[Effects of acute hypobaric hypoxia and exhaustive exercise on AMP-activated protein kinase phosphorylation in rat skeletal muscle].

The present study was aimed to explore the changes of phosphorylated AMP-activated protein kinase (pAMPK) level in skeletal muscle after exposure to acute hypobaric hypoxia and exhaustive exercise. Thirty-two male Sprague-Dawley (SD) rats were randomly divided into sea level and high altitude groups. The rats in high altitude group were submitted to simulated 5 000 m of high altitude in a hypobaric chamber for 24 h, and sea level group was maintained at normal conditions. All the rats were subjected to exhaustive swimming exercise. The exhaustion time was recorded. Before and after the exercise, blood lactate and glycogen content in skeletal muscle were determined; AMPK and pAMPK levels in skeletal muscle were detected by Western blot. The results showed that the exhaustion time was significantly decreased after exposure to high altitude. At the moment of exhaustion, high altitude group had lower blood lactate concentration and higher surplus glycogen content in gastrocnemius compared with sea level group. Exhaustive exercise significantly increased the pAMPK/AMPK ratio in rat skeletal muscles from both sea level and high altitude groups. However, high altitude group showed lower pAMPK/AMPK ratio after exhaustion compared to sea level group. These results suggest that, after exposure to acute hypobaric hypoxia, the decrement in exercise capacity may not be due to running out of glycogen, accumulation of lactate or disturbance in energy status in skeletal muscle.

Hypoxic training increases metabolic enzyme activity and composition of alpha-myosin heavy chain isoform in rat ventricular myocardium.

Cardiac muscle adaptation is essential for maintaining physical capacity after ascending to high altitude. This study examines the effects of high altitude training on myocardial metabolic enzyme activity and composition of alpha-myosin heavy chain (MHC). Rats were randomly divided into normobaric sedentary (NS) and training (NT) groups, and hypobaric sedentary (HS) and training (HT) groups. HS and HT rats were exposed to hypobaric hypoxia (simulated 4,000-5,000 m) for 5 weeks (24 h/day), and HT rats simultaneously received swim training. Hypoxia exposure for 5 weeks led to a decrease in succinate dehydrogenase (SDH) and citrate synthase (CS) activities in the left ventricle (LV), and a decrease in CS, hexokinase (HK) and total lactate dehydrogenase (LDH) activities in the right ventricle (RV) (p < 0.05, HS vs. NS). Furthermore, 1 h/day swim training during hypoxia exposure enhanced the CS activity in LV and the SDH and CS activities in RV (p < 0.05, HT vs. HS). The percentages of alpha-MHC in both ventricles in HT were higher than those in HS (p < 0.05). We conclude that exercise training at high altitude is beneficial for cardiac muscle adaptation to hypoxia by increasing activities of enzymes and percentage of alpha-MHC. This may contribute to improved cardiac function and work capacity at high altitude.

[Hypoxia promotes apoptosis of germ cells in rat testes].

OBJECTIVE: To explore the effects of hypobaric hypoxia on the apoptosis of germ cells in male rats. METHODS: Adult male Wistar rats were randomly divided into four groups: a control group raised at sea level; a 5 d, a 15 d and a 30 d hypoxic group raised in a hypobaric chamber simulating 5000 m altitude for 5 days, 15 days and 30 days respectively. Flow cytometry and TUNEL were used to evaluate the apoptosis of germ cells in the testis. Bax and Bcl-2 in the testis were measured by Western blot. RESULTS: Seminiferous tubules with apoptotic germ cells were significantly more in the hypoxic groups than in the control (P < 0.01). Most apoptotic germ cells were spermatogonia and spermatocytes. Compared with the control group, apoptotic germ cells detected by PI flow cytometry were significantly increased in the hypoxic 15 d and 30 d groups (P < 0.05); Bax was significantly higher (P < 0.05), and so was the ratio of Bax to Bcl-2 in the hypoxic 30 d group (P < 0.01). CONCLUSION: Hypoxia promotes apoptosis of testicular germ cells in male rats. Chronic hypoxia increases Bax expression in the rat testis.

[Isolation and identification of differentially expressed proteins in hippocampus of mice during hypobaric hypoxic delayed preconditioning].

