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1.
Levine, Benjamin D., and James Stray-Gundersen."Living high-training low": effect of moderate-altitudeacclimatization with low-altitude training on performance.J. Appl. Physiol. 83(1): 102-112, 1997.The principal objective of this study was to test the hypothesisthat acclimatization to moderate altitude (2,500 m) plus training atlow altitude (1,250 m), "living high-training low," improvessea-level performance in well-trained runners more than an equivalentsea-level or altitude control. Thirty-nine competitive runners (27 men,12 women) completed 1) a 2-wklead-in phase, followed by 2) 4 wkof supervised training at sea level; and3) 4 wk of field training camprandomized to three groups: "high-low"(n = 13), living at moderate altitude(2,500 m) and training at low altitude (1,250 m); "high-high"(n = 13), living and training atmoderate altitude (2,500 m); or "low-low"(n = 13), living and training in amountain environment at sea level (150 m). A 5,000-m time trial was theprimary measure of performance; laboratory outcomes included maximalO2 uptake(O2 max), anaerobic capacity (accumulated O2 deficit),maximal steady state (MSS; ventilatory threshold), running economy,velocity at O2 max, and blood compartment volumes. Both altitude groups significantly increased O2 max(5%) in direct proportion to an increase in red cell mass volume(9%; r = 0.37, P < 0.05), neither of which changedin the control. Five-kilometer time was improved by the field trainingcamp only in the high-low group (13.4 ± 10 s), in directproportion to the increase inO2 max(r = 0.65, P < 0.01). Velocity atO2 max andMSS also improved only in the high-low group. Four weeks of livinghigh-training low improves sea-level running performance in trainedrunners due to altitude acclimatization (increase in red cell massvolume and O2 max) and maintenance of sea-level training velocities, mostlikely accounting for the increase in velocity atO2 max and MSS. 相似文献
2.
Thermal Characteristics of C4 Photosynthetic Enzymes from Leaves of Three Sugarcane Species Differing in Cold Sensitivity 总被引:2,自引:0,他引:2
Phosphoenolpyruvate carboxylase, NADP-malate dehydrogenase andNADP-malic enzyme in desalted extracts from the leaves of threesugarcane species differing in cold sensitivity were relativelystable at cold temperatures, and their Arrhenius plots appearedas straight lines. Pyruvate,Pi dikinase (PPDK) from the threespecies was cold-inactivated, and its Arrhenius plots exhibiteda clear break-point around 10.6°C. Analysis of cold labilityof PPDK using deuterium oxide and Triton X-100 showed that theinteractions between the subunits possibly involve hydro-phobicbonds which would lead to cold lability. There were no apparentdifferences among the three sugarcane species in the thermalproperties of the four C4 photosynthetic enzymes. The resultssuggest that the differences in cold sensitivity of sugarcanephotosynthesis may not relate to the thermal properties of C4photosynthetic enzymes per se.
1 Present address: Department of Biochemistry, University ofNebraska, Lincoln, NE 68588-0664, U.S.A. 相似文献
3.
Tonoplast and plasma membrane vesicles were prepared from chilling-sensitive(CS) and chilling-insensitive (CI) cultured cells of rice (Oryzasativa L.) to examine how they would respond to low temperature.With CS cells, the specific activity of ATPase in tonoplastvesicles was relatively higher than that of plasma membraneATPase. Tonoplast ATPase activity was decreased by low temperaturetreatment, and a slight decrease in plasma membrane ATPase activitywas also observed. The decrease in the specific activity ofthe tonoplast ATPase by low temperature may reflect a decreasein Vmax. However, no change was noted in Km. The break pointof the Arrhenius plots of the tonoplast ATPase was ca. 32?C,this value being ca. 9?C higher than that of the plasma membraneATPase. With CI cells, the specific activity of tonoplast ATPasewas somewhat less than that of the plasma membrane ATPase. TonoplastATPase activity was decreased by low temperature at 5?C, whereasan increase in plasma membrane ATPase activity was observed.The break point of the tonoplast ATPase activity was ca. 22?C,which was 3?C higher than that of the plasma membrane ATPase.Using ATPase solubilized from the plasma membrane or tonoplast,the Arrhenius plots of log ATPase activity against the reciprocalof absolute temperature gave a straight line fit from 5?C to45?C with no obvious break point. The break point appeared onadding a phospholipid mixture (asolectin) to a reaction mixturecontaining solubilized enzyme. The slope of the curve of theArrhenius plot was very different between the CS and CI cells.The plasma membrane and tonoplast ATPases from the CS cellshad a higher Ea above 20?C, whereas that from the CI cells hada lower one. These findings indicate that the tonoplast ATPase in a riceplant is more sensitive to low temperature than the plasma membraneATPase, with this response possibly being due to interactionsbetween the proteins and phospholipids. (Received January 6, 1988; Accepted July 5, 1988) 相似文献
4.
