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1.
Local illumination of the characean internode with a 30-s pulse of white light was found to induce the delayed transient increase of modulated chlorophyll fluorescence in shaded cell parts, provided the analyzed region is located downstream in the cytoplasmic flow at millimeter distances from the light spot. The fluorescence response to photostimulation of a remote cell region indicates that the metabolites produced by source chloroplasts in an illuminated region are carried downstream with the cytoplasmic flow, thus ensuring long-distance communications between anchored plastids in giant internodal cells. The properties of individual stages of metabolite signaling are not yet well known. We show here that the export of assimilates and/or reducing equivalents from the source chloroplasts into the flowing cytoplasm is largely insensitive to the direction of plasma-membrane H+ flows, whereas the events in sink regions where these metabolites are delivered to the acceptor chloroplasts under dim light are controlled by H+ fluxes across the plasma membrane. The fluorescence response to local illumination of remote cell regions was best pronounced under weak background light and was also observed in a modified form within 1–2 min after the transfer of cell to darkness. The fluorescence transients in darkened cells were suppressed by antimycin A, an inhibitor of electron transfer from ferredoxin to plastoquinone, whereas the fluorescence response under background light was insensitive to this inhibitor. We conclude that the accumulation of reduced metabolites in the stroma leads to the reduction of photosystem II primary quinone acceptor (QA) via two separate (photochemical and non-photochemical) pathways. 相似文献
2.
The role of cytoplasmic streaming in pattern formation at the plasma membrane and chloroplast layer was examined with Chara corallina Klein ex Willd. cells exposed to nonuniform illumination. Our hypothesis was that the exchange of ions and metabolites between
the chloroplasts and the cytoplasm in the illuminated cell area alters the composition of the cytosol while the flow of modified
cytoplasm induces asymmetrical changes in the plasmalemmal transport and fluorescence of chloroplasts in the adjacent shaded
areas. The hypothesis was tested by measuring the H+-transporting activity of plasmalemma and non-photochemical quenching (NPQ) in shaded areas of Chara cells at distances of 1–5 mm on either side of the illuminated region (white light, 1000 μmol/(m2 s), beam width 2 mm). When measured at equal distances on opposite sides from the illuminated region, both pH and NPQ changes
differed considerably depending on the direction of cytoplasmic movement at the light-shade boundary. In the region where
the cytoplasm flowed out of irradiated area, the formation of alkaline zone (the plasma membrane domain with a high H+-conductance) and NPQ in chloroplasts was observed. In the vicinity of light-shade boundary where the flow was directed from
the shade to the illuminated area, neither alkaline zone nor NPQ were formed. The results demonstrate the significance of
cyclosis in the transfer of physiologically active intermediate that affects the membrane transport, the functional activity
of chloroplasts, and the pattern formation in the plant cell. 相似文献
3.
A ouabain sensitive inward current occurs in Xenopus oocytes in Na+ and K+ -free solutions. Several laboratories have investigated the properties of this current and suggested that acidic extracellular pH (pHo) produces a conducting pathway through the Na+/K+ pump that is permeable to H+ and blocked by [Na+]o. An alternative suggestion is that the current is mediated by an electrogenic H+-ATPase. Here we investigate the effect of pHo and [Na+]o on both transient and steady-state ouabain-sensitive current. At alkaline or neutral pHo the relaxation rate of pre-steady-state current is an exponential function of voltage. Its U-shaped voltage dependence becomes apparent at acidic pHo, as predicted by a model in which protonation of the Na+/K+ pump reduces the energy barrier between the internal solution and the Na+ occluded state. The model also predicts that acidic pHo increases steady-state current leak through the pump. The apparent pK of the titratable group(s) is 6, suggesting that histidine is involved in induction of the conductance pathway. 22Na efflux experiments in squid giant axon and current measurements in oocytes at acidic pHo suggest that both Na+ and H+ are permeant. The acid-induced inward current is reduced by high [Na+]o, consistent with block by Na+. A least squares analysis predicts that H+ is four orders of magnitude more permeant than Na+, and that block occurs when 3 Na+ ions occupy a low affinity binding site (K
0.5=130±30 mM) with a dielectric coefficient of 0.23±0.03. These data support the conclusion that the ouabain-sensitive conducting pathway is a result of passive leak of both Na+ and H+ through the Na+/K+ pump. 相似文献
4.
