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1.
Jones  M. B.  Humphries  S. W. 《Hydrobiologia》2002,488(1-3):107-113
Fluxes of CO2 and H2O vapour were measured by eddy covariance from a stand of the C4 emergent sedge Cyperus papyrus (papyrus), which formed a fringing swamp on the north-west shore of Lake Naivasha, Kenya. The fluxes of CO2 and H2O vapour between the papyrus swamp and the atmosphere were large but variable, depending on the hydrology of the wetland system and the condition of the vegetation. These measurements, combined with simulation modelling of annual fluxes of CO2, show that papyrus swamps have the potential to sequester large amounts of the carbon (1.6 kg C m–2 y–1) when detritus accumulates under water in anaerobic conditions, but they are a net source of carbon release to the atmosphere (1.0 kg C m–2 y–1) when water levels fall to expose detritus and rhizomes to aerobic conditions. Evapotranspiration from papyrus swamps (E) was frequently lower than evaporation from open water surfaces (E o) and plant factors have a strong influence on the flux of water to the atmosphere. For the period of measurement E/Eo was 0.36.  相似文献   

2.
Summary We have chosen the MDCK cell line to investigate aldosterone action on H+ transport and its role in regulating cell membrane K+ conductance (G m K ). Cells grown in a monolayer respond to aldosterone indicated by the dose-dependent formation of domes and by the alkalinization of the dome fluid. The pH sensitivity of the plasma membrane K+ channels was tested in giant cells fused from individual MDCK cells. Cytoplasmic pH (pH i ) andG m K were measured simultaneously while the cell interior was acidified gradually by an extracellular acid load. We found a steep signoidal relationship between pH i andG m K (Hill coefficient 4.4±0.4), indicating multiple H+ binding sites at a single K+ channel. Application of aldosterone increased pH i within 120 min from 7.22±0.04 to 7.45±0.02 and from 7.15±0.03 to 7.28±0.02 in the absence and presence of the CO2/HCO 3 buffer system, respectively. We conclude that the hormone-induced cytoplasmic alkalinization in the presence of CO2/ HCO 3 is limited by the increased activity of a pH i -regulating HCO 3 extrusion system. SinceG m K is stimulated half-maximally at the pH i of 7.18±0.04, internal H+ ions could serve as an effective intracellular signal for the regulation of transepithelial K+ flux.  相似文献   

3.
Summary We investigated intracellular pH (pH i ) regulation in cultured human ciliary muscle cells by means of the pH-sensitive absorbance of 5(and 6)-carboxy-4,5-dimethylfluorescein (CDMF). The steady-state pH i was 7.09±0.04 (n = 12) in CO2/ HCO 3 -buffered and 6.86±0.03 (n = 12) in HEPES-buffered solution. Removal of extracellular sodium for 6 min acidified the cells by 1.11±0.06 pH units (n = 12) in the presence of CO2/ HCO 3 and by 0.91±0.05 pH units (n = 8) in its absence. Readdition of external sodium resulted in a rapid pH i recovery, which was almost completely amiloride-sensitive in the absence of CO2/ HCO 3 but only slightly influenced by amiloride in its presence. Application of DIDS under steady-state conditions significantly acidified the ciliary muscle cells by 0.25±0.02 (n = 4) in 6 min, while amiloride had no effect. The pH i recovery after an intracellular acid load was completely dependent on extracellular sodium. In HEPES-buffered solution the pH i recovery was almost completely mediated by Na+/H+ exchange, since it was blocked by amiloride (1 mmol/liter). In contrast, a marked amilorideinsensitive pH i recovery was observed in CO2/HCO 3 -buffered solution which was mediated by chloride-independent and chloride-dependent Na+ HCO 3 cotransport. This recovery, inhibited by DIDS (0.2 mmol/liter). was also observed if the cells were preincubated in chloride-free solution for 4 hr. Analysis of the sodium dependence of the pH i recovery after NH4Cl prepulse revealed V max = 0.57 pH units/min, K m= 39.7 mmol/liter extracellular sodium for the amiloride-sensitive component and V max = 0.19 pH units/min, K m= 14.3 mmol/liter extracellular sodium for the arniloride-insensitive component. We conclude that Na+/H+ exchange and chloride-independent and chloride-dependent Na+HCO 3 cotransport are involved in the pH i regulation of cultured human ciliary muscle cells.The expert technical assistance of Astrid Krolik is gratefully acknowledged. This work was supported by the Deutsche Forschungsgemeinschaft grant DFG Wi 328/11.  相似文献   