Shelp, B. J. 1987. Plant characteristics and nutrient compositionand mobility of broccoli (Brassica oleracea var. italica) suppliedwith NH+4, NO3 or NH4NO3.J. exp. Bot. 38: 16031618. The effects of varying NH+4, NO3 or NH4NO3 concentration onthe final plant characteristics, element composition, and accumulationof NO3-N, NH+4-N and organic-N were evaluated in broccoli (Brassicaoleracea var. italicacv. Futura and Premium Crop) plants culturedin vermiculite under greenhouse conditions supplemented withlight. NH+4-grown plants were stunted and exhibited signs ofmarginal necrosis on the old leaves, accompanied by an accumulationof NH4. The tissue levels of N, P, Mn, Cu, Zn and B were generallyincreased by NH+4 versus NO3 nutrition whereas the reverse wastrue for Ca; Mg and K were only slightly affected, if at all.These results are attributed to: changes in element availabilityresulting from reduced rhizosphere pH due to NH+4uptake ratherthan NO 3uptake; competition of Ca uptake by NH+4; and dilutionof N by increased vegetative growth with NO3-nutrition. Theelement concentrations of N, P or K were similar in all tissueswhereas Ca, B and Mn were markedly less in the florets and youngleaves compared to mature leaves; this supports literature indicatingthat the former elements are phloem-mobile whereas the latterare not. Assuming that the nutrient supply for mature leavesis delivered principally via the xylem stream, the data suggestthat nutrients for developing leaves and florets are suppliedpredominantly in the phloem. If so, under our experimental conditions.Zn and Cu were also readily mobile in the phloem whereas Mgmovement was restricted. NH4+ versus NO4+ J nutrition alteredthe distribution of these elements. The two broccoli cultivarstested under the greenhouse environment differed in NH+4 toleranceand in the distribution of K and Cu suggesting there was a geneticbasis for cultivar variation in mineral acquisition and redistribution. Key words: Plant nutrition, phloem mobility, elemental composition. 相似文献
5.
The effect of root temperature and form of inorganic nitrogensupply on in vitro nitrate reductase activity (NRA) was studiedin oilseed rape (Brassica napus L. cv. bien venu). Plants weregrown initially in flowing nutrient solution containing 10 µMNH4NO3 and then supplied with either nitrate or ammonium for15 d at root temperatures of 3, 7, 11 or 17 °C. Shoot temperatureregime was similar for all plants; 20/15 °C, day/night.Root NRA was highest when roots were grown at 3 and 7 °C.In laminae and petioles NRA was highest when roots were 11 or17 °C. The plants supplied with ammonium had much lowerlevels of NRA in roots after 5 d than the plants supplied onlywith nitrate. NRA in the laminae of plants supplied with ammoniumwas low relative to that in plants supplied with nitrate onlywhen root temperature was 11 or 17 °C. Values of the apparent activation energy (Ea) of NR, calculatedfrom the Arrhenius equation, in laminae and petioles were differentfrom roots suggesting difference in enzyme conformation. Evidencethat the temperature at which roots were growing affected Eawas equivocal. Oilseed rape, Brassica napus L., activation energy, ammonium, Arrhenius equation, nitrate, root temperature, nitrate reductase 相似文献
6.
The light-induced recovery of cell division and chloroplastdevelopment in "giant", "bleached" cells of the Emerson strainof Chlorella is unaffected by treatments (atrazine. CMU, incubationin a CO2-free atmosphere) which interfere with photosynthesis.Anaerobic conditions or the presence of respiratory inhibitors(DNP, KCN, NaN3) markedly suppress recovery. Recovery is accompaniedby a mobilization of the reserve starch which follows a linearcourse over the first 9 hr. Chloramphenicol (50 µg/ml),which inhibits chlorophyll synthesis and the development ofa photosynthetic capacity, is without effect on the early rateof starch mobilization. Evidence is presented that the contributionof photosynthesis towards recovery is only significant whenthe reserve starch has been depleted. Recovery does not requirecontinuous light; the critical light-stimulated processes apparentlytaking place during the first 9 hr. The possible nature of thelight stimulation of recovery is discussed. (Received June 18, 1973; ) 相似文献
7.