T. I. Ivanova A. O. Sherstobitov G. P. Gusev 《Journal of Evolutionary Biochemistry and Physiology》2007,43(6):557-563
To activate Na+/H+ exchange, intracellular pH (pHi) of erythrocytes of the river lamprey Lampetra fluviatilis were changed from 6 and 8 using nigericin. The Na+/H+ exchanger activity was estimated from the values of amiloride-sensitive components of Na+ (22Na) inflow or of H+ outflow from erythrocytes. Kinetic parameters of the carrier functioning were determined by using Hill equation. Dependence of Na+ and H+ transport on pHi value is described by hyperbolic function with the Hill coefficient value (n) close to 1. Maximal rate of ion transport was within the limits of 9–10 mmol/l cells/min, and the H+ concentration producing the exchanger 50% activation amounted to 0.6–1.0 μM. Stimulation of H+ outcome from acidified erythrocytes (pHi 5.9) with increase of H+ concentration in the incubation medium is described by Hill equation with n value of 1.6. Concentration Na+ for the semimaximal stimulation of H+ outcome amounted to 10 mM. The obtained results indicate the presence in lamprey erythrocytes of only binding site for H+ from the cytoplasm side and the presence of positive cooperativity in Na+-binding from the extracellular side of the Na+/H+ exchanger. Na+ efflux from cells in the Na+-free medium did not change at a 10-fold increase of H+ concentration in the incubation medium. The presented data indicate differences of kinetic properties of the lamprey erythrocyte Na+/H+ exchanger and of this carrier isoforms in mammalian cells. In intact erythrocytes the dependence of the amiloride-sensitive Na+ inflow on its concentration in the medium is described by Hill equitation with n 1.6. The Na+ concentration producing the 50% transport activation amounted to 39 mM and was essentially higher as compared with that in acidified erythrocytes. These data confirm conception of the presence of two amiloride-sensitive pathways of Na+ transport in lamprey erythrocytes. 相似文献
5.
GYENES M.; ANDRIANOV V. K.; BULYCHEV A. A.; KURELLA G. A. 《Journal of experimental botany》1978,29(5):1185-1195
The effects of light on the pH in the vacuole and the electricpotential difference across the plasmalemma and the tonoplastof Nitellopsis obtusa were investigated by means of conventionaland H+-specific glass or antimony microelectrodes. Illuminationis found to bring about a decrease in the pH of the vacuolarsap by 0.10.5 units concomitant with a depolarizationof the cell. The light-induced changes of the potential differenceand the vacuolar pH depend in different ways on the pH of theexternal medium (pHo). At pHo 9.0 cells exhibit great light-inducedpotential changes (up to 100 mV), but only small pH changesof the vacuolar sap. At neutral or slightly acidic pHo valuesthe amplitude of the light-induced pH changes in the vacuoleincreases up to 0.30.5 pH units, but the amplitudes ofthe potential changes at the plasmalemma are relatively small.At pHo 9.0 a transient acidification of the medium is observedupon illumination whereas at lower pH values light-induced alkalinizationwas only seen. Transfer of the cells from pHo 9.0 to pHo 7.5results in a cell hyperpolarization by 6080 mV and adecrease of the vacuolar pH by 0.40.5 units under lightconditions but has no significant effect on the potential andthe vacuolar pH in the darkness. It is proposed that mechanismsof active H+ extrusion from the cytoplasm are located both inthe plasmalemma and the tonoplast. The observed acidificationin the vacuole appears to be determined by a light-induced increaseof the concentration of H+ in the cytoplasm. The H+ conductionof the plasmalemma seems to increase on illumination. The patternof the light-induced H+ fluxes across the tonoplast and theplasmalemma depends crucially on the extent of the light-inducedchanges in the H+ conductance and on the electrochemical gradientfor H+ at the plasmalemma. 相似文献
6.
