Temperature Preconditioning Research Articles

A combined technique of temperature preconditioning and modified atmosphere packaging to prolong the storage life of papaya

Papaya is a popular tropical fruit for human consumption over the world. However, it has a relatively short shelf life due to rapid ripening and anthracnose infection after harvest. Generally, papaya is stored at the optimum temperature of 12°C and can last only two weeks. After this period, the fruit will begin to ripen and spoil. Theoretically, fruit stored at lower temperatures will have a longer shelf life. However, papaya is prone to chilling injuries characterised by pitting and inability to ripen if stored at sub-optimum temperature, which may also cause secondary postharvest disease attacks if held for a longer period. The study aimed to evaluate the effectiveness of a combination of temperature preconditioning treatment and modified atmospheric packaging (MAP) in prolonging the storage life of papaya under sub-optimum temperature. In terms of visual appearance, no chilling injury symptoms were observed in samples stored at a suboptimum temperature of 7°C throughout the storage period. No significant differences were recorded in the parameters of total soluble solids (TSS), total titratable acidity (TTA) and TSS: TTA ratio. Relatively lower ascorbic acid content and higher firmness value were recorded in fruits subjected to the combined technique of temperature conditioning and MAP, which could be associated with delayed ripening. A combination of temperature preconditioning and MAP techniques maintains the papaya quality under storage at sub-optimum temperatures as low as 7°C without chilling injury problems, with a longer shelf life (4 weeks) than only 2 weeks for conventional handling techniques. The fruits can be ripened by being exposed to ethylene when they are ready to be marketed. The technology is helpful for the industry, farmers, wholesalers, and exporters, particularly for the delivery of more extended distribution and periods.

Flexibility Quantification and the Potential for Its Usage in the Case of Electric Bus Depots with Unidirectional Charging

One of the crucial steps for a successful integration of electric bus fleets into the existing electric power systems is the active and intelligent usage of their flexibility. This is important not only for reducing the eventual negative effects on the power grid but also for reducing energy and infrastructure costs. The first step in the optimal usage of flexibility is its quantification, which allows the maximum provision of flexibility without any negative effects for the fleet operation. This paper explores the available flexibility of large-scale electric bus fleets with a concept of centralized and unidirectional depot charging. An assessment of available positive and negative flexibility was conducted based on the data from two real bus depots in the city of Hamburg, Germany. The analysis shows the biggest flexibility potential was in the period from 16:00 h to 24:00 h, and the smallest one was in the periods from 08:00 h to 16:00 h, as well as from 02:00 h to 08:00 h. The paper also gives an overview of the possible markets for flexibility commercialization in Germany, which can provide an additional economic benefit for the fleet operators. A further analysis of the impact of parameters such as the timeline (working day or weekend), charging concept, ambient temperature, and electrical preconditioning provides an additional understanding of available flexibility.

Effect of Temperature Pre-conditioning on Fruit Quality of Early-season ‘Hanareum’ Pears (Pyrus pyrifolia Nakai) during Simulated Marketing

본 연구에서는 수확 후 예건처리를 통해 ‘한아름’ 배 과실의 상온유통 중 품질 유지를 위한 수확관리 기술을 정립하기 위해 실 시하였다. 과실은 만개 후 103일과 110일에 각각 수확하여 세 그룹의 처리 온도(21, 25, 29°C)에서 4일간 예건처리를 실시하였 다. 과실의 감모율은 수확시기에 관계없이 예건온도가 낮을수록 낮은 경향을 나타내었다. 과실의 경도는 상온 유통기간이 증 가함에 따라 모든 처리에서 경도가 감소하는 경향을 보였고 두 수확시기 모두 21°C 처리구가 경도유지에 가장 효과적인 것으 로 나타났다. 또한 21°C에서 예건한 경우, 상온유통 중 외관 품질이 높게 유지되었고 분질장해 등 생리장해의 발생은 낮게 조 사되었다. 상온유통 중 에틸렌 발생량은 조기수확과 및 적숙과 모두 비슷한 수준을 보였고 두 수확시기 모두 예건온도가 21°C 인 경우가 25 및 29°C에 비해 에틸렌 발생량이 적은 것으로 나타났다. 과실의 호흡량은 예건처리 기간 중에는 온도가 높을수록 호흡률이 높아 29°C 처리는 21°C 처리에 비해 호흡률이 2배 이상 높았고 조기수확과에 비해 적숙과가 호흡률이 높은 것으로 나타났는데 상온 유통기간 중에는 큰 차이를 보이지 않았다. 이상의 결과를 종합하면 한여름에 수확되는 조생종 ‘한아름’ 배에 있어 수확 후 21°C 예건처리는 상온유통 중 과실의 품질 유지를 위한 바람직한 수확 후 처리방법의 하나로 추천할 수 있을 것 으로 판단되었다.