4.
H2 oxidation,O2 uptake and CO2 fixation in hydrogen treated soils   总被引:2,自引:0,他引:2  
Dong  Z.  Layzell  D.B. 《Plant and Soil》2001,229(1):1-12
In many legume nodules, the H2 produced as a byproduct of N2 fixation diffuses out of the nodule and is consumed by the soil. To study the fate of this H2 in soil, a H2 treatment system was developed that provided a 300 cm3 sample of a soil:silica sand (2:1) mixture with a H2 exposure rate (147 nmol H2 cm–3hr–1) similar to that calculated exist in soils located within 1–4 cm of nodules (30–254 nmol H2 cm–3hr–1). After 3 weeks of H2 pretreatment, the treated soils had a Km and Vmax for H2 uptake (1028 ppm and 836 nmol cm–3 hr–1, respectively) much greater than that of control, air-treated soil (40.2 ppm and 4.35 nmol cm–3 hr–1, respectively). In the H2 treated soils, O2, CO2 and H2 exchange rates were measured simultaneously in the presence of various pH2. With increasing pH2, a 5-fold increase was observed in O2 uptake, and CO2 evolution declined such that net CO2 fixation was observed in treatments of 680 ppm H2 or more. At the H2 exposure rate used to pretreat the soil, 60% of the electrons from H2 were passed to O2, and 40% were used to support CO2 fixation. The effect of H2 on the energy and C metabolism of soil may account for the well-known effect of legumes in promoting soil C deposition.  相似文献   

5.
Summary In jejunal brush-border membrane vesicles, an outwardly directed OH gradient (in>out) stimulates DIDS-sensitive, saturable folate (F) uptake (Schron, C.M. 1985.J. Clin. Invest. 76:2030–2033), suggesting carrier-mediated folate: OH exchange (or phenomenologically indistinguishable H+: folate cotransport). In the present study, the precise role of pH in the transport process was elucidated by examining F uptake at varying pH. For pH gradients of identical magnitude, F uptake (0.1 M) was greater at lower (pHint/pHext: 5.5/4.5) compared with higher (6.5/5.5) pH ranges. In the absence of a pH gradient, internal Ftrans stimulated DIDS-sensitive3H-folate uptake only at pH6.0. Since stepwise increments ininternal pH (4.57.5; pHext=4.5) stimulated F uptake, an inhibitory effect of higherinternal pH was excluded. In contrast, with increasing external pH (4.356.5; pHint=7.8), a 50-fold decrement in F uptake was observed (H+ K m =12.8±1.2 M). Hill plots of these data suggest involvement of at least one H+ (OH) at low pH (monovalent F predominates) and at least 2 H+ (OH) at high pH (divalent F–2 predominates). Since an inside-negative electrical potential did not affect F uptake at either pHext 4.55 or 5.8, transport of F and F–2 is electroneutral. Kinetic parameters for F and F–2 were calculated from uptake data at pHext 4.55 and 5.0. Comparison of predictedvs. experimentally determined kinetic parameters at pHext5.8 (K m =1.33vs. 1.70 M;V max=123.8vs. 58.0 pmol/mg prot min) suggest that increasing external pH lowers theV max, but does not affect theK m for carrier-mediated F transport. These data are consistent with similarK i ' s for sulfasalazine (competitive inhibitor) at pHext 5.35 and 5.8 (64.7 and 58.5 M, respectively). In summary, the jejunal F carrier mediates electroneutral transport of mono- and divalent F and is sensitive to external pH with a H+ K m (or OH lC50) corresponding to pH 4.89. External pH effects theV max, but not theK m for carriermediated F uptake suggesting a reaction mechanism involving a ternary complex between the outward-facing conformation of the carrier and the transported ions (F and either OH or H+),rather than competitive binding that is mutually exclusive.  相似文献   