Summary We have investigated the kinetic properties of the human red blood cell Na+/H+ exchanger to provide a tool to study the role of genetic, hormonal and environmental factors in its expression as well as its functional properties in several clinical conditions. The present study reports its stoichiometry and the kinetic effects of internal H+ (H
i
) and external Na+ (Na
o
) in red blood cells of normal subjects.Red blood cells with different cell Na+ (Na
i
) and pH (pH
i
) were prepared by nystatin and DIDS treatment of acid-loaded cells. Unidirectional and net Na+ influx were measured by varying pH
i
(from 5.7 to 7.4), external pH (pH
o
), Na
i
and Na
o
and by incubating the cells in media containing ouabain, bumetanide and methazolamide. Net Na+ influx (Na
i
<2.0 mmol/liter cell, Na
o
= 150mm) increased sigmoidally (Hill coefficient 2.5) when pH
i
fell below 7.0 and the external pH
o
was 8.0, but increased linearly at pH
o
6.0. The net Na+ influx driven by an outward H+ gradient was estimated from the difference of Na+ influx at the two pH
o
levels (pH
o
8 and pH
o
6). The H+-driven Na+ influx reached saturation between pH
i
5.9 and 6.1. TheV
max had a wide interindividual variation (6 to 63 mmol/liter cell · hr, 31.0±3, mean±sem,n=20). TheK
m
for H
i
to activate H+-driven Na+ influx was 347±30nm (n=7). Amiloride (1mm) or DMA (20 m) partially (59±10%) inhibited red cell Na+/H+ exchange. The stoichiometric ratio between H+-driven Na+ influx and Na+-driven H+ efflux was 11. The dependence of Na+ influx from Na
o
was studied at pH
i
6.0, and Na
i
lower than 2 mmol/liter cell at pH
o
6.0 and 8.0. The meanK
m
for Na
o
of the H+-gradient-driven Na+ influx was 55±7mm.An increase in Na
i
from 2 to 20 mmol/liter cell did not change significantly H+-driven net Na+ influx as estimated from the difference between unidirectional22Na influx and efflux. Na+/Na+ exchange was negligible in acid-loaded, DIDS-treated cells. Na+ and H+ efflux from acid-loaded cells were inhibited by amiloride analogs in the absence of external Na+ indicating that they may represent nonspecific effects of these compounds and/or uncoupled transport modes of the Na+/H+ exchanger.It is concluded that human red cell Na+/H+ exchange performs 11 exchange of external Na+ for internal protons, which is partially amiloride sensitive. Its kinetic dependence from internal H+ and external Na+ is similar to other cells, but it displays a larger variability in theV
max between individuals. 相似文献
7.
Cytoplasmic streaming occurs in most plant cells and is vitally important for large cells as a means of long-distance intracellular transport of metabolites and messengers. In internodal cells of characean algae, cyclosis participates in formation of light-dependent patterns of surface pH and photosynthetic activity, but lateral transport of regulatory metabolites has not been visualized yet. Hydrogen peroxide, being a signaling molecule and a stress factor, is known to accumulate under excessive irradiance. This study was aimed to examine whether H2O2 produced in chloroplasts under high light conditions is released into streaming fluid and transported downstream by cytoplasmic flow. To this end, internodes of Chara corallina were loaded with the fluorogenic probe dihydrodichlorofluorescein diacetate and illuminated locally by a narrow light beam through a thin optic fiber. Fluorescence of dihydrodichlorofluorescein (DCF), produced upon oxidation of the probe by H2O2, was measured within and around the illuminated cell region. In cells exhibiting active streaming, H2O2 first accumulated in the illuminated region and then entered into the streaming cytoplasm, giving rise to the expansion of DCF fluorescence downstream of the illuminated area. Inhibition of cyclosis by cytochalasin B prevented the spreading of DCF fluorescence along the internode. The results suggest that H2O2 released from chloroplasts under high light is transported along the cell with the cytoplasmic flow. It is proposed that the shift of cytoplasmic redox poise and light-induced elevation of cytoplasmic pH facilitate the opening of H+/OH?-permeable channels in the plasma membrane. 相似文献
8.