Influence of abiotic stress preconditioning on antioxidant enzymes in shoot tips of Lomandra sonderi (Asparagaceae) prior to cryostorage

Lomandra sonderi (F.Muell.) Ewart (Asparagaceae) is endemic to the south-west Western Australian jarrah (Eucalyptus marginata Donn ex Sm.) forest region, and is a difficult to propagate species important to post-mining restoration. Micropropagation is the only way to currently produce plants of this species for restoration. This study describes investigations into optimising cryopreservation for efficient long-term germplasm storage. In order to investigate the effect of preconditioning on post-cryogenic survival of shoot tips, in vitro grown plants were exposed to a range of light-, temperature- and osmotic-induced preconditioning treatments under culture room conditions for 3 weeks. Room temperature (24°C) preconditioning resulted in the greatest post-cryogenic survival, followed by low light (17 µmol m–2 s–1) preconditioning. Alternating temperature (25/5°C), high temperature (35°C), high sucrose (180 mM) and high light (93 µmol m–2 s–1) preconditioning treatments all led to significantly and progressively lower post-cryogenic shoot tip survival than room temperature preconditioning. Antioxidant activity of superoxide dismutase in preconditioned shoot tips showed a positive correlation to post-cryogenic survival overall, whereas the activities of glutathione reductase, glutathione peroxidase and catalase showed little correlation. Analysis throughout the cryopreservation protocol showed that the activity of glutathione reductase decreased significantly after cryopreservation, whilst the activity of glutathione peroxidase and catalase did not change.

EPAC IS A KEY MEDIATOR OF cAMP-INDUCED CARDIOPROTECTIVE SIGNALLING

It has been shown that cyclic AMP (cAMP)-induced protein kinase A (PKA) activation is very important in a variety of cardioprotective protocols including ischaemic and temperature preconditioning. However, it has been recently found that cAMP can also directly activate Epac. Our data show that a cell permeable cAMP analogue 8-Br-cAMP-AM (8-BR), which activates both PKA and Epac, can protect heart against ischaemia/reperfusion injury. The purpose of our study was to determine whether Epac activation is involved in the cAMP-induced cardioprotection. Experiments were carried out on Langendorff-perfused rat heart and on rat heart myoblasts H9C2. Along with 8-Br, the following cAMP analogues and inhibitors were used: an activator of PKA only, 6-Bnz-cAMP-AM (6-Bnz); activators of Epac only, 8-Br-2′-O-Me-cAMP-AM (O-Me) and 8-CPT-2′-O-Me-cAMP-AM (CPT); a PKA inhibitor H-89 and an Epac inhibitor ESI-09. Exposure of the H9C2 cells to these compounds revealed that 10 µM O-Me and 5 µM 8-Br activate Epac to a similar extent whilst ESI-09 completely blocks this effect of 8-Br. Perfusion of hearts with 10 µM 6-Bnz appeared to activate PKA to the same extent as 5 µM 8-Br. Further experiments demonstrated that neither 6-Bnz nor O-Me can produce cardioprotective effect similar to 8-Br. However, both H-89 and ESI-09 completely abolish 8-Br-induced cardioprotection whilst a mixture of 6-Bnz and CPT induced a strong protective effect. These data imply that activation of Epac alone is unable to protect the heart against ischaemia/reperfusion injury but it represents an essential link in cAMP-induced cardioprotection when activated together with PKA.

