Zhao-Nian Zhou

ATP-dependent potassium channels involved in the cardiac protection induced by intermittent hypoxia against ischemia/reperfusion injury

The aim of this study was to investigate the protection afforded by intermittent hypoxia (IH) against ischemia/reperfusion injury and its effects on calcium homeostasis during ischemia/reperfusion. The roles of KATP channels in these two actions were to be explored. Isolated hearts from IH and normoxic rats were subjected to 30 min global ischemia followed by 30 min reperfusion. Cardiac function was less deteriorated during ischemia and reperfusion in the IH rat hearts compared to normoxia rat hearts. Amplitude of the maximal contracture during ischemia was lower, while time to maximal contracture was extended in IH hearts. Post-ischemic recovery of left ventricular developed pressure and +/-dP/dtmax were higher in IH hearts than in normoxic hearts. KATP antagonist glibenclamide (10 microM) completely abolished these protective effects of IH, but had no appreciable influence on normoxic hearts. In cardiomyocytes isolated from normoxic hearts, [Ca2+]i, measured as arbitrary units of fluorescence ratio (340 nm/380 nm) of fura-2, gradually increased during 20 min simulated ischemia and kept at high level during 30 min reperfusion (1.081 +/- 0.004 and 1.088 +/- 0.006 respectively, p<0.01 vs pre-ischemia perfusion). However, in cardiomyocytes isolated from IH hearts, [Ca2+]i kept at normal level during ischemia and reperfusion (1.012 +/- 0.006 and 1.021 +/- 0.002 respectively, P>0.05 vs pre-ischemia perfusion). 10 microM glibenclamide and 100 microM 5-hydroxydecanoate (a selective mitochondria KATP antagonist) respectively abolished this effect of IH; calcium overloading reappeared during ischemia (1.133 +/- 0.007 and 1.118 +/- 0.007 respectively, P<0.01) and reperfusion (1.091 +/- 0.004 and 1.095 +/- 0.012 respectivly, P<0.01). However they had no effects on simulated ischemia and reperfusion-induced calcium overloading in normoxic myocytes. 50 microM pinacidil, a KATP opener, attenuated calcium overloading during ischemia and reperfusion in normoxic myocytes, but had no effect on [Ca2+]i change in IH myocytes. These results suggested that KATP channels contributed to the cardiac protection induced by IH against ischemia/reperfusion injury; the elimination of calcium overloading during ischemia/reperfusion by IH might underlie the mechanism of protection.

Effects of intermittent hypoxia on action potential and contraction in non-ischemic and ischemic rat papillary muscle.

Although it has been reported that intermittent hypoxia had the anti-arrhythmia effect, little is known about the effects on the action potential (AP) and contraction of papillary muscle, as well as the mechanism of anti-arrhythmia. The purpose of present study is to observe the effects of intermittent hypoxia on action potential and contraction of papillary muscle in rat left ventricle simultaneously using conventional intracellular microelectrode and contraction recording. The effects of intermittent hypoxia on AP and contraction during ischemic solution perfusion were also investigated. After exposed to intermittent hypoxia (six hours daily) for 42 days (IH42), duration (APD20) of 20%, 50% (APD50) and 90% (APD90) repolarization of AP prolonged significantly compared with animals in control (Con). Effective refractory period (ERP) in IH42 also prolonged significantly. Perfused with mimic ischemic solution, the changes of electric and mechanical activities in IH42 and in 28 days exposure to intermittent hypoxia (IH28) were much smaller than that in Con and IH14. The result of the study suggested that intermittent hypoxia prolonged the APD and ERP, offered the resistance against the ischemic damage on myocardium, which may be the electrophysiological basis of the anti-arrhythmia of intermittent hypoxia.

Proteomic analysis of mitochondrial proteins in cardiomyocytes from rats subjected to intermittent hypoxia

Intermittent hypoxia (IH) markedly enhances cardiac tolerance against ischemia/reperfusion injury, but its mechanism and molecular basis remain unclear. For exploring the expression of mitochondrial proteins induced by IH, two-dimensional electrophoresis and Thermo Finnigan LTQ mass spectrometer (MS) were applied. After comparing the protein profiles of myocardial mitochondria between IH and normoxic hearts, 14 protein spots were found to be altered more than threefold between the two groups, 11 of which were identified by Finnigan LTQ MS. Among these 11 proteins, 9 were involved in energy metabolism, including 7 that were increased after IH. The latter were identified as aldehyde dehydrogenase, methylmalonate-semialdehyde dehydrogenase, ATP synthase β chain, mitochondrial aconitase, malate dehydrogenase, electron transfer flavoprotein α subunit and sirtuin 5. Two other proteins, ubiquinol-cytochrome C reductase iron-sulfur subunit and aspartate aminotransferase, were decreased after IH. Biochemical tests for energy metabolism in mitochondria supported the proteomic results. IH exposure also increased the expression of a molecular chaperone—heat shock protein 60 and an antioxidant protein, peroxiredoxin 5. These findings will provide clues for understanding the mechanism of IH-induced cardiac protection and may lead to the development of interventional strategies designed to utilize the advantages of IH clinically.