How focal seizures initiate and evolve in human neocortex remains a fundamental problem in neuroscience. Here, we use biophysical neuronal network models of neocortical patches to study how the interaction between inhibition and extracellular potassium ([K +] o ) dynamics may contribute to different types of focal seizures. Three main types of propagated focal seizures observed in recent intracortical microelectrode recordings in humans were modelled: seizures characterized by sustained (~30?60 Hz) gamma local field potential (LFP) oscillations; seizures where the onset in the propagated site consisted of LFP spikes that later evolved into rhythmic (~2?3 Hz) spike-wave complexes (SWCs); and seizures where a brief stage of low-amplitude fast-oscillation (~10?20 Hz) LFPs preceded the SWC activity. Our findings are fourfold: (1) The interaction between elevated [K +] o (due to abnormal potassium buffering by glial cells) and the strength of synaptic inhibition plays a predominant role in shaping these three types of seizures. (2) Strengthening of inhibition leads to the onset of sustained narrowband gamma seizures. (3) Transition into SWC seizures is obtained either by the weakening of inhibitory synapses, or by a transient strengthening followed by an inhibitory breakdown (e.g. GABA depletion). This reduction or breakdown of inhibition among fast-spiking (FS) inhibitory interneurons increases their spiking activity and leads them eventually into depolarization block. Ictal spike-wave discharges in the model are then sustained solely by pyramidal neurons. (4) FS cell dynamics are also critical for seizures where the evolution into SWC activity is preceded by low-amplitude fast oscillations. Different levels of elevated [K +] o were important for transitions into and maintenance of sustained gamma oscillations and SWC discharges. Overall, our modelling study predicts that the interaction between inhibitory interneurons and [K +] o glial buffering under abnormal conditions may explain different types of ictal transitions and dynamics during propagated seizures in human focal epilepsy. 相似文献
9.
Intracellular transport assisted by rotatory cytoplasmic movement in characean green algae exerts regulatory influence on plasmalemmal ion channels and photosynthetic activity of chloroplasts. In internodal cells of Chara corallina Klein ex Willd., the photoinduced signal transmitted with the flow of streaming cytoplasm for a distance of 1–3 mm from the site of its emergence was found to release or enhance non-photochemical quenching of chlorophyll fluorescence, depending on the intensity of background illumination in the analyzed area. Under dim background irradiance (10–30 μmol quanta/(m2s)), the distant signal transferred from brightly illuminated 0.4-mm-wide area elicited a transient increase in maximal (F′m) and actual (F) fluorescence. However, at higher background irradiances, the arrival of the same signal resulted in strong quenching of F′m and in transitory changes of F. The transformation of “low light response” to F′m changes of opposite polarity occurred at some threshold irradiance. Hence, even slight variations in irradiance at the chloroplast layer, attributed to structural features of characean internodes, might promote formation of uneven photosynthetic profile under the influence of signals transmitted along the cell with the cytoplasmic flow. Analysis of chloroplast fluorescence in situ as a function of pH in experiments with intracellular perfusion indicated that the initial response to a distant light stimulus is caused by the transient increase in cytoplasmic pH in the area of fluorescence measurements. 相似文献
10.
