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1.
Brain metabolism and intracellular pH were studied during and after episodes of ischaemia and hypoxia-ischaemia in lambs anaesthetised with sodium pentobarbitone. 31P and 1H magnetic resonance spectroscopy methods were used to monitor brain pHi and brain concentrations of Pi, phosphocreatine (PCr), beta--nucleoside triphosphate (beta NTP), and lactate. Simultaneous measurements were made of cerebral blood flow and cerebral oxygen and glucose consumption. Cerebral ischaemia sufficient to reduce oxygen delivery to 75% of control values was associated with a fall in brain pHi and increase in brain Pi. Progressively severe hypoxia-ischaemia was associated with a progressive fall in brain pHi, PCr, and beta NTP and increase in brain Pi. In two animals the increase in brain lactate during hypoxia-ischaemia measured by 1H nuclear magnetic resonance (NMR) could be quantitatively accounted for by the increased net uptake of glucose by the brain in relation to oxygen, but was insufficient to account for the concomitant acidosis according to previous estimates of brain buffering capacity. In four animals brain pHi, PCr, Pi, and beta NTP had returned to normal 1 h after the hypoxic-ischaemic episode. In one animal brain pHi had reverted to normal at a time when 1H NMR indicated persistent elevation of brain lactate.  相似文献   

2.
Hypoxic pretreatment is known to induce anoxia tolerance in plant species sensitive to oxygen deprivation. However, we still do not have detailed information on changes in cytoplasmic and vacuolar pH (pHcyt and pHvac) in plants under low-oxygen availability (hypoxia) and under anoxia. To investigate this, we have studied the influence of hypoxia and anoxia on pHcyt and pHvac, glucose-6-phosphate (Glc-6-P) and nucleotide triphosphate (NTP) contents in rice ( Oryza sativa L.) root tips in comparison with those of wheat ( Triticum aestivum L.) with in vivo 31P-nuclear magnetic resonance. Both cereals responded to hypoxia similarly, by rapid cytoplasmic acidification (from pH 7.6–7.7 to 7.1), which was followed by slow partial recovery (0.3 units after 6 h). Anoxia led to a dramatic pHcyt drop in tissues of both species (from pH 7.6–7.7 to less than 7.0) and partial recovery took place in rice only. In wheat, the acidification continued to pH 6.8 after 6 h of exposure. In both plants, NTP content followed the dynamics of pHcyt. There was a strong correlation between NTP content and cytoplasmic H+ activity ([H+]cyt= 10−pHcyt) for both hypoxic and anoxic conditions. Glc-6-P content increased in rice under anoxia and hypoxia. In wheat, Glc-6-P was not detectable under anoxia but increased under hypoxia. In this study, rice root tips were shown to behave as anoxia tolerant tissues. Our results suggest that the initial cytoplasmic acidification and subsequent pHcyt are differently regulated in anoxia tolerant and intolerant plants and depend on the external oxygen concentration.  相似文献   

3.
Changes in high-energy phosphate metabolites and the intracellular pH (pHi) were monitored in cerebral tissue during periods of hypoglycaemia and hypoxia using 31P nuclear magnetic resonance spectroscopy. Superfused brain slices were loaded with deoxyglucose at a concentration shown not to impair cerebral metabolism, and the chemical shift of the resulting 2-deoxyglucose-6-phosphate (DOG6P) peak was used to monitor the pHi. In some experiments with low circulating levels of Pi, the intracellular Pi was visible and indicated a pH identical to that of DOG6P, an observation validating its use as an indicator of pHi in cerebral tissue. The pHi was found to be unchanged during moderate hypoglycaemia; however, mild hypoxia (PO2 = 16.4 kPa) and severe hypoglycaemia produced marked reductions from the normal of 7.2 to 6.8 and 7.0, respectively. Hypoglycaemia caused a fall in the level of both phosphocreatine (PCr) and ATP, whereas hypoxia affected PCr alone, as shown previously. However, the fall in pHi was similar during the two insults, thus indicating that the change in pH is not directly linked to lactate production or to the creatine kinase reaction.  相似文献   