MANAGING CHILLING INJURY IN VEGETABLES

Common vegetables that are susceptible to chilling injury include asparagus, beans, cucumbers, eggplants, ginger, jicama, okra, peppers, potatoes, pumpkins, sweet potatoes, tamarillos, tomatoes, and zucchini squashes. Most of the susceptible crops are either fruit vegetables or root vegetables. Chilling injury symptoms vary depending on the commodity, but generally manifest as pitting, discoloration, internal breakdown, and decay. Images from nuclear magnetic resonance revealed that signals on the peripheral of cells in chilled zucchini tissues were much more intense than those in non-chilled tissues, indicating that cell membranes were damaged by chilling which leads to the increased permeability and solute leakage. Several postharvest techniques have been demonstrated to be effective in managing chilling injury in vegetables, including temperature preconditioning, intermittent warming, high oxygen atmosphere, heat treatment, modified atmosphere packaging, and treatment with growth regulators or natural products as well as harvesting at proper maturity. Treatment with certain naturally occurring compounds such as methyl jasmonate (MJ) or methyl salicylate (MS) increased activities of alternative oxidase (AOX) in the respiratory pathway of sweet pepper and enhanced amounts of high and low molecular weight heat shock proteins (HSP) and pathogenesis-related proteins (PRP) in tomatoes. Temperature preconditioning treatment elevated antioxidant content and antioxidant enzyme activities, and augmented s-adenosylmethionine (SAM) decarboxylase activities and increased the levels of spermidine and spermine in zucchini squash. These defense responses induced by these treatments might be part of the mechanisms that protected and prevented tissues from chilling injury. Promising techniques and new methods such as genetic engineering and transgenic skill need to be exploited for better management of chilling injury.

Odour assessment: determining the optimum temperature and time for Tedlar sampling bag pre-conditioning

Odours present in new Tedlar bags can impact the assessment of emissions from sewer collection systems and wastewater treatment plants. Conditioning protocols are needed to minimise the impact of background materials emissions on the sampling and assessment of odourous emissions. Olfactometry analysis has shown that background odour concentrations for new Tedlar bags can be as high as 130 OU(E)/m(3). Experimental studies were undertaken to investigate the impact of different conditioning temperatures in order to determine the optimum temperature for cleaning new Tedlar bags to a level when no detectable odours were present in the sampling bags via dilution olfactometry. For the purpose of this study, new Tedlar bags were cleaned in a temperature-controlled oven that had a constant filtered air flow-rate. From the analysis of odour and volatile organic compounds (VOCs) concentrations found in new Tedlar bags during the cleaning process, it was observed that odour and VOCs concentrations decreased with time. It was also found that the temperature setting plays a significant role in the cleaning of the Tedlar bags as large concentrations of phenols and acetamide, N,N-dimethyl were found in new Tedlar bags and their concentrations decreased following the temperature pre-conditioning.

Mitochondrial ROS production and subsequent ERK phosphorylation are necessary for temperature preconditioning of isolated ventricular myocytes

Hypothermia and hypothermic preconditioning are known to be profoundly cardioprotective, but the molecular mechanisms of this protection have not been fully explained. In this study, temperature preconditioning (16 °C) was found to be cardioprotective in isolated adult rat ventricular myocytes, enhancing contractile recovery and preventing calcium dysregulation after oxidative stress. Hypothermic preconditioning preserved mitochondrial function by delaying the pathological opening of the mitochondrial permeability transition pore (mPTP), whereas transient mPTP flickering remained unaltered. For the first time, reactive oxygen species (ROS) from the mitochondria are shown to be released exclusively during the hypothermic episodes of the temperature-preconditioning protocol. Using a mitochondrially targeted ROS biosensor, ROS release was shown during the brief bursts to 16 °C of temperature preconditioning. The ROS scavenger N-(2-mercaptopropionyl) glycine attenuated ROS accumulation during temperature preconditioning, abolishing the protective delay in mPTP opening. Temperature preconditioning induces ROS-dependant phosphorylation of the prosurvival kinase extracellular signal-regulated kinase (ERK)1/2. ERK1/2 activation was shown to be downstream of ROS release, as the presence of a ROS scavenger during temperature preconditioning completely blocked ERK1/2 activation. The cardioprotective effects of temperature preconditioning on mPTP opening were completely lost by inhibiting ERK1/2 activation. Thus, mitochondrial ROS release and ERK1/2 activation are both necessary to signal the cardioprotective effects of temperature preconditioning in cardiac myocytes.