Relationship between Acid Tolerance, Cytoplasmic pH, and ATP and H+-ATPase Levels in Chemostat Cultures of Lactococcus lactis
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The acid tolerance response (ATR) of chemostat cultures of Lactococcus lactis subsp. cremoris NCDO 712 was dependent on the dilution rate and on the extracellular pH (pHo). A decrease in either the dilution rate or the pHo led to a decrease in the cytoplasmic pH (pHi) of the cells, and similar levels of acid tolerance were observed at any specific pHi irrespective of whether the pHi resulted from manipulation of the growth rate, manipulation of the pHo, or both. Acid tolerance was also induced by sudden additions of acid to chemostat cultures growing at a pHo of 7.0, and this induction was completely inhibited by chloramphenicol. The end products of glucose fermentation depended on the growth rate and the environmental pHo of the cultures, but neither the spectrum of end products nor the total rate of acid production correlated with a specific pHi. The rate of ATP formation was not correlated with pHi, but a good correlation between the cellular level of H+-ATPase and pHi was observed. Moreover, an inverse correlation between the cytoplasmic levels of ATP and pHi was established. Each pHi below 6.6 was characterized by unique levels of ATR, H+-ATPase, and ATP. High levels of H+-ATPase also coincided with high levels of acid tolerance of cells in batch cultures induced with sublethal levels of acid. We concluded that H+-ATPase is one of the ATR proteins induced by acid pHi through growth at an acid pHo or a slow growth rate. 相似文献
11.
Cytoplasmic streaming in plant cells is an effective means of intracellular transport. The cycling of ions and metabolites
between the cytosol and chloroplasts in illuminated cell regions may alter the cytoplasm composition, while directional flow
of this modified cytoplasm may affect the plasma membrane and chloroplast activities in cell regions residing downstream of
the illumination area. The impact of local illumination is predicted to be asymmetric because the cell regions located downstream
and upstream in the cytoplasmic flow with respect to illumination area would be exposed to flowing cytoplasm whose solute
composition was influenced by photosynthetic or dark metabolism. This hypothesis was checked by measuring H+-transporting activity of plasmalemma and chlorophyll fluorescence of chloroplasts in shaded regions of Chara corallina internodal cells near opposite borders of illuminated region (white light, beam width 2 mm). Both the apoplastic pH and chlorophyll
fluorescence, recorded in shade regions at equal distances from illuminated area, exhibited asymmetric light-on responses
depending on orientation of cytoplasmic streaming at the light–shade boundary. In the region where the cytoplasm flowed from
illuminated area to the measurement area, the alkaline zone (a zone with high plasma membrane conductance) was formed within
4-min illumination, whereas no alkaline zone was observed in the area where cytoplasm approached the boundary from darkened
regions. The results emphasize significance of cyclosis in lateral distribution of a functionally active intermediate capable
of affecting the membrane transport across the plasmalemma, the functional activity of chloroplasts, and pattern formation
in the plant cell. 相似文献
12.
Summary Recently we proposed that cytoplasmic acidification of low K+ (LK) sheep erythrocytes may stimulate ouabain-resistant Cl–-dependent K+ flux (K+Cl– cotransport), also known to be activated by cell swelling, treatment with N-ethylmaleimide (NEM), or removal of cellular bivalent cations. Here we studied the dependence of K+ transport on intracellular and extracellular pH (pH
i
, pH
o
) varied either simultaneously or independently using the Cl–/HCO
3
–
exchange inhibitor 4,4, diisothiocyanatostilbene-3,2-disulfonic acid (DIDS). In both control and NEM-treated LK cells volumes were kept near normal by varying extracellular sucrose. Using DIDS as an effective pH clamp, both K+ efflux and influx of Rb+ used as K+ congener were strongly activated at acid pH
i
and alkaline pH
o
. A small stimulation of K+ (Rb+) flux was also seen at acid pH
i
in the absence of DIDS, i.e., when pH
i
pH
o
. Anti-L
l
serum, known to inhibit K+Cl– cotransport, prevented the pH
i
-stimulated K+ (Rb+) fluxes. Subsequent to NEM treatment at pH 6, K+ (Rb+) fluxes were activated only by raising pH, and thus were similar to the pH activation profile of K+ (Rb+) fluxes in DIDS-treated cells with pH
o
varied at constant physiologic pH
i
. Anti-L
l
, which inhibited NEM-stimulated K+ (Rb+) fluxes, failed to do so in NEM-plus DIDS-treated cells. Thus, NEM treatment interferes with the internal but not with the external pH-sensitive site. 相似文献
13.