AIM: To explore the differentially expressed proteins between hypobaric hypoxic delayed preconditioning (HHDP) and normal mouse hippocampus. METHODS: After the animal model of HHDP was constructed, hippocampal proteins were obtained by a series of abstraction with lysis solution containing high concentration urea. As soon as isoelectric focusing and SDS-PAGE was performed. The resolved proteins in the 2-DE gels were visualized by Coomassie blue R-250. The gels were scanned, and the images were processed with PDQuest software. Differential proteins were exactly excised from the gels, destained and digested with trypsin. The peptides were isolated and sent for MALDI-TOF-MS testing. Database searching was performed using peptide masses obtained from MALDI-TOF-MS. RESULTS: Averages of 481 +/- 38 and 477 +/- 21 protein spots were detected in control gels and preconditioning gels, respectively. 169 +/- 6 protein spots were matched between these two types of gels. Among the matched spots, while the quantities of 21 +/- 12 spots in control gels increased by above 2 times than that in preconditioning one, the quantities of 33 +/- 10 spots in preconditioning gels increased by the same times than that in control one. The correlation coefficient between these two patterns were 0.7748 +/- 0.0267. 12 spots in preconditioning gels significantly increased compared with the control (P < 0.05, n = 4). Among 12 spots excised from the gels, perfect peptide mass fingerprinting spectrums of 8 spots were acquired. The results showed that one protein was fructose biphosphate aldolase A. Three proteins matched nothing might be new proteins. The other four proteins just matched the partial sequences of the proteins of database were no coincidence to it's isoelectric point and molecular weight. So they might be homological proteins. CONCLUSION: Many proteins, for example fructose biphosphate aldolase A, has been differentially expressed in hippocampus of mice during HHDP. This may be one of the molecule mechanisms of HHDP.

[Effects of ATP concentration and hypoxic exposure on RNA and protein synthesis activity in isolated mitochondria from rat brain].

To explore the effects of ATP concentration in the medium and hypoxia exposure on mitochondrial DNA expression at transcriptional and translational level, rats were exposed to hypoxia in a hypobaric chamber simulating 4000 m above sea level for 3 d (acute hypoxia) or 40 d (chronic hypoxia). Cerebral cortex mitochondria were isolated from control and hypoxia-exposed rats by centrifugation program. The activities of intramitochondrial RNA and protein synthesis were measured respectively by the methods of incorporation of (3)H-UTP or (3)H-Leucine in a cell-free system in vitro in isolated organelle. The effect of different ATP concentrations in medium on incorporation activity of mitochondria from control rat brains was observed. The results showed that there was a 40% reduction in RNA synthesis and a 60% inhibition in protein synthesis in isolated mitochondria in vitro in acute hypoxia exposure compared to control. But in chronic hypoxic exposure, the inhibition of both RNA synthesis and protein synthesis was alleviated, being 72% and 76% of the normoxic control, respectively. Furthermore, the effect of ATP concentration in medium on mitochondrial RNA and protein synthesis in vitro showed two phases. The mitochondrial RNA and protein synthesis were inhibited when ATP concentration was either above or below 1 mmol/L in the incubation medium. These results indicate that hypoxia exposure affects the expression of mtDNA at both transcription and translation levels. It also suggests that the improvement of mitochondrial semi-automation during chronic hypoxic exposure may be at least one of the cellular mechanisms of body adaptation to hypoxia. The regulation of ATP in mitochondrial RNA and protein synthesis is therefore an economic and effective mode of regulation.

[Protein synthesis and characterization in isolated mitochondria from rat brain].

AIM: To establish a system of mitochondrial translation in vitro of rat brain and identify it's production of protein by molecular weight. METHODS: Mitochondria isolated from hemisphere of rat brain by differential centrifugations. The optimization of mitochondrial translation in vitro by 3H-Lencine incorporation was explored. 35S-methionine labeled products of mitochondrial protein synthesis were identified by SDS-PAGE and fluorography. RESULTS: Isolated mitochondria had a highly activity oxidative phosphorylation and respiratory control ratio (RCR) was between 3.5 and 5.5. The activity of 3H-Lencine incorporation in isolated mitochondria in vitro increased with time of incubation in 60 min and maintained a steady level. The maximal activity of 3H-Lencine incorporation per milligram mitochondria protein occured at 1 mg mitochondria/ml of incubation mix.The major auto radiographic bands could be observed at 86, 68, 56, 43, 33, 29, 25 and 18(kD) molecular weight separated on SDS-PAGE. CONCLUSION: The translation system of rat brain mitochondria in vitro is faithful and high activity, can be used to study mtDNA expression and regulation in mammalian brain at the level of translation.