12 ERK activation is necessary for temperature preconditioning in isolated adult rat ventricular myocytes

In the present study we investigated the molecular effects of temperature preconditioning (TP) in freshly isolated adult rat cardiac myocytes. TP consisted of incubating myocytes at 16°C for 2 min,...

Temperature preconditioning is optimal at 26°C and confers additional protection to hypothermic cardioplegic ischemic arrest

We have recently shown that brief episodes of hypothermic perfusion interspersed with periods of normothermic perfusion, referred to as temperature preconditioning (TP), are cardioprotective and can be mimicked by consecutive isoproterenol/adenosine treatment. Here we investigate the optimal temperature for TP and whether TP further enhances protection provided by hypothermic ischemia with or without polarized cardioplegic arrest. Three experimental groups of Langendorff-perfused rat hearts were used. In the first group, hearts were subjected to three episodes of hypothermic perfusion at 7, 17, 26 and 32°C during the TP protocol, followed by 30 min normothermic index ischemia and 60 min reperfusion (37°C). Protein kinase A (PKA) activity and cyclic AMP (cAMP) concentrations were measured prior to index ischemia. In the second group, TP (26°C) hearts were subjected to two hours hypothermic index ischemia at 26°C and two hours normothermic reperfusion. In the third group, TP (26°C) hearts or hearts treated with isoproterenol/adenosine (pharmacological simulation of TP) were subjected to four hours hypothermic index ischemia with procaine-induced polarized cardioplegia at 26°C followed by two hours normothermic reperfusion. Hemodynamic function recovery, lactate dehydrogenase release and infarct size were used to assess cardioprotection. TP at 26°C resulted in highest cardioprotection, increased cAMP concentration and PKA activity, while TP at 7°C exacerbated ischemia/reperfusion damage, and had no effect on cAMP concentration or PKA activity. TP at 26°C also protected hearts during hypothermic ischemia with or without polarized cardioplegia. Isoproterenol/adenosine treatment conferred additional protection similar to TP. In conclusion, the study shows that TP-induced cardioprotection is temperature dependent and is optimal at 26°C; TP confers additional protection to hypothermia and polarized cardioplegia; and that the pharmacological treatment based on the mechanism of TP (consecutive isoproterenol/adenosine treatment) is a potential cardioprotective strategy that can be used during heart surgery and transplantation.

The Cardioprotective Effects of Temperature Preconditioning on Isolated Ventricular Myocytes

In ex vivo whole heart studies temperature preconditioning (TP) has been found to confer cardioprotection (Khaliulin et al. 2007). Here we have investigated the molecular effects of TP in freshly isolated adult rat cardiac myocytes. To assess the affect of TP we measured; contractile function, Ca2+ homeostasis and mitochondrial permeability transition pore (MPTP) opening. TP consisted of three cycles of 2 minutes at 12°C and 3 minutes at 37°C. Contraction of myocytes was synchronized by electrical field stimulation (1Hz) and recovery of contractile function was measured following simulated ischaemia/reperfusion injury. This consisted of 7 minutes perfusion with substrate-free Tyrode solution containing cyanide (2mM) and iodoacetic acid (1mM) followed by 10 minutes reperfusion with Tyrode solution. A significant increase in contractile function after TP (52%±6 n=225, 3) was observed compared to control (29%±5 n=229, 3) (p<0.05). To identify whether this protection was linked to changes in Ca2+ handling, we analysed Ca2+ levels at 10 minutes reperfusion. We found that TP myocytes had significantly lower Ca2+ levels (131nM n=67, 3) compared to controls (301nM n=69, 3) (p<0.005). MPTP opening is thought to be a critical event in the determination of myocyte fate following ischaemia/reperfusion injury. Therefore we investigated the effects of TP on the time to induce MPTP opening in response to photodamage using TMRM, a mitochondrial selective dye. We found that TP myocytes significantly delayed time to MPTP opening (15.2±0.6 n=126, 3) compared to controls (11.9±0.4 n=168, 3) (p<0.0001). TP confers protection to isolated myocytes by significantly increasing recovery of contractile function and preventing calcium overload in response to simulated ischaemia/reperfusion. TP also significantly delays MPTP opening after simulated ischaemia/reperfusion injury. Data presented as mean±SEM, n=myocytes, animals. Khaliulin et al., J physio 581.3 (2007) 1147-1161. Funded by The British Heart Foundation.