4.
We measured cerebral phosphocreatine (PCr), inorganic phosphate (Pi), ATP, and intracellular pH (pHi) with in vivo phosphorus nuclear magnetic resonance (NMR) during 10- to 15-min periods of reversible hypoxic hypoxia in 20 newborn lambs (1-11 days). There was a significant correlation between arterial O2 partial pressure (PaO2) and the PCr/Pi ratio or pHi; however, between PaO2 130-33 mmHg, metabolite changes were not significant. PCr/Pi and pHi decreased significantly when PaO2 was lowered below 33 and 28 mmHg, respectively. After recovery, metabolite ratios and pHi returned to base-line values within 5 min. During the early phases of hypoxia and recovery, there were large fluctuations in metabolites and pHi, indicating that mitochondrial reactions were not in a steady state. After several minutes of hypoxia or recovery, PCr/Pi and pHi stabilized, suggesting steady state kinetics for mitochondrial respiration. NMR is extremely sensitive to changes in mitochondrial oxygenation, and stable PCr/Pi and pHi indicate that O2 tension in cerebral mitochondria of the newborn lamb is constant between PaO2 of 30 and 140 mmHg.  相似文献   

5.
Oxygen consumption (o2) and respiratory variables were measured in the Prochilodontid fish, Prochilodus scrofa exposed to graded hypoxia after changes in temperature. The measurements were performed on fish acclimated to 25°C and in four further groups also acclimated to 25°C and then changed to 15, 20, 30 and 35°C. An increase in o2 occurred with rising temperature, but at each temperature o2 was kept constant over a wide range of O2 tensions of inspired water ( Pi o2). The critical oxygen tensions ( Pc o2) were Pi o2= 22 mmHg for 25°C acclimated specimens and after transfer from 25°C to 15, 20, 30 and 35°C the Pc o2 changed to Pi o2= 28, 22, 24 and 45 mmHg, respectively. Gill ventilation ( G ) increased or decreased following the changes in o2 as the temperature changed and was the result of an accentuated increase in breath frequency. During hypoxia the increases in G were characterized by larger increases in breath volume. Oxygen extraction was kept almost constant at about 63% regardless of temperature and ambient oxygen tensions in normoxia and moderate hypoxia ( P o2∼70 mmHg). P. scrofa showed high tolerance to hypoxia after abrupt changes in temperature although its survival upon transfer to 35°C could become limited by the capacity of ventilatory mechanisms to alleviate hypoxic stress.  相似文献   

6.
Egg jelly induces the degradation of histones as well as the acrosome reaction in the spermatozoa of Asterina pectinifera . Much similar degradation of histones without any apparent morphological changes such as the acrosome reaction was induced in the spermatozoa by merely dispersing them into Na+-free seawater. It required external Ca2+ much less than the jelly-induced one in normal seawater, and was not susceptible to Ca2+-channel antagonists, verapamil and diltiazem. Once spermatozoa were incubated with egg jelly in Ca2+-free seawater, they did not undergo the histone degradation even after subsequent addition of Ca2+, but Na+-free seawater rescued such blockage. Spontaneous acrosome reaction occurred in seawater containing 10–30 mM Na+ in a Ca2+-dependent manner. This reaction was accompanied by a rapid increase in intracellular pH (pHi) followed by a large pHi decrease. Diltiazem blocked a large decrease in pHi but scarcely inhibited the acrosome reaction induced by low-Na+ seawater. Increasing K+ inhibited both pHi changes and the acrosome reaction induced by low-Na+ seawater. Decreasing pH of seawater also inhibited the pHi changes but did not affect the acrosome reaction. Strontium was also effective to induce a rapid increase, followed by a gradual decrease, in pHi and the acrosome reaction.  相似文献   