Summary H+-coupled transport in plant and fungal cells is relatively insensitive to external pH (pH
o
). H+-coupled Cl– transport at the plasma membrane ofChara corallina was studied to explore the phenomena responsible for this insensitivity. Raising pH
o
from a control value of 7.5 to 9.0 results in a modest (2.5-fold) decline inJ
max and increase inK
m
. Further increase in pH
o
results in a selective increase inJ
max, in accordance with predictions from a reaction kinetic model of the transport system (Sanders, D., Hansen, U.-P., 1981.J. Membrane Biol.
58:139–153). Increase in cytosolic Cl– concentration ([Cl–]
c
) also results in a selective decrease inJ
max at pH
o
=7.5.Quantitative kinetic modeling of the results is not possible if it is assumed that the sole effect of pH
o
isvia mass action on the binding of external H+ to a transport site. If, instead, the dependence of cytosolic pH (pH
c
) on pH
o
(Smith, F.A., 1984,J. Exp. Bot.
35:1525–1536) is taken into account along with the dependence of Cl– influx on pH
c
(Sanders, D., 1980,J. Membrane Biol.
53:129–141), then the observed modest changes in Michaelis parameters can be accommodated by a reaction kinetic model. The quantitative parameters of the model yield respective pK
a
s of the internal and external H+-binding sites=7.85 and 7.2, respective dissociation constants of the internal and external Cl–-binding sites=160 and 40 m, and an additional, kinetically transparent, H+-binding site with a pK
a
>8.0. The quantitative model independently predicts the response ofJ
max andK
m
to acidic conditions.The results are discussed in terms of the general physiological requirement that fluxes through H+-coupled transport systems are relatively insensitive to environmental variation in pH
o
. It is proposed that (i) the weak (but finite) dependence of pH
c
on pH
o
, coupled with (ii) the strong dependence of H+-coupled transport on pH
c
are instrumental in endowing H+-coupled transport systems with a relative insensitivity to variation in pH
o
. This hypothesis might also explain why pH
c
in plants and fungi is not acutely controlled with respect to variation of pH
o
. 相似文献
14.
15.
Regulatory relationship and gain control between cytosolic free Ca2+ concentration (Cai) and cytosolic pH (pHi) were evaluated by two different cell types, gastric parietal cells, and blood platelets. Studies were carried out in both single cells and populations of cells, using Ca2+-indicative probe fura-2 (1-(2-(5′-carboxyoxazol-2′-yl)-6-aminobenzofuran-5-oxy)-2-(2′-amino-5′-methylphenoxy) ethane-N,N,N′,N′-tetraacetic acid) and pH-indicative probe BCECF (2′,7′-bis(carboxyethyl) carboxyfluorescein). Stimulation of single and populational parietal cells and platelets with gastrin and thrombin, respectively, resulted in an increase in Cai. In both populational cell types, an initial change in pHi during agonist stimulation occurred almost simultaneously with the mobilization of Ca2+; an initial transient decrease in pHi was followed by a slower increase in pHi above the prestimulation level. When populational platelets were preloaded with the Ca2+ chelator BAPTA (1,2-bis(o-aminophenoxy)ethane-N,N,N′,N′tetraacetic acid), the thrombin-induced initial large increase in Cai was apparently inhibited, whereas the pHi decrease induced by thrombin was not altered. This suggests that the initial Cai change is not a prerequisite for the pHi change. The effect of pHi on Cai was examined next. In both single and populational cell types, application of the K+-H+ ionophore nigericin, which induced a transient decrease in pHi, led to the release of Ca2+ from intracellular stores. In single parietal cells double-labeled with fura-2 and BCECF, a temporal decrease in pHi preceded the rise in Cai after stimulation with nigericin. A decrease in pHi, and an increase in Cai occurred at 1.5 and 4 s, respectively. In single parietal cells, replacement of medium Na+ with N-methyl-
-glucamine (NMG+), which also induced a decrease in pHi, resulted in repetitive Ca2+ spike oscillations. The source of Ca2+ utilized for the Ca2+ oscillation that was induced by NMG+ originated from the agonist-sensitive pool. Thus, several maneuvers, which were capable of decreasing pHi, led to an increase in Cai. Cytosolic acidification may be a part of the trigger for Ca2+ mobilization from intracellular stores in both parietal cells and platelets. 相似文献
16.