6.
Summary Radiosodium efflux from barnacle muscle fibers is a function of pH e , the threshold pH e for stimulation of Na efflux into HCO 3 -artificial sea water (ASW) being 6.8 and the fixed thresholdpCO2 (in an open CO2 system) being approximately 30 mm Hg. Acidification of ASW containing non-HCO 3 buffer is without effect on the Na efflux. The Na efflux following stimulation by reducing the pH of 10mM HCO 3 -ASW from 7.8 to 6.3 is reduced by 17.3% as the result of microinjecting 100mM EGTA, and increased by 32.6% as the result of microinjecting 0.5M ATP. The Na efflux into K-free HCO 3 -ASW is markedly stimulated by external acidification. Ouabain-poisoned fibers are more responsive to a low pH e than unpoisoned fibers. Applying the 2-14C-DMO technique, it is found that fibers bathed in 10mM HCO 3 -ASW at pH 7.8 have an internal pH of 7.09±0.106 (mean±SD), whereas fibers bathed in 25mM TRIS-ASW at pH 7.8 have a pH i of 7.28±0.112. The relationship between pH i and pH e as external pH is varied by adding H+ is linear. Measurements of the resting membrane potential indicate that external acidification in the presence of HCO 3 as buffer is accompanied by a fall inE m , the threshold pH e being 7.3 both at 24 and 0°C. This sensitivity amounts to 8.2 mV per pH unit (at 24°C) over a wide range of pH e . Membrane resistance following external acidification remains unchanged. Microinjection of the protein inhibitor of Walsh before external acidification fails to stop depolarization from occurring. Cooling to 0°C also fails to abolish depolarization following acidification. Whereas external ouabain and ethacrynic acid reduceE m in the absence or presence of acidification, DPH hyperpolarizes the membrane or arrests depolarization both at 24 and 0°C. This effect of DPH at 0°C is seen in the absence or presence of acidification. It is suggested that depolarization following acidification of a HCO 3 -containing medium is due to activation of a Cl-and/or HCO 3 -pump and that ouabain and ethacrynic acid reducesE m by abolishing uncoupled Na transport.  相似文献   

7.
Summary In jejunal brush-border membrane vesicles, an out-wardly directed OH gradient (in>out) stimulates DIDS-sensitive, saturable folate (F) uptake (Schron, C.M., 1985).J. Clin. Invest. 76:2030–2033), suggesting carrier-mediated folate: OH exchange (or phenomenologically indistiguishable H+: folate cotransport). In the present study, the precise role of pH in the transport process was elucidated by examinin F uptake at varying pH. For pH gradients of identical magnitude, F uptake (0.1 M) was geater at lower (pHint/pHext:5.5/4.5) compared with higher (6.5/5.5) pH ranges. In the absence of a pH gradient, internal Ftrans stimulated DIDS-sensitive3H-folate uptake only at pH6.0. Since setepwise increments ininternal pH (4.57.5; pHext=4.5) stimulated F uptake, an inhibitory effect of higherinternal pH was excluded. In contrast, with increasing external pH(4.356.5; pHint=7.8), a 50-fold decrement in F uptake was observed (H+ K m =12.8±1.2m). Hill plots of these data suggest involvement of at least one H+ (OH) at high pH (divalent F–2 predominates). Since an inside-negative electrical potential did not affect F uptake at either pHext 4.55 or 5.8, transport of F and F–2 is electroneutral. Kinetic parameters for F and F–2 were calculated from uptake data at pHext 4.55 and 5.0. Comparision of predictedvs. experimentally determined kinetic parameters at pHext 5.8 (K m =1.33vs. 1.70 m;V max=12.8vs. 58.0 pmol/mg prot min) suggest that increasing external pH lowers theV max, but does not affect thatK m, for carrier-mediated F transport. These data are consistent with similarK i's for sulfasalazine (competitive inhibitor) at pHext 5.35 and 5.8 (64.7 and 58.5 m, respectively). In summary, the jejunal F carrier mediates electroneutral transport of mono- and divalen F and is sensitive to extermal pH with a H+ K m (or OH IC50) corresponding to pH 4.89. External pH affects theV max, but not theK m for carriermediated F uptake suggesting a reaction mechanism involving a ternary complex between the outward-facing conformation of the carrier and the transported ions (F and either OH or H+) rather than competitive binding that is mutually exclusive.  相似文献   

