Regulation Of Intermittent Hypoxia On Myocardial [Na～+]i And [Ca～(2+)]i Against Ischemia/reperfusion Insult

The aim of this study was to investigate the cardiac protection afforded by intermittent hypoxia (IH) against ischemia/reperfusion (I/R) insult and its underlying mechanisms in rat heart. The main results are as follows: Isolated hearts from IH and control rats were subjected to 30 min global ischemia followed by 30 min reperfusion, recovery of cardiac function after ischemia was improved by IH. Cardiac myocytes isolated from IH and control rat hearts were exposed to 20 min simulated ischemia followed by 30 min reperfusion, increases in [Na+]i during I/R was significantly inhibited by IH, and the increase in [Ca2+]i was completely inhibited by IH. The improved cardiac function after I/R by IH was accompanied by an elevated preservation of the activity of Na+/K+-ATPase. Pretreatment with ouabain, a specifc inhibitor of Na+/K+-ATPase, abolished the effect of IH on [Na+]i and [Ca2+]i overload during simulated I/R and resulted in [Ca2+] overload. In control hearts, ischemia had no obvious effect on the equilibrium ryanodine binding constant (Kd), while the maximum number of ryanodine binding sites (Bmax) was significantly increase with ischemia, which then return to control levels after reperfusion. IH did not affect Kd , but inhibited the decrease of Bmax induced by I/R. Compared with control hearts, a significant increase of Bmax was observed in after I/R in IH hearts. KATP antagonist glibenclamide eliminated the beneficial effects of IH on recovery of cardiac function after ischemia, but had no influence on control hearts. Simulated 英文摘要6 I/R induced an significant overload of [Na+]i and [Ca2+]i in control cardiac myocytes, but did not affect [Ca2+]i in IH cardiomytes. Glibenclamied and 5-HD, selective mitochondrial KATP antagonist respectively abolished this effect of IH; [Ca2+]i overload reappeared during I/R. Pinacidil, a KATP opener attenuated [Ca2+]i overload during simulated I/R in control cardiac myoctes, but had no effect on [Ca2+]i change in IH myocytes. Curve of percentage of cell with KATP channel current in 20 min versa intracellular concentration of ATP ([ATP]i) was drawn with patch clamp of whole cell configure, [ATP]i was manipulated by adding K2ATP into pipette solution. IH shifted the curve upward and increase the concentration for half maximal effects (EC50) to 502 uM while EC50 in control cardiomyocytes was nearly 299uM, suggesting that KATP channel in IH cardiomyocytes can be activated at higher [ATP]i, however, KATP channel in control cardiomyocytes is still unactivated at similar level of [ATP]i. Compared with control cardiomyocytes, more cells with KATP channel current recorded were observed in IH cardiomyocytes perfused with a slow simulated ischemic solution for 20 min. About 75% IH cadiomyocytes with KATP channel current was shown, however 37.5% control cardiomyocytes with KATP channel current was observed. The concentation of Kir 6.1 mRNA coding for KATP channel was downregulated by IH, however, the concentration of Kir 6.1 mRNA were maintained well during ischemia/reperfusion in IH hearts than that in CON hearts. Chelerythrine, a specific inhibitor of PKC, blocked the improved recovery of cardiac function after ischemia by IH. Cherelerythrine also inhibited or even deteriorated the protective effect of IH on ionic homeostasis during simulated I/R. More serious ionic overload was observed in the cardiomyocytes treated with chelerythrine during ischemia. The translocation from cytosolic fraction to memb rane fraction is crucial for activation of the isoform of PKC. IH enhanced , to membrane fraction. translocations of PKC α , and We concluded that IH protected the hearts against I/R injury, improved the recovery of cariac function after I/R, inhibited [Na+] and [Ca2+] overload induced by simulated I/R. Better preservation of Na+/K+-ATPase, afciliated activation of KATP channels, PKC activation and translocation participated the cardioprotective effects afforded by IH.