Ionic responses to alteration in external and internal pH were examined in an organism from a marine-like environment. Vacuolar pH (pHv) is about 4.9–5.1, constant at external pH (pHo) 5–8, while cytoplasmic pH (pHc) increases from 7.3 to 7.7. pHc regulation fails above pHo 9, and this is accompanied by failure of turgor regulation. Na+ increases above pHo 9, while K+ and Cl– decrease. These changes alone cannot however explain the alterations in turgor. Agents known to affect internal pH are also tested for their effect on ion relations.Abbreviations Ci
ion concentration
- CCCP
carbonyl cyanide m-chlorophenyl hydrazone
- DCCD
dicyclohexylcarbodiimide
- DES
diethylstilbestrol
- DMO
5,5-dimethyloxazolidine-2,4-dione
- DNP
2,4-dinitrophenol
- pHo
external pH
- pHc
cytoplasmic pH
- pHv
vacuolar pH
- i
osmotic pressure
-
turgor pressure 相似文献
17.
S. Y. Chow Y. C. Yen-Chow H. S. White L. Hertz D. M. Woodbury 《Neurochemical research》1991,16(12):1275-1283
Inastrocytes, as [K+]o was increased from 1.2 to 10 mM, [K+]i and [Cl–]i were increased, whereas [Na+]i was decreased. As [K+]o was increased from 10 to 60 mM, intracellular concentration of these three ions showed no significant change. When [K+]o was increased from 60 to 122 mM, an increase in [K+]i and [Cl–]i and a decrease in [Na+]i were observed.Inneurons, as [K+]o was increased from 1.2 to 2.8 mM, [Na+]i and [Cl–]i were decreased, whereas [K+]i was increased. As [K+]o was increased from 2.8 to 30 mM, [K+]i, [Na+]i and [Cl–]i showed no significant change. When [K+]o was increased from 30 to 122 mM, [K+]i and [Cl–]i were increased, whereas [Na+]i was decreased. Inastrocytes, pHi increased when [K+]o was increased. Inneurons, there was a biphasic change in pHi. In lower [K+]o (1.2–2.8 mM) pHi decreased as [K+]o increased, whereas in higher [K+]o (2.8–122 mM) pHi was directly related to [K+]o. In bothastrocytes andneurons, changes in [K+]o did not affect the extracellular water content, whereas the intracellular water content increased as the [K+]o increased. Transmembrane potential (Em) as measured with Tl-204 was inversely related to [K+]o between 1.2 and 90 mM, a ten-fold increase in [K+]o depolarized the astrocytes by about 56 mV and the neurons about 52 mV. The Em values measured with Tl-204 were close to the potassium equilibrium potential (Ek) except those in neurons at lower [K+]o. However, they were not equal to the chloride equilibrium potential (ECl) at [K+]o lower than 30 mM in both astrocytes and neurons. Results of this study demonstrate that alteration of [K+]o produced different changes in [K+]i, [Na+]i, [Cl–]i, and pHi in astrocytes and neurons. The data show that astrocytes can adapt to alterations in [K+]o, in such a way to maintain a more suitable environment for neurons. 相似文献
18.