8.
Methanosarcina barkeri strain 227 produced ethane during growth on H2/CO2 when ethanol was added to the medium in concentrations of 89–974 mM; ethane production varied from 14 to 38 nmoles per tube (20 ml gas phase, 5.7 ml liquid) with increasing ethanol concentrations. Cells grown to mid-logarithmic phase (A600 0.46, protein = 64 g/ml) on H2/CO2, thoroughly flushed with H2/CO2, then exposed to ethanol, produced maximal ethane levels (at 585 and 974 mM ethanol) of about 215 nmoles per tube, with an ethane/methane ratio of 1×10-3. Mid-logarithmic-phase cultures of Methanosarcina barkeri strain Fusaro also produced ethane (up to 20 nmoles per tube) when exposed to ethanol. Cultures of strain 227 growing on methanol in the absence of H2 produced 6 nmoles per tube of ethane when supplemented with ethanol whereas those lacking ethanol but containing H2 and/or methanol produced 1.6 nmoles per tube. Cultures of Methanococcus deltae strains LH and RC, Methanospirillum hungatei or Methanobacterium thermoautotrophicum produced 5 nmoles ethane per tube when grown in medium containing ethanol. Ethanol concentrations of 177–886 mM were inhibitory to growth of all methanogens examined. Production of ethane by Methanosarcina was inhibited by >62 mM methanol, and both methanogenic inhibitors tested, CCl4 and Br–CH2–CH2–SO inf3 sup- , inhibited ethane and methane production concurrently. The data suggest that ethanol is converted to ethane by Methanosarcina species using the terminal portion of the methanol-to-methane pathway.  相似文献   

9.
An obligately anaerobic thermophilic sporeforming sulfate-reducing bacterium, named strain CAMZ, was isolated from a benzoate enrichment from a 58°C thermophilic anaerobic bioreactor. The cells of strain CAMZ were 0.7 m by 2–5 m rods with pointed ends, forming single cells or pairs. Spores were central, spherical, and caused swelling of the cells. The Gram stain was negative. Electron donors used included lactate, pyruvate, acetate and other short chain fatty acids, short chain alcohols, alanine, and H2/CO2. Lactate and pyruvate were oxidized completely to CO2 with sulfate as electron acceptor. Sulfate was required for growth on H2/CO2, and both acetate and sulfide were produced from H2/CO2-sulfate. Sulfate, thiosulfate, or elemental sulfur served as electron acceptors with lactate as the donor while sulfite, nitrate, nitrite, betaine, or a hydrogenotrophic methanogen did not. The optimum temperature for growth of strain CAMZ was 55–60°C and the optimum pH value was 6.5. The specific activities of carbon monoxide dehydrogenase of cells of strain CAMZ grown on lactate, H2/CO2, or acetate with sulfate were 7.2, 18.1, and 30.8 mol methyl viologen reduced min–1 [mg protein]–1, respectively, indicating the presence of the CO/Acetyl-CoA pathway in this organism. The mol%-G+C of strain CAMZ's DNA was 49.7. The new species name Desulfotomaculum thermoacetoxidans is proposed for strain CAMZ.  相似文献   