Consecutive pharmacological activation of PKA and PKC mimics the potent cardioprotection of temperature preconditioning

AimsTemperature preconditioning (TP) provides very powerful protection against ischaemia/reperfusion. Understanding the signalling pathways involved may enable the development of effective pharmacological cardioprotection. We investigated the interrelationship between activation of protein kinase A (PKA) and protein kinase C (PKC) in the signalling mechanisms of TP and developed a potent pharmacological intervention based on this mechanism.Methods and resultsIsolated rat hearts were subjected to TP, 30 min global ischaemia, and 60 min reperfusion. Other control and TP hearts were perfused with either sotalol (β-adrenergic blocker) or H-89 (PKA inhibitor). Some hearts were pre-treated with either isoproterenol (β-adrenergic agonist) or adenosine (PKC activator) that were given alone, simultaneously, or sequentially. Pre-treatment with isoproterenol, adenosine, and the consecutive isoproterenol/adenosine treatment was also combined with the PKC inhibitor chelerythrine. Cardioprotection was evaluated by haemodynamic function recovery, lactate dehydrogenase release, measurement of mitochondrial permeability transition pore opening, and protein carbonylation during reperfusion. Cyclic AMP and PKA activity were increased in TP hearts. H-89 and sotalol blocked the cardioprotective effect of TP and TP-induced PKC activation. Isoproterenol, adenosine, and the consecutive treatment increased PKC activity during pre-ischaemia. Isoproterenol significantly reduced myocardial glycogen content. Isoproterenol and adenosine, alone or simultaneously, protected hearts but the consecutive treatment gave the highest protection. Cardioprotective effects of adenosine were completely blocked by chelerythrine but those of the consecutive treatment only attenuated.ConclusionThe signal transduction pathway of TP involves PKA activation that precedes PKC activation. Pharmacologically induced consecutive PKA/PKC activation mimics TP and induces extremely potent cardioprotection.

ALLEVIATION OF CHILLING INJURY IN TROPICAL AND SUBTROPICAL FRUITS

Chilling injury in tropical and subtropical fruits can be alleviated by low temperature preconditioning, intermittent warming, heat treatment, controlled atmosphere storage, treatments with calcium or other chemicals, waxing, film packaging, genetic modification, or applications with ethylene, abscisic acid, polyamines, methyl jasmonate, methyl salicylate, or other natural compounds. The effectiveness of each treatment varies with the commodity, the maturity of the fruit, and the dosage of the treatment. Low temperature conditioning and intermittent warming maintain high levels of phospholipids, increase the degree of unsaturation of fatty acids, increase the levels of spermidine and spermine, and stimulate the activities of free radical scavenging enzymes. Heat treatment induces heat shock proteins (HSP), suppresses oxidative activity, and maintains membrane stability. Methyl jasmonate and methyl salicylate stimulates the synthesis of some stress proteins, such as HSP, pathogenesis-related (PR)-proteins, and alternative oxidase (AOX) and can activate lipoxygenase gene expression and induce synthesis of abscisic acid and polyamines. Polyamines may act as free radical scavengers and membrane stabilizers. All of these processes can enhance chilling tolerance of tissues and alleviate chilling injury of tropical and subtropical fruits.