7.
In cultured cells derived from micromeres isolated at the 16-cell stage of sea urchin embryos, the activity of H+, K+-ATPase became detectable after 15 hr of culture, when the cells started to form spicules, and then increased reaching a plateau from 25 hr of culture. The Na+, K+-ATPase activity of isolated micromeres increased to a maximum at 20 hr of culture and thereafter decreased gradually. Allylisothiocyanate, an inhibitor of H+, K+-ATPase, caused a decrease in intracellular pH (pHi) accompanied by blockage of 45Ca deposition in spicule rods in spicule-forming cells at 30 hr of culture. Ouabain and amiloride had scarcely any effect on the pHi or 45, deposition. In cultured cells exposed to nifedipine, which blocked 45Ca deposition in spicule rods, allylisothiocyanate did not cause any decrease in pHi. These results show that H+, which is generated in the overall reaction to produce CaCO3 from Ca2+ and HCO3, is probably released from the cells mainly in the reaction catalyzed by H+, K+-ATPase to maintain successive production of CaCO3.  相似文献   

8.
Brain metabolism and intracellular pH were studied during and after episodes of incomplete cerebral ischaemia in lambs under sodium pentobarbitone anaesthesia. 31P and 1H magnetic resonance spectroscopy was used to monitor brain pHi and brain concentrations of inorganic phosphate (Pi), phosphocreatine (PCr), beta-nucleoside triphosphate (beta NTP), and lactate. Simultaneous measurements were made of arterio-cerebral venous concentration differences (AVDs) for oxygen, glucose, and lactate. Cerebral ischaemia was induced by a combination of bilateral carotid clamping and hypotension, and the acute effects of systemic administration of glucose and sodium bicarbonate were examined. The molar ratio of glucose to oxygen uptake by the brain (6G/O2) increased above unity during cerebral ischaemia. Statistically significant AVDs for lactate were not observed. Cerebral ischaemia was associated with a reduction in brain pHi PCr/Pi ratio, and an increase in brain lactate. No effect of arterial plasma glucose on brain lactate concentration or brain pHi was evident during cerebral ischaemia or in the postischaemic period. Administration of sodium bicarbonate systemically in the postischaemic period was associated with a rise in arterial and brain tissue PCO2. A fall in brain pHi occurred which was attributable in part to coincidental brain lactate accumulation. The increase in brain lactate measured by 1H nuclear magnetic resonance in vivo during ischaemia was insufficient to account for the change in buffer base calculated to have occurred from previous estimates of brain buffering capacity.  相似文献   

9.
When sperm of the sea urchin, Hemicentrotus pulcherrimus , were exposed to high pH (9.0) sea water, they showed large increases in intracellular Ca2+ ([Ca2+]i) and pH (pHi) and underwent the acrosome reaction (AR) without the aid of the egg jelly. Not only [Ca2+]i increase but also pHi rise did not occur under Ca2+-free conditions. Both the increases in [Ca2+]i and pHi and the AR by high pH were inhibited by a Ca2+ channel blockers, verapamil and nisoldipine, and by a lectin, wheat germ agglutinin (WGA) which interacts with a 220 kD membrane glycoprotein of sperm. These reagents inhibited also the AR by the egg jelly. The inhibitory effects of WGA were immediately canceled by the addition of N-acetyl-D-glucosamine, a sugar which is known to remove WGA from its binding site. These results suggest that 1) the same Ca2+ transport system is activated by high external pH and the egg jelly, 2) increase in [Ca2+]i is prerequisite for the stimulation of the H+-efflux system(s) and 3) the 220 kD WGA-binding membrane protein functions as a regulator protein of Ca2+ transport system.  相似文献   

10.
丹参对心肌低氧/复氧损伤的保护作用的研究   总被引:7,自引:0,他引:7  
目的:研究中药丹参(SM)对心肌低氧/复氧损伤的保护作用。方法:运用^31P-NMR技术对离体灌流大鼠心脏的高能磷酸化合物含量及细胞内的pH值(pHi)进行动态跟踪。结果:丹参注射液能明显减轻低氧期间心肌高能磷酸合物含量的下降,促使复氧期间PCr、ATP相对含量的恢复,减少低氧及复氧阶段心肌pHi的下降。结论:丹参参改善低氧及复氧期间心肌能量代谢水平,减轻心肌低氧/复氧损伤,并能显著改善细胞内酸碱  相似文献   