The feeding behaviour of two freshwater zooplankton species,the calanoid copepod Eudiaptomus gracilis and the cladoceranDaphnia longispina, at extremely low food concentrations hasbeen studied in order to test whether the animals react as predictedby the models of optimal foraging. Three different sized algae were offered in concentrations downto 1µg C/litre at 7°C during winter and 19°C duringsummer. Ingestion rates were measured by use of a flow-through14C-technique In contrast to the findings of several authors working withmarine copepods a threshold concentration where the animalsceased filtering could be detected only in one experiment byregression analysis (Daphnia, 19°C, food: Stichococcus).A depression of the filtering rate at low concentrations wasobserved only in Daphnia at 19°C with Stichococcus and Scenedesmusas food. It is supposed that in this case the reduction of thefiltering rate is not a direct response of the filtrator, butis caused by exhaustion due to the experimental conditions. As freshwater zooplankton is very rarely exposed to food abundancesas low as in the marine environment, there seems to be no selectionpressure favouring the evolution of an "optimal forager" behaviour.
(1)Supported by Deutsche Forschungsgemeinschaft 相似文献
8.
Changes in photosynthetic carbon metabolism during the glucosebleaching of Chlorella protothecoides cells were investigatedusing NaH14CO3 as tracer. Several hours after incubating thegreen algal cells in the glucose medium in the dark, the ratesof 14C-incorporation into glucose polymers and sucrose decreasedand the incorporation into the lipid fraction (fatty acids)greatly increased. At this stage, the rate of photosynthetic14CO2 fixation and the chlorophyll content were practicallythe same as in the starting green cells. Afterwards, the photosyntheticcapacity and chlorophyll content continued to decrease throughoutthe experimental period. In contrast, when photosynthetic 14CO2fixation of green cells was carried out in the medium containingglucose, the rate of 14C-incorporation into glucose polymersincreased, though there was no change in the incorporationsinto sucrose and the lipid fraction.
1Part of this investigation was reported at the Conference "ComparativeBiochemistry and Biophysics of Photosynthesis" (Japan-U.S. CooperativeScience Program) held at Hakone, Japan in 1967.
2Present address: Faculty of Agriculture, Tamagawa University,Machida-shi, Tokyo, Japan. (Received June 10, 1974; ) 相似文献
9.
A Mathematical Model to Utilize the Logistic Function in Germination and Seedling Growth 总被引:5,自引:1,他引:4
Several models have been proposed to describe germination rates,but most are limited in statistical analysis and biologicalmeaning of indices. Therefore, a mathematical model is proposedto utilize the logistic function. The function was defined asan overall response including time, temperature, and the interactionbetween time and temperature. Cumulative germination percentagesover time were used to develop the model. Germination tests were conducted on indiangrass (Sorghastrumnutans (L.) Nash) strain IG-2C-F1, at constanttemperatures of 9, 12, 15, 20, 25, and 30 °C. The functionfitted the observed data over six temperatures at r2 = 0.99.Time to reach 10% of final germination (Gt10) increased from2.5 d at 30 °C to 44.0 d at 9 °C, and Gt50 (time toreach 50% of final germination) increased from 3.6 d at 30 °Cto 53.8 d at 9 °C. True germination rate (% d1) foreach temperature was maximum at Gt50. A linear model of 1/Gt50versus temperature was used to estimate the base temperatureof 8.3 °C for germination. An Arrhenius plot indicated achange occurred between 20 °C and 25 °C for temperatureresponse of germination. Published data on hypocotyl growthof Cucumis melo L. were recalculated using the model. Absolutegrowth rates showed a temperature response similar to the publishedweighted-mean elongation rates. Base temperature for hypocotylgrowth of C. melo was estimated as 8.8 °C. The proposedmodel proved to be useful in calculating and interpreting germinationand growth kinetics. Key words: Indiangrass, Sorghastrum nutans (L.) Nash, Germination rate, Threshold temperature, Arrhenius plot, Growth rate, Cucumis melo L 相似文献
10.
