). Genistein effects were concentration-dependent, with an EC50 of 32.3 +/- 1.4 microm. Another PTK inhibitor, tyrphostin B42, had a similar effect. The inactive analog of genistein, daidzein (50 microm), did not elicit K(ATP) current. Isoflurane (0.5 mm) increased genistein (35 microm)-activated whole cell K(ATP) current from 14.5 +/- 3.1 to 32.5 +/- 6.6 pA/pF. Stimulation of receptor PTKs with epidermal growth factor, nerve growth factor, or insulin attenuated genistein and isoflurane effects, and the protein tyrosine phosphatase inhibitor orthovanadate (1 mm) prevented their actions on K(ATP) current. In excised inside-out membrane patches, and at fixed 0.2 mm internal ATP, genistein (50 microm) increased channel open probability from 0.053 +/- 0.016 to 0.183 +/- 0.039, but isoflurane failed to further increase open probability (0.162 +/- 0.051) of genistein-activated channels. However, applied in the presence of genistein and protein tyrosine phosphatase 1B (1 microg/ml), isoflurane significantly increased open probability to 0.473 +/- 0.114. CONCLUSIONS: These results suggest that the PTK-protein tyrosine phosphatase signaling pathway may be one of the regulators of cardiac sarcolemmal K(ATP) channel and may play a role in modulating its responsiveness to isoflurane. Relative importance of this modulation for cardioprotection by volatile anesthetics remains to be established.     

Inhibition of mitochondrial permeability transition enhances isoflurane-induced cardioprotection during early reperfusion: the role of mitochondrial KATP channels

Inhibition of the mitochondrial permeability transition pore (mPTP) mediates the protective effects of brief, repetitive ischemic episodes during early reperfusion after prolonged coronary artery occlusion. Brief exposure to isoflurane immediately before and during early reperfusion also produces cardioprotection, but whether mPTP is involved in this beneficial effect is unknown. We tested the hypothesis that mPTP mediates isoflurane-induced postconditioning and also examined the role of mitochondrial KATP (mKATP) channels in this process. Rabbits (n = 102) subjected to a 30-min coronary occlusion followed by 3 h reperfusion received 0.9% saline (control), isoflurane (0.5 or 1.0 MAC) administered for 3 min before and 2 min after reperfusion, or the mPTP inhibitor cyclosporin A (CsA, 5 or 10 mg/kg) in the presence or absence of the mPTP opener atractyloside (5 mg/kg) or the selective mK(ATP) channel antagonist 5-hydroxydecanoate (5-HD; 10 mg/kg). Other rabbits received 0.5 MAC isoflurane plus 5 mg/kg CsA in the presence and absence of atractyloside or 5-HD. Isoflurane (1.0 but not 0.5 MAC) and CsA (10 but not 5 mg/kg) reduced (P < 0.05) infarct size (21% +/- 4%, 44% +/- 6%, 24% +/- 3%, and 43% +/- 6%, respectively, mean +/- sd of left ventricular area at risk; triphenyltetrazolium staining) as compared with control (42% +/- 7%). Isoflurane (0.5 MAC) plus CsA (5 mg/kg) was also protective (27% +/- 4%). Neither atractyloside nor 5-HD alone affected infarct size, but these drugs abolished protection by 1.0 MAC isoflurane, 10 mg/kg CsA, and 0.5 MAC isoflurane plus 5 mg/kg CsA. The results indicate that mPTP inhibition enhances, whereas opening abolishes, isoflurane-induced postconditioning. This isoflurane-induced inhibition of mitochondrial permeability transition is dependent on activation of mitochondrial KATP channels in vivo.     

Donor heart preservation with pinacidil: the role of the mitochondrial K ATP channel

Background

Pinacidil solutions have been shown to have significant cardioprotective effects. Pinacidil activates both sarcolemmal and mitochondrial potassium-adenosine triphosphate (K_ATP) channels. This study was undertaken to compare pinacidil solution with University of Wisconsin (UW) solution and to determine if the protective effect of pinacidil involved mitochondrial or sarcolemmal K_ATP channels.

Methods

Thirty-two rabbit hearts received one of four preservation solutions in a Langendorff apparatus: (1) UW; (2) a solution containing 0.5 mmol/L pinacidil; (3) pinacidil with Hoechst-Marion-Roussel 1098 (HMR-1098), a sarcolemmal channel blocker; and (4) pinacidil with 5-hydroxydecanote, a mitochondrial channel blocker. Left ventricular pressure-volume curves were generated by an intraventricular balloon. All hearts were placed in cold storage for 8 hours, followed by 60 minutes of reperfusion.

Results

Postischemic developed pressure was better preserved by pinacidil than by UW. This cardioprotective effect was eliminated by 5-hydroxydecanote and diminished by HMR-1098. Diastolic compliance was better preserved by pinacidil when compared with UW. This protection was abolished by the addition of 5-hydroxydecanote and moderately decreased by HMR-1098.

Conclusions

Our results support the superiority of pinacidil over UW after 8 hours of storage. The cardioprotective role of pinacidil is mediated primarily by the mitochondrial K_ATP channel.