11.
31P nuclear magnetic resonance (NMR) spectroscopy was used to estimate the amount of inorganic phosphate (Pi) present in the cytoplasm and vacuole of root tips and subapical root segments of pond pine ( Pinus serotina Michx.). In root tips of seedlings grown with 100 mmol m–3P (HP) the cytoplasmic Pi content, on a root volume basis, was ≈ 1·5 μ mol cm–3 and the vacuolar Pi content, on a root volume basis, was ≈ 3·4 μ mol cm–3. In root tips from Pi starved seedlings the cytoplasmic Pi content, on a root volume basis, was ≈ 0·75 μ mol cm–3; vacuolar Pi was too low to be reliably estimated. Similar results were obtained with subapical root segments; the Pi concentration in the cytoplasm was maintained at around 2 mol m–3 while that in the vacuole varied with Pi supply. This work demonstrates for the first time that quantitative measurements of the subcellular compartmentation of Pi can be made in young tissues of a woody species. The results indicate that cytoplasmic Pi levels are maintained across a range of external Pi supplies probably by withdrawing Pi stored in the vacuole.  相似文献   

12.
Abstract: We have used the human sympathetic neuronal line SH-SY5Y to investigate the effects of hypoxia on noradrenaline (NA) release evoked by either raised [K+]o (100 m M ) or the nicotinic acetylcholine receptor (nAChR) agonist dimethylphenylpiperazinium iodide (DMPP). NA release was monitored by loading cells with [3H]NA and collecting effluent fractions from perfused cells kept in a sealed perifusion chamber. Cells were challenged twice with either stimulus and release was expressed as that evoked by the second challenge as a fraction of that evoked by the first. K+-evoked release was unaffected by hypoxia (P o 2≅ 30–38 mm Hg), but release evoked by DMPP was significantly increased. For both stimuli, replacement of Ca2+o with 1 m M EGTA abolished NA release. K+-evoked release was also dramatically reduced in the presence of 200 µ M Cd2+ to block voltage-gated Ca2+ channels, but DMPP-evoked release was less affected. In hypoxia, DMPP-evoked Cd2+-resistant NA release was dramatically increased. Our findings indicate that hypoxia increases NA release evoked from SH-SY5Y cells in response to nAChR activation by increasing Ca2+ influx through the nAChR pore, or by activating an unidentified Cd2+-resistant Ca2+-influx pathway. As acetylcholine is the endogenous transmitter at sympathetic ganglia, these findings may have important implications for sympathetic activity under hypoxic conditions.  相似文献   

13.
The concentrations of intra-erythrocytic adenylates (ATP, ADP and AMP) and guanylates (GTP, GDP and GMP) were determined in rainbow trout subjected to 10% blood removal every 12 h for 96 h. Haemoglobin concentration, [Hb], decreased from 6·043±0·617 to 0·957 ± 0·195 g dl−1. This decrease in [Hb] was followed by a continuous increase in total organic phosphates, e.g. adenylates plus guanylates. Intra-erythrocytic NTP (ATP plus GTP) levels increased significantly after 48 h when haemoglobin concentration was 2·427 ± 0·256 g dl−1. Although a significant increase in GDP levels in animals with [Hb] less than 1·677 ± 0·235 g dl−1 was observed, the general increase in guanylate level was mainly due to the GMP which increased about 85-fold during the experimental period. It is suggested that the erythrocytes of anaemic rainbow trout have the capacity to increase NTP/Hb4 ratios which may represent an advantage for anaemic fish.  相似文献   