10.
Dry weight and Relative Growth Rate of Lemna gibba were significantly increased by CO2 enrichment up to 6000 l CO2 l–1. This high CO2 optimum for growth is probably due to the presence of nonfunctional stomata. The response to high CO2 was less or absent following four days growth in 2% O2. The Leaf Area Ratio decreased in response to CO2 enrichment as a result of an increase in dry weight per frond. Photosynthetic rate was increased by CO2 enrichment up to 1500 l CO2 l–1 during measurement, showing only small increases with further CO2 enrichment up to 5000 l CO2 l–1 at a photon flux density of 210 mol m–2 s–1 and small decreases at 2000 mol m–1 s–1. The actual rate of photosynthesis of those plants cultivated at high CO2 levels, however, was less than the air grown plants. The response of photosynthesis to O2 indicated that the enhancement of growth and photosynthesis by CO2 enrichment was a result of decreased photorespiration. Plants cultivated in low O2 produced abnormal morphological features and after a short time showed a reduction in growth.  相似文献   

11.
Cell suspensions of H2/CO2-grown Sporomusa termitida catalyzed an H2-supported synthesis of acetate from CO2 at rates of about 1 mol acetate x h-1 x mg protein-1. Cells pre-grown on methanol, mannitol, lactate, or glycine also displayed H2-supported acetogenesis from CO2, although at rates 5–85% that of H2/CO2-grown cells. With methanol-grown cell suspensions: the presence of methanol greatly stimulated the rate of H2-supported conversion of 14CO2 to 14C-acetate (which became labeled mainly in the COOH-group); and like-wise the presence of H2 stimulated the conversion of 14CH3OH+CO2 to 14C-acetate (which became labeled mainlyan the CH3-group). Analogous stimulatory effects were observed for cell suspensions pre-grown on methanol + CO2+H2. Furthermore, when H2 (+CO2) was included as a growth substrate with either methanol or lactate: both substrates were used simultaneously; there was no diauxie in the growth of cells or in acetate production; and the molar growth yield of S. termitida was close to that predicted from summation of the yields observed when grown with each substrate alone. These data indicated that S. termitida can grow by mixotrophy, i.e. by the simultaneous use of H2/CO2 and organic compounds for energy. Results are discussed in light of the ability of H2/CO2 acetogens to outprocess methanogens in H2 consumption in the hindgut fermentation of wood-feeding termites.  相似文献   

12.
Summary The method of the measurement of the nonelectrogenic fluxes of hydrogen (or hydroxyl) ions (J H) based on the local proton gradients formation in the unstirred layers near a bilayer lipid membrane (BLM) is applied for recording the nonelectrogenic anion/OH exchange on BLM induced by tributyltin (TBT) and a novel carrier (Hager, A., Moser, I., & Berthold, W. 1987.Z. Naturforsch.,42C1116–1120), triethyllead (TEL). This method has been used previously for measuring the cation fluxes through BLM. TBT and TEL are shown to be equally efficient in the induction of Cl/OH exchange.J H induced by TBT is constant at 4J H decreases at pH<4 and pH>7. Both ionophores have a transport sequence: I> Br>Cl>F. The quatitative measurements reveal that TEL better discriminates these four anions than TBT. It is concluded that this method may prove helpful in a search and study of anion/OH-exchangers isolated from natural membranes.  相似文献   

13.
Yields based on carbon are usually reported in prebiotic experiments, while energy yields (moles cal–1) are more useful in estimating the yields of products that would have been obtained from the primitive atmosphere of the earth. Energy yields for the synthesis of HCN and H2CO from a spark discharge were determined for various mixtures of CH4, CO, CO2, H2, H2O, N2 and NH3. The maximum yields of HCN and H2CO from CH4, CO, and CO2 as carbon sources are about 4×10–8 moles cal–1.  相似文献   