Effects of Chronic Intermittent Hypobaric Hypoxia on the L-type Calcium Current in Rat Ventricular Myocytes

This study was conducted to investigate the role of the L-type calcium channel in the cardioprotection afforded by chronic intermittent hypobaric hypoxia (CIHH). Rats were exposed to CIHH for 28 days (CIHH28) or 42 days (CIHH42), respectively, before their ventricular myocytes were isolated for electrophysiological studies. Under normal recording conditions, no difference was found in the current density and voltage dependence of activation and inactivation of I(caL) recorded in CIHH28 and CIHH42 myocytes, compared with those in control myocytes isolated from rats exposed to sea-level air. Under simulated ischemic (I) conditions, the peak I(ca.L) decreased in all groups. However, the decreases of I(caL) in CIHH rats were of a lesser extent than those in the control. Simulated ischemia also induced an approximately 10-mV positive shift of the steady-state inactivation curve of I(caL) in control but not in CIHH myocytes, as measured by the half-maximal inactivation potentials (V(1/2)). The results suggest that adaptation to CIHH might have increased the tolerability of cardiac myocytes to ischemic challenges through preventing electrophysiological remodeling of the calcium channel.

Effect of intermittent and continuous hypoxia on ryanodine receptors of rat heart

Intermittent hypoxia (IH) adaptation has been shown to exert beneficial effects on the functions of hearts that had been subjected to insult by ischemia or ischemia/reperfusion. To understand whether calcium release channels/ryanodine receptors (RyRs) were involved, the effects of IH and continuous hypoxia (CH) on [3H]ryanodine binding to homogenates of rat hearts were investigated. Similar studies were performed on rat skeletal muscle. The main results on cardiac muscle were as follows: 1) Ischemia for up to 45 min in normal rat hearts had no obvious effect on the equilibrium ryanodine binding constant (K(d)), while the maximum number of ryanodine binding sites (B(max)) was affected in a time-dependent manner. B(max) was significantly increased with 15 min ischemia, which then returned to control levels upon prolonging the ischemia to 30 min. After 45 min ischemia, a small decrease of B(max) was observed. 2) IH adaptation for up to 28 days did not change B(max), but a significant decrease of B(max) was apparent after longer IH adaptation or after CH exposure. Although B(max) was not altered by 30 min ischemia, 30 min reperfusion following 30 min ischemia induced an evident decrease of B(max). After either IH or CH adaptation, the ischemia/reperfusion- induced decrease of B(max) was abolished. 3) Several effects on K(d) of ischemia and ischemia/reperfusion, with and without IH or CH adaptation, were observed. The most distinct and consistent finding was that a clear increase of K(d) was induced by ischemia or ischemia/reperfusion in CH adapted rats. [3H]Ryanodine binding to homogenates of rat skeletal muscle was also affected by IH and CH adaptation. In contrast to that found in cardiac muscle, a decrease of B(max) in skeletal muscle appeared only after CH adaptation. The physiological significance of these effects is discussed.

Circulating miRNAs from Dried Blood Spots are Associated with High Altitude Sickness

Circulating miRNAs isolated from dried blood spots (DBS) were found to be associated with high altitude sickness (HAS) patients in Tibet. HAS arises from two different diseases which are acute (AMS) and chronic (CMS) mountain sickness. Circulating miRNAs differences were found between AMS Han Chinese patients and normal Han controls and between CMS Tibetan Chinese patients and normal Tibetan controls. HAS arises from hypoxia which afflicts some high altitude inhabitants or visitors and not others. The difference results from each individual’s genetic makeup where hypoxia related genes have been shown to be a major contributor to these sicknesses. Several fold changes increases (up regulation) were found in the hypoxia associated miRNAs let-7f-5p, miR-9-5p, miR-19a-3p, miR-23a-3p, miR-98-5p, miR-125a-5p, miR-181b-5p, mir-202-3p, miR-372, miR-381-3p, miR-519d, miR-520d-3p, and miR-656 for both HAS groups compared to their controls. Other miRNAs (miR-19a-3p, 302c-3p and 875-3p) were found to be up regulated in one HAS group and down regulated in the other HAS group indicating the genetic differences between the two sickness groups.

SNPs, linkage disequilibrium, and chronic mountain sickness in Tibetan Chinese

Chronic mountain sickness (CMS) is estimated at 1.2% in Tibetans living at the Qinghai–Tibetan Plateau. Eighteen single-nucleotide polymorphisms (SNPs) from nine nuclear genes that have an association with CMS in Tibetans have been analyzed by using pairwise linkage disequilibrium (LD). The SNPs included are the angiotensin-converting enzyme (rs4340), the angiotensinogen (rs699), and the angiotensin II type 1 receptor (AGTR1) (rs5186) from the renin–angiotensin system. A low-density lipoprotein apolipoprotein B (rs693) SNP was also included. From the hypoxia-inducible factor oxygen signaling pathway, the endothetal Per-Arnt-Sim domain protein 1 (EPAS1) and the egl nine homolog 1 (ENGL1) (rs480902) SNPs were included in the study. SNPs from the vascular endothelial growth factor (VEGF) signaling pathway included are the v-akt murine thymoma viral oncogene homolog 3 (rs4590656 and rs2291409), the endothelial cell nitric oxide synthase 3 (rs1007311 and rs1799983), and the (VEGFA) (rs699947, rs34357231, rs79469752, rs13207351, rs28357093, rs1570360, rs2010963, and rs3025039). An increase in LD occurred in 40 pairwise comparisons, whereas a decrease in LD was found in 55 pairwise comparisons between the controls and CMS patients. These changes were found to occur within and between signaling pathways, which suggests that there is an interaction between SNP alleles from different areas of the genome that affect CMS.