14.
Maize ( Zea mays L. Hybrid Sweet Corn, Royal Crest), a C4 plant, was grown under different light regimes, after which the rate of photosynthesis and activities of several photosynthetic enzymes (per unit leaf chlorophyll) were measured at different light intensities. Plants were grown outdoors under direct sunlight or 23% of direct sunlight, and in growth chambers at photosynthetic photon flux densities of about 20% and 8% of direct sunlight. The plants grown under direct sunlight had a higher light compensation point than plants grown under lower light. At a light intensity about 25% of direct sunlight, plants from all growth regimes had a similar rate of photosynthesis. Under saturating levels of light the plants grown under direct sunlight had a substantially higher rate of photosynthesis than plants grown under the lower light regimes. The higher photosynthetic capacity in the plants grown under direct sunlight was accompanied by an increased activity of several photosynthetic enzymes and in the amount of the soluble protein in the leaf. Among five photosynthetic enzymes examined, RuBP carboxylase (EC 4.1.1.39) and pyruvate, Pi dikinase (EC 2.7.9.1) were generally just sufficient to account for rates of photosynthesis under saturating light; thus, these may be rate limiting enzymes in C4 photosynthesis. Pyruvate, Pi dikinase and NADP-malate dehydrogenase (EC 1.1.1.82) were the only enzymes examined which were light activated and increased in activity with increasing light intensity. In the low light grown plants the activity of pyruvate, Pi dikinase closely paralleled the photosynthetic rate measured under different light levels. With the plants grown under direct sunlight, as light intensity was increased the activation of pyruvate, Pi dikinase and NADP+-malate dehydrogenase proceeded more rapidly than photosynthesis.  相似文献   

15.
A comparative study of blood oxygen binding and carrying capacities of turbot Scophthalmus maximus and sea bass Dicentrarchus labrax , two fish species differing in their demand for oxygen, was carried out under three levels of chronic hypoxia ( P o 2 = 93, 65 and 40 mmHg) for 40 days. Blood O2 affinity in normoxia was moderately high in both species ( P 50 was c . 12–13 mmHg at pH 7·7). The Bohr factor was significantly lower in turbot (−0·52) than in sea bass (−0·85). In both species, blood O2 affinity was not significantly affected by oxygen depletion whatever its level and duration. In turbot, however, P 50 appeared to slightly decrease at the two more severe levels of hypoxia. In both species, blood O2 carrying capacity was not affected by hypoxia and remained twice as high in sea bass than in turbot.  相似文献   

16.
Trout fitted with arterial catheters were subjected to 6 min of strenuous exercise, injected with either saline (controls) or the β-adrenergic antagonist propranolol, and monitored over the following 8-h recovery period. Control responses were very similar to those previously reported, except for much higher resting and post-exercise plasma catecholamine levels, and less marked RBC pHi regulation, perhaps due to season (February–May). Trout subjected to prior β-blockade would not exercise. Trout β-blocked immediately after exercise showed a much higher incidence of mortality during the recovery period, but accompanying symptoms were similar to those previously documented in control trout dying after exercise. Specific effects of post-exercise β-blockade seen in both survivors and mortalities were a sustained elevation of arterial Pco2 and an inhibition of blood glucose elevation. There were negligible effects on RBC pHi and volume regulation, blood metabolic acid and lactate dynamics, or plasma ion changes. The results provide little support for the hypothesis that β-adrenergic actions of plasma catecholamines are intimately involved in post-exercise recovery, but must be considered in the context of the 'winter' trout, where β-responses may be diminished.  相似文献   

17.
Atlantic salmon Salmo salar with amoebic gill disease (AGD) were exposed to a graded hypoxia (135–40 mmHg water P O2) and blood samples analysed for respiratory gases and pH at 119, 79·5 and 40 mmHg water P O2. There were no differences in the rate of oxygen uptake between infected and control fish. However, arterial P O2, and pH were significantly lower in the infected fish whereas P CO2 was significantly higher in infected fish compared with controls prior to hypoxia and at 119 mmHg water P O2. At 79·5 and 40 mmHg water P O2 saturation, there were no significant differences in blood P O2 or pH although blood P CO2 was elevated in AGD affected fish at 50% hypoxia (79·5 mmHg water P O2). The elevated levels of P CO2 in fish affected by AGD resulted in a persistent respiratory acidosis even during hypoxic challenge. These data suggest that even though the fish were severely affected by AGD, the presence of AGD while impairing gas transfer under normoxic conditions, did not contribute to respiratory failure during hypoxia.  相似文献   