Shelp, B. J. 1987. The composition of phloem exudate and xylemsap from broccoli (Brassica oleracea var. italica) suppliedwith NH+4, NO3 or NH4NO3.J. exp. Bot. 38: 16191636. The detailed composition of xylem sap and exudate from stemincisions of attached inflorescences of broccoli (Brassica oleraceavar. italica) was compared in plants supplied with NH+4, NO3or NH4NO3. A phloem origin for the exudate was suggested fromthe high levels of sugars (71133 mg cm-3), amino acids(8·1-26·7 mg cm3) and K. (2·33·8mg cm3), the low levels of NO3 and Ca, the high C: N (w/w) ratios(8·333), and the alkaline pH (7·27·3).In contrast, the xylem sap was mildly acidic (pH 5·66·0),and possessed lower levels of all organic and inorganic solutesbut NO3 and Ca, and lower ratios of K: Ca, Mg: Ca and C: N (0·64·4). Glutamine was the predominant o-phthalaldehyde-reactive aminocompound in both transport fluids with the next most abundantamino acids dependent on sap type and N-form. Together witharginine, -aminobutyric acid, which was found only in the xylemstream, was enhanced by NH+4compared to NO3 -nutrition suggestingthat glutamate metabolism was stimulated in the roots. Underlimiting N the amino acid concentrations in the transport fluidswere greater with NH+4 than with NO3. NO3 reduction occurredin both the root and shoot with the latter site predominatingover the entire N range (0-300 mol m3). Even though the compositionof nitrogenous solutes in the xylem was dependent on cultivarand N source, the composition of the phloem streams supplyingthe developing inflorescence was relatively unaffected. The data on the element composition of organs and phloem sapare interpreted to suggest that, in spite of the restrictedmobility of some elements such as B and Mn, a significant proportionof their total supply to developing sinks is carried in thephloem stream. Key words: Transport fluid composition, plant nutrition, phloem mobility. 相似文献
11.
Oxygenconsumption (O2)was measured in normoxia as ambient temperature(Ta) was lowered from 40 to15°C, at the rate of 0.5°C/min (thermoneutrality ~33°C).In 2-day-old rats born in hypoxia after hypoxic gestation, theTa-O2relationship was as in controls; their interscapular brown adiposetissue (IBAT) was hypoplastic (less proteins and DNA), with lowerconcentration of the mitochondrial uncoupling proteinthermogenin. In 8-day-old rats exposed to hypoxiapostnatally (day 2 today 8), at anyTa below thermoneutralityO2 was higher than incontrols; also, in this group IBAT was hypoplastic with decreasedthermogenin. Additional measurements under variousexperimental conditions indicated that the increased thermogeniccapacity was not explained by the smaller body mass and increased bloodoxygen content or by the eventuality of intermittent cold stimuliduring the chronic hypoxia. On the other hand, chronic hypercapnia (3%CO2 in normoxia, fromday 2 to day8) also resulted in increased normoxic thermogenesis. We conclude that chronic hypoxia in the perinatal period1) reduces IBAT mass andthermogenin concentration and2) can increase the newborn's thermogenic capacity because of stress-related mechanisms not specific to hypoxia. 相似文献
12.
- As previously demonstrated, normal cells of Chlorella protothecoidesare bleached with degeneration of chloroplasts when they areincubated, under aerobic conditionseither in the lightor in darkness, in a glucose-containing medium withoutadded nitrogen source ("glucose-bleaching"). It was found inthe present study that under the atmosphere of N2, neither bleachingnor growth of algal cells occurs in the dark, while in the lighta significant growth of cells takes place with formation ofa certain amount of chlorophyll.
- Studies on the effects ofvarious inhibitors (ammonium ion,DNP, CMU, -hydroxysulphonates,arsenate, cyanide, azide, andantimycin A) under different conditionsshowed that oxidativephosphorylation is a necessary processfor the occurrence ofthe glucosebleaching as well as the assimilationof glucose(cellular growth). Under light-anaerobic conditionsin the presenceof glucose, assimilation of glucose (cellulargrowth) takesplace being supported by photophosphorylation,but no bleachingoccurs.