Xiaohui Liu Shenguan Cai Gang Wang Feifei Wang Fabao Dong Michelle Mak Paul Holford Jing Ji Anya Salih Meixue Zhou Sergey Shabala Zhong-Hua Chen 《Plant Growth Regulation》2017,82(2):333-351
While the role of the vacuolar NHX Na+/H+ exchangers in plant salt tolerance has been demonstrated on numerous occasions, their control over cytosolic ionic relations has never been functionally analysed in the context of subcellular Na+ and K+ homeostasis. In this work, PutNHX1 and SeNHX1 were cloned from halophytes Puccinellia tenuiflora and Salicornia europaea and transiently expressed in Arabidopsis wild type Col-0 and the nhx1 mutant. Phylogentic analysis, topological prediction, analysis of evolutionary conservation, the topology structure and analysis of hydrophobic or polar regions of PutNHX1 and SeNHX1 indicated that they are unique tonoplast Na+/H+ antiporters with characteristics for salt tolerance. As a part of the functional assessment, cytosolic and vacuolar Na+ and K+ in different root tissues and ion fluxes from root mature zone of Col-0, nhx1 and their transgenic lines were measured. Transgenic lines sequestered large quantity of Na+ into root cell vacuoles and also promoted high cytosolic and vacuolar K+ accumulation. Expression of PutNHX1 and SeNHX1 led to significant transient root Na+ uptake in the four transgenic lines upon recovery from salt treatment. In contrast, the nhx1 mutant maintained a prolonged Na+ efflux and the nhx1:PutNHX1 and nhx1:SeNHX1 lines started to actively pump Na+ out of the cell. Overall, our findings suggest that PutNHX1 and SeNHX1 improve Na+ sequestration in the vacuole and K+ retention in the cytosol and vacuole of root cells of Arabidopsis, and that they interact with other regulatory mechanisms to provide a highly orchestrated regulation of ionic relations among intracellular cell compartments. 相似文献
19.
A. Bosia D. Ghigo F. Turrini E. Nissani G. P. Pescarmona H. Ginsburg 《Journal of cellular physiology》1993,154(3):527-534
Intraerythrocytic malaria parasites produce vast amounts of lactic acid through glycolysis. While the egress of lactate is very rapid, the mode of extrusion of H+ is not known. The possible involvement of a Na+/H+ antiport in the extrusion of protons across the plasma membrane of Plasmodium falciparum has been investigated by using the fluorescent pH probe 6-carboxyfluorescein. The resting cytosolic pH was 7.27 ± 0.1 in ring stage parasites and 7.31 ± 0.12 in trophozoites. Spontaneous acidification of parasite cytosol was observed in Na+-medium and realkalinization occurred upon addition of Na+ to the medium in a concentration-dependent manner, with no apparent saturation. The rate of H+-at the ring stage was higher than that at the trophozoite stage due to the larger surface/volume ratio of the young parasite stage. Na+-H+-was: 1) inhibited by the Na+/H+ inhibitors amiloride and 5-(N-ethyl-isopropyl) amiloride (EIPA), though at relatively high concentrations; 2) augmented with rising pH6 (pHi = 6.2 [Na+]o = 30 mM); and 3) decreased with increasing pHi (pHo = 7.4; [Na+]o = 30 mM). The pHi and the pHo dependencies of H+-were almost identical at all parasite stages. Only at pHi > 7.6 efflux was totally obliterated. The target of this inhibitory effect is probably other than the antiport. Results indicate that H+-is mediated by a Na+/H+ antiport which is regulated by host and parasite pH and by the host cytosol sodium concentration. The proton transport capacity of the antiport can easily cope with all the protons of lactic acid produced by parasite's glycolysis. © 1993 Wiley-Liss, Inc. 相似文献