14.
The mineralization of organic carbon to CH4 and CO2 inSphagnum-derived peat from Big Run Bog, West Virginia, was measured at 4 times in the year (February, May, September, and November) using anaerobic, peat-slurry incubations. Rates of both CH4 production and CO2 production changed seasonally in surface peat (0–25 cm depth), but were the same on each collection date in deep peat (30–45 cm depth). Methane production in surface peat ranged from 0.2 to 18.8 mol mol(C)–1 hr–1 (or 0.07 to 10.4 g(CH4) g–1 hr–1) between the February and September collections, respectively, and was approximately 1 mol mol(C)–1 hr–1 in deep peat. Carbon dioxide production in surface peat ranged from 3.2 to 20 mol mol(C)–1 hr–1 (or 4.8 to 30.3 g(CO2) g–1 hr–1) between the February and September collections, respectively, and was about 4 mol mol(C)–1 hr–1 in deep peat. In surface peat, temperature the master variable controlling the seasonal pattern in CO2 production, but the rate of CH4 production still had the lowest values in the February collection even when the peat was incubated at 19°C. The addition of glucose, acetate, and H2 to the peat-slurry did not stimulate CH4 production in surface peat, indicating that CH4 production in the winter was limited by factors other than glucose degradation products. The low rate of carbon mineralization in deep peat was due, in part, to poor chemical quality of the peat, because adding glucose and hydrogen directly stimulated CH4 production, and CO2 production to a lesser extent. Acetate was utilized in the peat by methanogens, but became a toxin at low pH values. The addition of SO4 2– to the peat-slurry inhibited CH4 production in surface peat, as expected, but surprisingly increased carbon mineralization through CH4 production in deep peat. Carbon mineralization under anaerobic conditions is of sufficient magnitude to have a major influence on peat accumulation and helps to explain the thin (< 2 m deep), old (> 13,000 yr) peat deposit found in Big Run Bog.  相似文献   

15.
Accumulation of formate to millimolar levels was observed during the growth of Methanobacterium formicicum species on H2–CO2. Hydrogen was also produced during formate metabolism by M. formicicum. The amount of formate accumulated in the medium or the amount H2 released in gas phase was influenced by the bicarbonate concentration. The formate hydrogenlyase system was constitutive but regulated by formate. When methanogenesis was inhibited by addition of 2-bromoethane sulfonate, M. formicicum synthesized formate from H2 plus HCO inf3 sup- or produced H2 from formate to a steady-state level at which point the Gibbs free energy (G) available for formate synthesis or H2 production was approximately -2 to -3 kJ/reaction. Formate conversion to methane was inhibited in the presence of high H2 pressure. The relative rates of conversion of formate and H2 were apparently controlled by the G available for formate synthesis, hydrogen production, methane production from formate and methane production from H2. Results from 14C-tracer tests indicated that a rapid isotopic exchange between HCOO- and HCO inf3 sup- occurred during the growth of M. formicicum on H2–CO2. Data from metabolism of 14C-labelled formate to methane suggested that formate was initially split to H2 and HCO inf3 sup- and then subsequently converted to methane. When molybdate was replaced with tungstate in the growth media, the growth of M. formicicum strain MF on H2–CO2 was inhibited although production of methane was not Formate synthesis from H2 was also inhibited.  相似文献   