- When the algal cells in the courseof bleaching were transferredto the glucose-free mineral medium,the cell growth ceased immediatelybut the cell bleaching proceededfor several hours before itscessation. The respiratory activity,which was high in the glucose-containingmedium, became loweron transferring the algal cells into theglucose-free medium.The lowered level of respiration was maintained,for more than8 hr after the transfer of cells to the glucose-freemedium.
- When the cells in the course of bleaching were placed underthe atmosphere of N2, the cell bleaching ceased almost instantaneously.
- Based on these observations and other inhibition experiments,it was inferred that a certain intermediate(s) produced by theaerobic respiration of glucose is closely associated with theoccurrence of cell bleaching, and that an O2-requiring stepmay be involved in the process of chlorophyll degradation.
13.
The relativelyrecent detection of nitric oxide (NO) in the exhaled breath hasprompted a great deal of experimentation in an effort to understand thepulmonary exchange dynamics. There has been very little progress intheoretical studies to assist in the interpretation of the experimentalresults. We have developed a two-compartment model of the lungs in aneffort to explain several fundamental experimental observations. Themodel consists of a nonexpansile compartment representing theconducting airways and an expansile compartment representing thealveolar region of the lungs. Each compartment is surrounded by a layerof tissue that is capable of producing and consuming NO. Beyond thetissue barrier in each compartment is a layer of blood representing thebronchial circulation or the pulmonary circulation, which are bothconsidered an infinite sink for NO. All parameters were estimated fromdata in the literature, including the production rates of NO in the tissue layers, which were estimated from experimental plots of theelimination rate of NO at end exhalation (ENO) vs. theexhalation flow rate (E). The modelis able to simulate the shape of the NO exhalation profile and tosuccessfully simulate the following experimental features of endogenousNO exchange: 1) an inverse relationship between exhaled NOconcentration and E, 2) the dynamic relationship between the phase III slope andE, and 3) the positiverelationship between ENO andE. The model predicts that theserelationships can be explained by significant contributions of NO inthe exhaled breath from the nonexpansile airways and the expansilealveoli. In addition, the model predicts that the relationship betweenENO and E can be used as anindex of the relative contributions of the airways and the alveoli toexhaled NO. 相似文献
14.
The cell-membrane resistance (Rm) of Vigna hypocotyls was examined,and the effects of osmotic stress, ionic stress and IAA on Rmwere investigated. Rm decreased by 64 to 77% under osmotic stressin the presence of absorbable solutes (40 mM sorbitol, 15 mMKC1, 30 mM sucrose; or 40 mM sorbitol, 15 mM KC1, 30 mM sucroseplus 104 M IAA) or under ionic stress (50 mM NaCl or50 mM KC1). Rm was not changed by perfusion with 104M IAA. Therefore, the hyper-polarizations of the membrane potentialobserved in both cases should be ascribed totally to the activationof the electrogenic proton pump. Although Rm showed an increaseof 1.6 fold when the hypocotyls were subjected to osmotic stress(100 mM sorbitol or 100 mM sorbitol plus 104 M IAA),83.6% or 92.4% of the hyperpolarization of the membrane potential(Vpx was also the result of the activation of the pump. Theresults, calculated on the basis of the current source model,support the viewpoint that the hyperpolarization of the cellmembrane potential of Vigna hypocotyls under osmotic stress,ionic stress or in the presence of IAA is an expression of theactivation of the proton pump, and is not caused by an increasein Rm.
1 Present address: Researchers and Planners of Natural Environment, Yotsugi Bldg. (2F), 1-5-4 Horinouchi, Suginami-Ku, Tokyo,166 Japan
2 Present address: Graduate School of Integrated Science, YokohamaCity University, 22-2 Seto, Kanazawa-Ku, Yokohama, 236 Japan (Received February 14, 1991; Accepted July 24, 1991) 相似文献
15.
