This study examines the electrophysiological and metabolic changes that occur in rabbit hearts during hypothermic storage in vitro . Hearts were microperfused at 4°C for 6 or 24h with either normal Krebs-Henseleit buffer (KHB) or KHB containing 2,3-butanedione monoxime (BDM). After hypothermic storage, hearts were rewarmed to 37°C with KHB. Cardiac function was then assessed in Langendorff perfusion mode. Electrophysiological changes were also assessed from the ventricular paced-evoked responses. After storage, mitochondria were isolated from the hearts and their respiratory control ratio, rate of ATP synthesis and outer membrane intactness were assessed. Compared with values from fresh non-stored hearts, hearts stored hypothermically for 24h showed significant decreases in both left ventricular developed pressure and coronary flow when reperfused in Langendorff mode. On the other hand, the decrease in left ventricular developed pressure in hearts that were stored for only 6h (with or without BDM) was not significant. Compared with values obtained from fresh non-stored hearts, hypothermic storage significantly decreased the R-wave amplitude, and both the R-E and ST-E intervals of paced-evoked responses. This was true for hearts microperfused for 6h (with or without BDM) and for hearts microperfused with buffer containing BDM for 24h. The ST-R intervals in hearts microperfused hypothermically for 6h were prolonged, but this change was not statistically significant compared with those obtained from unstored hearts. In hearts microperfused with KHB containing BDM for 24h, the ST-R interval was significantly prolonged. Hypothermic microperfusion for 24h significantly decreased both the mitochondrial coupling ratio and the rate of ATP synthesis. In hearts microperfused with BDM for 6h, mitochondrial coupling ratios and the rate of ATP synthesis were not significantly different from those in fresh hearts. In conclusion, the present study has shown that long-term hypothermic storage significantly impaired both paced-evoked responses and mitochondrial function. Inclusion of BDM in the perfusion buffer during storage significantly ameliorated some of these changes.

1. This study examined the effects of altering nitric oxide levels with sodium nitroprusside or l -arginine in rat hearts stored hypothermically. 2. Hearts were microperfused at 4 ;°C for 24 ;h with a modified Krebs–Henseleit buffer (KHB) that contained either sodium nitroprusside, l -arginine, l -arginine methyl ester or dexamethasone. 3. After hypothermic storage, hearts were rewarmed to 37 ;°C with KHB alone or KHB containing sodium nitroprusside or l -arginine. Cardiac function was then assessed in either Langendorff mode or working heart mode. 4. Compared with values from fresh unstored hearts, hypothermic stored hearts showed a significant decrease in coronary flow and left ventricular developed pressure when the stored hearts were perfused in Langendorff mode. These hearts also produced less aortic flow and cardiac output when perfused in the working mode. 5. Hearts hypothermically microperfused with buffer containing either l -arginine or sodium nitroprusside and then reperfused in the Langendorff mode with untreated KHB buffer had the highest left ventricular developed pressure and coronary flow values. Aortic flow and cardiac output were also higher in these hearts. 6. In all groups of stored hearts, the concentrations of both ATP and creatine phosphate were significantly low, when compared with values from freshly isolated hearts. Addition of dexamethasone to the buffer either during storage or during reperfusion had no beneficial effect on high-energy phosphate loss or cardiac performance of stored hearts. 7. This study showed that the addition of nitric oxide donors to storage buffer significantly improves cardiac function on normothermic reperfusion. The improved functional recovery is unrelated to the high-energy phosphate content of these hearts.

1. This study examines the protective effect of staurosporine, chelerythrine, Ro 31-8220 and 2,3-butanedione monoxime in rat hearts during hypothermic storage. 2. Hearts were microperfused at 4°C for 24 or 48 h with a storage buffer that in some cases contained one of these protein kinase C inhibitors either alone or in combination with 2,3-butanedione monoxime. After hypothermic storage, hearts were rewarmed to 37°C with Krebs—Henseleit buffer. Cardiac function was then assessed in either Langendorff mode or working heart mode. 3. Compared with values from fresh non-stored hearts, hypothermic stored hearts showed a significant decrease in both coronary flow and left ventricular developed pressure when the stored hearts were reperfused in Langendorff mode. The decrease in coronary flow and left ventricular developed pressure was more pronounced in hearts stored for 48 h than in those stored for 24 h. 4. Hearts stored for 24 or 48 h, with or without the protein kinase C inhibitors, and then perfused in working mode generated less aortic flow and less cardiac output than fresh unstored hearts. 5. Hearts preserved in solutions containing staurosporine, chelerythrine, Ro 31-8220 or 2,3-butanedione monoxime had significantly higher left ventricular developed pressure values on reperfusion than hearts stored without any such drug. 6. Addition of 2,3-butanedione monoxime to a storage buffer containing either staurosporine, chelerythrine or Ro 31-8220 further improved left ventricular developed pressure, aortic flow and cardiac output values in these stored hearts. The group of hearts stored in a buffer containing 2,3-butanedione monoxime and chelerythrine gave the highest left ventricular developed pressure value seen during reperfusion. 7. The ATP and creatine phosphate concentrations of hearts stored in buffer alone were significantly lower than those of fresh unstored hearts, irrespective of the duration of storage. ATP concentrations were better preserved in hearts stored in a buffer containing 2,3-butanedione monoxime or/and one of the protein kinase C antagonists than those stored without such antagonists. A positive correlation was found between peak cardiac output values and the concentrations of combined high-energy phosphates in various groups of stored and reperfused hearts. 8. The present study showed that inhibition of protein kinase C during long-term hypothermic storage significantly increased high-energy phosphate concentrations and also improved contractile function during reperfusion.