16.
The electrochemical gradient of protons, , was estimated in the obligatory aerobic yeastRhodotorula glutinis in the pH0 range from 3 to 8.5. The membrane potential, , was measured by steady-state distribution of the hydrophobic ions, tetraphenylphosphonium (TPP+) for negative above pH0 4.5, and thiocyanate (SCN) for positive below pH0 4.5. The chemical gradient of H+ was determined by measuring the chemical shift of intracellular Pi by31P-NMR at given pH0 values. The values of pHi increased almost linearly from 7.3 at pH0 3 to 7.8 at pH0 8.5. In the physiological pH0 range from 3.5 to 6, was fairly constant at values between 17–18 KJ mol–1, gradually decreasing at pH0 above 6. In deenergized cells, the intracellular pHi decreased to values as low as 6, regardless of whether the cell suspension was buffered at pH0 4.5 or 7.5. There was no membrane potential detectable in deenergized cells.  相似文献   

17.
The influence of cytosolic pH (pHi) in controlling K+-channel activity and its interaction with cytosolic-free Ca2+ concentration ([Ca2+]i) was examined in stomatal guard cells ofVicia faba L. Intact guard cells were impaled with multibarrelled microelectrodes and K+-channel currents were recorded under voltage clamp while pHi or [Ca2+]i was monitored concurrently by fluorescence ratio photometry using the fluorescent dyes 2,7-bis (2-carboxyethyl)-5(6)-carboxyfluorescein (BCECF) and Fura-2. In 10 mM external K+ concentration, current through inward-rectifying K+ channels (IK,in) was evoked on stepping the membrane from a holding potential of –100 mV to voltages from –120 to –250 mV. Challenge with 0.3-30 mM Na+-butyrate and Na+-acetate outside imposed acid loads, lowering pHi from a mean resting value of 7.64 ± 0.03 (n = 25) to values from 7.5 to 6.7. The effect on pHi was independent of the weak acid used, and indicated a H+-buffering capacity which rose from 90 mM H+/pH unit near 7.5 to 160 mM H+/pH unit near pHi 7.0. With acid-going pHi, (IK,in) was promoted in scalar fashion, the current increasing in magnitude with the acid load, but without significant effect on the current relaxation kinetics at voltages negative of –150 mV or the voltage-dependence for channel gating. Washout of the weak acid was followed by transient rise in pHi lasting 3–5 min and was accompanied by a reduction in (IK,in) before recovery of the initial resting pHi and current amplitude. The pHi-sensitivity of the current was consistent with a single, titratable site for H+ binding with a pKa near 6.3. Acid pHi loads also affected current through the outward-rectifying K+ channels (IK,out) in a manner antiparallel to (IK,in) The effect on IK, out was also scalar, but showed an apparent pKa of 7.4 and was best accommodated by a cooperative binding of two H+. Parallel measurements showed that Na+-butyrate loads were generally without significant effect on [Ca2+]i, except when pHi was reduced to 7.0 and below. Extreme acid loads evoked reversible increases in [Ca2+]i in roughly half the cells measured, although the effect was generally delayed with respect to the time course of pHi changes and K+-channel responses. The action on [Ca2+]i coincided with a greater variability in (IK,in) stimulation evident at pHi values around 7.0 and below, and with negative displacements in the voltage-dependence of (IK,in) gating. These results distinguish the actions of pHi and [Ca2+]i in modulating (IK,in) they delimit the effect of pHi to changes in current amplitude without influence on the voltage-dependence of channel gating; and they support a role for pHi as a second messenger capable of acting in parallel with, but independent of [Ca2+]i in controlling the K+ channels.Abbreviations BCECF 2,7-bis (2-carboxyethyl)-5(6)-carboxy fluorescein - [Ca2+]i cytosolic free Ca2+ concentration - gK ensemble (steady-state) K+-channel conductance - IK,out, IK,in outward-, inward-rectifying K+ channel (current) - IN current-voltage (relation) - Mes 2-(N-morpholinolethanesulfonic acid - pHi cytosolic pH - V membrane potential  相似文献   