The photosynthetic electron transport and phosphorylation reactions were measured in the room temperature region in the thylakoid membranes prepared from the blue-green alga, Anacystis nidulans. The Arrhenius plot of the Hill reaction with 2,6-dichlorophenolindophenol showed a distinct break of straight lines at 21°C in the membranes from cells grown at 38°C, and at 12°C in those from cells grown at 28°C. The Arrhenius plot of the Hill reaction with ferricyanide showed a break at 13°C in the membranes from cells grown at 38°C, and at 7°C in those from cells grown at 28°C. On the other hand, the Arrhenius plot of the System I reaction with methylviologen as an electron acceptor and 2,6-dichlorophenolindophenol and ascorbate as an electron donor system was composed of a straight line in the membranes from cells grown at 28°C as well as at 38°C. The Arrhenius plot of the System II reaction measured by the ferricyanide reduction mediated by silicotungstate in the presence of 3-(3′,4′-dichlorophenyl)-1,1-dimethylurea also showed a break at 11°C in the membranes from cells grown at 38°C.The Arrhenius plot of the phosphorylation mediated by N-methylphenazonium methylsulfate showed a break at 21°C in the membranes from cells grown at 38°C and at 12°C in those from cells grown at 28°C. The Arrhenius plot of the phosphorylation mediated by the System I reaction showed a break at 24°C in the membranes from cells grown at 38°C.The characteristic features in the Arrhenius plots of the photosynthetic electron transport and phosphorylation reactions are discussed in terms of the transition of physical phase of the thylakoid membrane lipids. 相似文献
16.
DNA synthesis in the light perturbation period and its relationto the reappearance, due to light perturbation, of once faded-out"light interruption rhythm" in a long-day duckweed, Lemna gibbaG 3, were studied. After long continuous darkness, the duckweedincorporated 3H-thymidine into both nuclear and satellite DNAsunder a light condition, but into satellite DNA alone undera dark condition. The number of dividing cells in frond epidermisincreased in proportion to the length of the light perturbationperiod. This increase was inhibited by 5-fluorodeoxyuridine.From these and previous results we conclude that nuclear DNAnewly synthesized in the light is intimately related with thereappearance of the rhythm. (Received June 15, 1970; ) 相似文献
17.
Gautier, Henry, Cristina Murariu, and Monique Bonora.Ventilatory and metabolic responses to ambient hypoxia orhypercapnia in rats exposed to CO hypoxia. J. Appl. Physiol.83(1): 253-261, 1997.We have investigated at ambienttemperatures (Tam) of 25 and5°C the effects of ambient hypoxia(Hxam; fractional inspired O2 = 0.14) and hypercapnia(fractional inspiredCO2 = 0.04) on ventilation (),O2 uptake(O2), andcolonic temperature (Tc) in 12 conscious rats before and after carotid body denervation (CBD). Therats were concomitantly exposed to CO hypoxia (HxCO; fractional inspired CO = 0.03-0.05%), which decreases arterial O2 saturation by ~25-40%.The results demonstrate the following. 1) AtTam of 5°C, in both intact andCBD rats,/O2 islarger when Hxam orCO2 is associated withHxCO than with normoxia. At Tam of 25°C, this is also thecase except for CO2 in CBD rats. 2) AtTam of 5°C, the changes inO2 andTc seem to result from additiveeffects of the separate changes induced byHxam,CO2, andHxCO. It is concluded that, inconscious rats, central hypoxia does not depress respiratory activity.On the contrary, particularly whenO2 is augmented during acold stress, both/O2during HxCO and the ventilatoryresponses to Hxam andCO2 are increased. The mechanismsinvolved in this relative hyperventilation are likely to involvediencephalic integrative structures. 相似文献
18.
Aluminium Effects on ATPase Activity and Lipid Composition of Plasma Membranes in Sugar Beet Roots 总被引:3,自引:1,他引:2
The effect of aluminium (Al) in vivo and in vitro on root plasmamembranes has been studied in two sugar beet (Beta vulgarisL.) cultivars, Monohill (Al-sensitive) and Regina (relativelyAl-tolerant). Although Al in vitro inhibited the MgATPase inan uncompetitive way for both cultivars raised in the absenceof Al, the specific K+-activation of the MgATPase was only inhibitedby Al in cv. Monohill. Arrhenius analysis of the MgATPase activity showed that theeffect of Al in vitro depended on whether or not the plantswere exposed to Al in vivo. Al treatment in vitro of the MgATPasefrom control plants cultivated at a low pH (5·4) causedan increase in the phase transition temperature from 17 to 22°C. Only at a higher pH range (pH 6·1) could a secondtransition temperature be induced (at 9 °C). By additionof Al in vitro to plants cultivated with Al at pH 5·4,the slopes of the activity plots did not change. Aluminium changedthe Km of the ATPase for MgATP in an opposite way by treatmentin vivo and in vitro. Lipid analyses of the plasma membranes showed that the acylcomposition differed little following Al treatment in vivo,but that the ratio of phosphatidylcholine: phosphatidylethanolamineincreased. The changes correlated with the observed change inthe Km for the MgATPase. We conclude that the main effect ofAl on the MgATPase is not due to the formation of an Al-ATPcomplex. Instead, Al may bind to the membrane-bound enzyme(s)and/or modify the lipid environment. Key words: Aluminium, ATPase, Beta vulgaris, lipids 相似文献
19.