A SIMPLE CHESTNUT PEELING PROCESS AND PROPERTIES OF THE PEELED KERNELS

We developed a simple, fan-driven process to peel chestnuts that utilizes impact to remove shells and pellicle. A working prototype has peeled over 10 tons of Chinese chestnuts at a maximum peeling rate of 150 kg/h output. Capital costs and operating costs of the process are a fraction of the cost of steam or flame peeling technologies. The device peels partially dried, fresh chestnuts or completely dried chestnuts, removing both the shell and pellicle. The peeled chestnut kernels emerge in a fresh, uncooked condition. Fresh peeled kernels are perishable, but have a minimum 3-week shelf life under refrigeration. Alternatively, dried kernels and chestnut flour are shelf-stable products that can be derived from this process. Optimum peeling performance depends on proper temperature and moisture preconditioning. Color, texture, flavor, and shelf-life of peeled kernels depend on internal moisture content and storage temperature and humidity. Protocols for best peeling performance and subsequent marketing are based on 15 years' experience with this process. Kernel moisture content, sugar content, and microbiological risks are all interrelated factors that need to be controlled for successful commercial use of this process.

저속 유동 계산의 수렴성에 미치는 특성 조건수의 영향 I : 오일러 방정식

예조건화 오일러 방정식의 수렴 특성에 미치는 특성 조건수의 영향을 조사하였다. 그리고 Choi와 Merkle 예조건화를 적용한 경우와 온도 예조건화를 적용한 경우의 수렴 특성을 분석하였다. 공간차분을 위해 예조건화 Roe의 FDS 기법을 적용하였고, 시간적분을 위해 예조건화 LU-SGS 기법을 적용하였다. 지배방정식의 수렴 특성은 특성 조건수에 크게 영향을 받는 것으로 나타났으며, 최적의 특성 조건수가 존재하는 것으로 나타났다. 그리고 최적의 특성 조건수는 Choi 와 Merkle 예조건화를 적용한 경우와 온도 예조건화를 적용한 경우가 서로 다른 것으로 나타났다. The effects of characteristic condition number on the convergence of preconditioned Euler equations were investigated. The two-dimensional preconditioned Euler equations adopting Choi and Merkle's preconditioning and the temperature preconditioning are considered. Preconditioned Roe's FDS scheme was adopted for spatial discretization and preconditioned LU-SGS scheme was used for time integration. It is shown that the convergence characteristics of the Euler equations are strongly affected by the characteristic condition number, and there is an optimal characteristic condition number for a problem. The optimal characteristic condition numbers for the Choi and Merkle's preconditioning and temperature preconditioning are different.

저속 유동 계산의 수렴성에 미치는 특성 조건수의 영향 II : 나비어스톡스 방정식

예조건화 나비어스톡스 방정식의 수렴 특성에 미치는 특성 조건수의 영향을 조사하였다. Choi와 Merkle 예조건화를 적용한 경우와 온도 예조건화를 적용한 경우의 수렴 특성을 분석하였다. 공간차분을 위해 예조건화 Roe의 FDS 기법을 적용하였고, 시간적분을 위해 LU-SGS 기법을 적용하였다. 나비어스톡스 방정식의 수렴 특성은 특성 조건수에 크게 영향을 받으며, 최적의 특성 조건수가 존재하는 것을 보였다. 그리고 점성 유동의 최적 특성 조건수는 비점성 유동에 비해 큰 것으로 나타났다. The effects of characteristic condition number on the convergence of preconditioned Navier-Stokes equations were investigated. The two-dimensional preconditioned Navier-Stokes adopting Choi and Merkle's preconditioning and the temperature preconditioning are considered. Preconditioned Roe's FDS scheme was adopted for spatial discretization and preconditioned LU-SGS scheme was used for time integration. It is shown that the convergence characteristics of the Navier-Stokes equations are strongly affected by the characteristic condition number. Also it is shown that the optimal characteristic condition numbers for viscous flows are larger than that in inviscid flows.