18.
低氧预处理对低氧/复氧心肌能量代谢的作用   总被引:4,自引:0,他引:4  
目的:研究低氧预处理(HPC)对心肌的保护作用,方法:借助^31P-NMR图谱技术,在模拟Langendorff离体灌流大鼠心脏的正常生理条件下,跟踪心肌高能磷酸化合物含量的动态变化。结果:在30min低氧期,PCr、ATP相对含量及PCr/Pi值逐渐减小,但HPC组减小的速度比对照组慢;而在复氧期,HPC组能提高心肌高能磷酸化合物含量的恢复程度,特别是复氧初期,HPC组PCr 、ATP相对含量及PCr/Pi值立即有了恢复;在本实验中,HPC对pHi的改善不显著。结论:HPC能降低后续长时间低氧及复氧阶段的心肌能量代谢,对心肌的低氧/复氧损伤具有保护作用。  相似文献   

19.
Phosphorus translocation in salt-stressed cotton   总被引:6,自引:0,他引:6  
The effect of salinity on plants has usually been studied at high inorganic P concentration ([Pi]) in the nutrient solution, and salinity × Pi interactions have been examined at much higher [Pi] than found in soil solutions. Short-term 32Pi experiments were carried out to study the effect of salinity (150 m M NaCl) on phosphorus translocation in cotton plants ( Gossypium hirsutum L. cv. Acala SJ-2) grown in nutrient solutions containing 10 μ M [Pi]. The effect of additional Ca to a concentration of 10 μ M was also tested. Salinity inhibited 32P translocation from root to shoot. This inhibition was more evident at higher [Pi] in the root medium. Increasing [Pi] 33-fold in the solution resulted in a 4.3-fold increase in [32P] in the root under saline conditions, but only in a 1,8-fold increase in the shoot. In older shoot tissues total [P] was elevated in the salinized plants. In the young tissues, however, total P concentration was higher in control plants. Inhibition of 32P translocation by salinity was greater from root to young leaves than to mature shoot tissues. Salinity also decreased 32P recirculation from the cotyledons to the young leaf. Inhibition by salinity of both 32P translocation and recirculation to young leaves was fully reversed by increasing Ca supply from 1 to 10  相似文献   

20.
Previous studies on the interaction between environmental inorganic phosphate (Pi) and salinity stress using soybean cultivars sensitive to high external Pi had two limitations: (1) the phenotype was dominated by overaccumulation of phosphorus (P); and (2) no detailed analysis was performed for sodium ion uptake. In this study, we focused on the effects of high external Pi on the sodium ion uptake in 'Pi-tolerant' soybean cultivars. The P accumulation in Pi-tolerant soybean Union was much lower [9.0 mg g1 dry weight (DW); contrasting to 38–76 mg g1 DW in the 'Pi-sensitive' soybean cultivars]. At in planta level, high level of external Pi significantly ( P  < 0.001) increased net sodium ion uptake and aggravated salinity stress symptoms. The effects of high external Pi diminished when de-rooted plants were used, suggesting that root is the primary organ interacting with Pi in the growth medium. Two-cell models, including soybean suspension cells and the tobacco Bright Yellow-2 cell line, were also employed to study the effects of high external Pi at the cellular level. Consistent to in planta results, high external Pi uplifted cellular sodium ion uptake and reduced cell viability under salinity stress. Gene expression analyses further showed that HPi (2 m M Pi supplements; excessive level of Pi) could reduce the fold of induction of GmSOS1 and GmCNGC under salinity stress, suggesting that they may be possible molecular targets involved in the interaction between high external Pi and Na+ uptake.  相似文献   

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