Rohlicek C. V.; Saiki C.; Matsuoka T.; Mortola J. P. 《Journal of applied physiology》1998,84(3):763-768
We questioned whether the decrease inO2 consumption(O2) during hypoxia innewborns is a regulated response or reflects a limitation inO2 availability. Experiments wereconducted on previously instrumented conscious newborn dogs.O2 was measured at a warmambient temperature (30°C, n = 7)or in the cold (20°C, n = 6),while the animals breathed air or were sequentially exposed to 15 minof fractional inspired O2(FIO2): 21, 18, 15, 12, 10, 8, and 6%. In normoxia,O2 averaged 15 ± 1 (SE)and 25 ± 1 ml · kg1 · min1in warm and cold conditions, respectively. In the warmcondition, hypometabolism (i.e., hypoxicO2 < normoxicO2) occurred at FIO2 10%, whereas in thecold condition, hypometabolism occurred atFIO2 12%. The sameresults were obtained in a separate group(n = 14) of noninstrumented puppies.For all levels of FIO2 withhypometabolism, the relationships between measures ofO2 availability (arterialO2 saturation or content, venousPO2 or saturation,x-axis) vs.O2(y-axis) had lower slopes in warm than in coldconditions. Hence, O2 during hypometabolism in the warm condition was not the maximal attainable for the level of oxygenation. The results do not support thepossibility that the hypoxic drop inO2 in the newborn reflects a limitation in O2availability. The results are compatible with the ideathat the phenomenon is one of "regulated conformism" tohypoxia. 相似文献
20.
Acute hypoxia selectively inhibits KCNA5 channels in pulmonary artery smooth muscle cells 总被引:2,自引:0,他引:2
Platoshyn O Brevnova EE Burg ED Yu Y Remillard CV Yuan JX 《American journal of physiology. Cell physiology》2006,290(3):C907-C916
Acute hypoxia causes pulmonary vasoconstriction in part by inhibiting voltage-gated K+ (Kv) channel activity in pulmonary artery smooth muscle cells (PASMC). The hypoxia-mediated decrease in Kv currents [IK(V)] is selective to PASMC; hypoxia has little effect on IK(V) in mesenteric artery smooth muscle cells (MASMC). Functional Kv channels are homo- and/or heterotetramers of pore-forming -subunits and regulatory -subunits. KCNA5 is a Kv channel -subunit that forms functional Kv channels in PASMC and regulates resting membrane potential. We have shown that acute hypoxia selectively inhibits IK(V) through KCNA5 channels in PASMC. Overexpression of the human KCNA5 gene increased IK(V) and caused membrane hyperpolarization in HEK-293, COS-7, and rat MASMC and PASMC. Acute hypoxia did not affect IK(V) in KCNA5-transfected HEK-293 and COS-7 cells. However, overexpression of KCNA5 in PASMC conferred its sensitivity to hypoxia. Reduction of PO2 from 145 to 35 mmHg reduced IK(V) by 40% in rat PASMC transfected with human KCNA5 but had no effect on IK(V) in KCNA5-transfected rat MASMC (or HEK and COS cells). These results indicate that KCNA5 is an important Kv channel that regulates resting membrane potential and that acute hypoxia selectively reduces KCNA5 channel activity in PASMC relative to MASMC and other cell types. Because Kv channels (including KCNA5) are ubiquitously expressed in PASMC and MASMC, the observation from this study indicates that a hypoxia-sensitive mechanism essential for inhibiting KCNA5 channel activity is exclusively present in PASMC. The divergent effect of hypoxia on IK(V) in PASMC and MASMC also may be due to different expression levels of KCNA5 channels. membrane potential; potassium channels; vascular smooth muscle 相似文献