18.
Summary Changes in extracellular pH (pHo) in red cell suspensions were monitored in a stopped-flow rapid reaction apparatus under conditions wheredpHo/dt was determined by the rate of HCO 3 /Cl exchange across the membrane. Experiments were performed at 5°C<T<40°C using either untreated cells or cells exposed to 0.11mm SITS (4-acetamido-4-isothiocyanostilbene-2,2-disulfonic acid). Although SITS exposure reduced the rate of exchange by 90%, both untreated and SITS-treated cells are similarly affected by changes in pH0 and temperature. The rate of HCO 3 /Cl exchange exhibits a minimum at about pHo 5 and a maximum at about pH0 7.4 at all temperatures. A transition temperature of 17°C was observed in the Arrhenius relationship for all pH0. The activation energies (E a) in kcal/mol are 19.6 below and 11.7 above 17°C for 50<8. These findings, similar to those reported for Cl self-exchange, suggest that: (i) a change in the rate-limiting step for HCO 3 /Cl exchange occurs at 17°C, possibly due to an altered interaction between the transport pathway and membrane lipids; (ii) the carrier system can be titrated by either H+ or SITS from the outside of the membrane, but the untitrated sites continue to transport normally; (iii) the pH0 dependence of the rate of exchange is consistent with the titratable carrier having its most alkaline pK in the range expected for amino groups; and (iv) below pH0 5, the nature of the exchange is markedly altered.  相似文献   

19.
Photoautotrophic micropropagation of Russet Burbank Potato   总被引:2,自引:0,他引:2  
The photoautotrophic micropropagation of potato cv. Russet Burbank was investigated. Single node microcuttings were grown for four weeks on Murashige and Skoog (MS) medium with or without sucrose (30 g l–1) in the growth room at 21/19 °C day/night temperature, with 16-h photoperiod at 150 mol m–2 s–1, with or without supplemental CO2 at 1500 l l–1. A 20% increase in the number of nodes per stem (from 7.5 to 9.4) and a 50% increase in stem dry weight were observed in cultures grown on media with sucrose and in CO2 enriched atmosphere comparing to the conventionally micropropagated cultures or the cultures grown photoautotrophically on media without sucrose but in air supplemented with 1500 l l–1CO2. Stems of these cultures (from media with sucrose in CO2 enriched air) almost doubled in length the stems of cultures from the other two treatments. No significant differences were observed between Control (MS medium supplemented with sucrose, 30 g l–1) and photoautotrophic cultures coming from MS medium with no sucrose grown under 1500 l l–1 of CO2. Photoautotrophic cultures produced stems averaging 43.3 mm, with 7 nodes and weighing 9.2 mg (dry weight), similar to conventionally grown in vitro cultures (47.9 mm with 7.5 nodes, 9.7 mg dry weight). Growers may consider photoautotrophic culturing of potato in areas where the high sterility levels are difficult to maintain. Supplementing air in the growth room with 1500 l l–1 of CO2 could be beneficial for potato plantlet production even on media containing sucrose since it significantly improved quality, size and biomass of produced plantlets, speeding up the multiplication.  相似文献   

20.
Summary Quantitative analysis has been made of the reactions underlying the Hansson histochemical method for carbonic anhydrase, with a view toward resolving controversies that have arisen regarding its application and specificity.The basic event is the loss of CO2 from the surface of solutions containing HCO 3 , PO 4 2– and cobalt at pH 6–8. Displacement of the equilibria H2CO3 CO2 to the right elevates the pH, and at 6.8 a cobalt precipitate is formed. When tissue containing carbonic anhydrase is floated on the surface, the loss of CO2 and elevation of pH is accelerated at the enzyme site, leading to ncreased cobalt deposits. These are converted to cobalt sulphide for visualization.Study of the changes of pH and CO2 equilibria during the reaction point strongly to the fact that enzymic activity is being measured by the cobalt localization. This activity is reduced or abolished by appropriate concentrations of acetazolamide (or other sulphonamide inhibitors of carbonic anhydrase) and the powerful inorganic inhibitor, cyanate (CNO) ion.  相似文献   

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