저속 유동 계산의 수렴성 개선을 위한 온도예조건화 II: 나비어스톡스 방정식

온도예조건화 방법을 Navier-Stokes 방정식에 적용하여 보았다. 그리고 Navier-Stokes 방정식에 적절한 기준마하수를 결정하기 위해 확산마하수 개념을 도입하였다. 다양한 레이놀즈수에 대한 실린더 주위의 2차원 유동을 계산하였다. 온도예조건화를 Navier-Stokes 방정식에 적용한 결과, 수렴특성이 주목할 만큼 개선되는 것을 보였다. 그리고 확산마하수로 수정한 기준마하수는 국부적으로 마하수가 낮은 영역의 수렴성 문제를 상당히 완화시키는 것을 확인하였다. The temperature preconditioning is applied to the Navier-Stokes equations. Also, a new concept of diffusion Mach numbers is introduced to modify the reference Mach number for the Navier-Stokes equations. Flows over a circular cylinder were calculated at different Reynolds numbers. It is shown that the temperature preconditioning improves the convergence characteristics of Navier-Stokes equations. Also, it is shown that the modified reference Mach number alleviates the convergence problems at locally low speed regions.

Temperature preconditioning: a cold‐hearted answer to ischaemic–reperfusion injury?

Restoration of blood flow following a prolonged period of ischaemia results in irreversible tissue damage and myocardial dysfunction. Such ischaemic–reperfusion (I/R) injury occurs following myocardial infarction and is a risk in a number of surgical procedures, including coronary bypass and transplant surgery. Numerous studies have shown that ischaemic preconditioning (ip) is a powerful means of protecting the heart against this type of injury. This involves subjecting the heart to brief periods of ischaemia interspersed by periods of normal perfusion prior to prolonged ischaemia, and it has been shown to reduce myocardial cell death as well as having a number of other cardioprotective effects (Murry et al. 1986). Similar beneficial effects are produced by hypothermia, which is used in a number of surgical procedures to protect against an expected ischaemic insult (Riess et al. 2004). In a recent issue of The Journal of Physiology, Khaliulin et al. (2007) described the novel protocol of temperature preconditioning (TP), which combines the principles of ischaemic preconditioning and hypothermia. The study compared the effectiveness of TP with ip and delivery of a single hypothermic perfusion (SHP) in protecting the heart against I/R injury.

Temperature preconditioning of isolated rat hearts – a potent cardioprotective mechanism involving a reduction in oxidative stress and inhibition of the mitochondrial permeability transition pore

We investigate whether temperature preconditioning (TP), induced by short-term hypothermic perfusion and rewarming, may protect hearts against ischaemic/reperfusion injury like ischaemic preconditioning (IP). Isolated rat hearts were perfused for 40 min, followed by 25 min global ischaemia and 60 min reperfusion (37 degrees C). During pre-ischaemia, IP hearts underwent three cycles of 2 min global ischaemia and 3 min reperfusion at 37 degrees C, whereas TP hearts received three cycles of 2 min hypothermic perfusion (26 degrees C) interspersed by 3 min normothermic perfusion. Other hearts received a single 6 min hypothermic perfusion (SHP) before ischaemia. Both IP and TP protocols increased levels of high energy phosphates in the pre-ischaemic heart. During reperfusion, TP improved haemodynamic recovery, decreased arrhythmias and reduced necrotic damage (lactate dehydrogenase release) more than IP or SHP. Measurements of tissue NAD+ levels and calcium-induced swelling of mitochondria isolated at 3 min reperfusion were consistent with greater inhibition of the mitochondrial permeability transition at reperfusion by TP than IP; this correlated with decreased protein carbonylation, a surrogate marker for oxidative stress. TP increased protein kinase Cepsilon (PKCepsilon) translocation to the particulate fraction and pretreatment with chelerythrine (PKC inhibitor) blocked the protective effect of TP. TP also increased phosphorylation of AMP-activated protein kinase (AMPK) after 5 min index ischaemia, but not before ischaemia. Compound C (AMPK inhibitor) partially blocked cardioprotection by TP, suggesting that both PKC and AMPK may mediate the effects of TP. The presence of N-(2-mercaptopropionyl) glycine during TP also abolished cardioprotection, indicating an involvement of free radicals in the signalling mechanism.

Cardioprotection by temperature preconditioning is mediated by free radicals, PKC and AMPK activation

Cardioprotection by temperature preconditioning is mediated by free radicals, PKC and AMPK activation