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1.
Collet C Girbal L Péringer P Schwitzguébel JP Soucaille P 《Archives of microbiology》2006,185(5):331-339
The objective of the present study was to characterize the metabolism of Clostridium thermolacticum, a thermophilic anaerobic bacterium, growing continuously on lactose (10 g l−1) and to determine the enzymes involved in the pathways leading to the formation of the fermentation products. Biomass and metabolites concentration were measured at steady-state for different dilution rates, from 0.013 to 0.19 h−1. Acetate, ethanol, hydrogen and carbon dioxide were produced at all dilution rates, whereas lactate was detected only for dilution rates below 0.06 h−1. The presence of several key enzymes involved in lactose metabolism, including beta-galactosidase, glyceraldehyde-3-phosphate dehydrogenase, pyruvate:ferredoxin oxidoreductase, acetate kinase, ethanol dehydrogenase and lactate dehydrogenase, was demonstrated. Finally, the intracellular level of NADH, NAD+, ATP and ADP was also measured for different dilution rates. The production of ethanol and lactate appeared to be linked with the re-oxidation of NADH produced during glycolysis, whereas hydrogen produced should come from reduced ferredoxin generated during pyruvate decarboxylation. To produce more hydrogen or more acetate from lactose, it thus appears that an efficient H2 removal system should be used, based on a physical (membrane) or a biological approach, respectively, by cultivating C. thermolacticum with efficient H2 scavenging and acetate producing microorganisms. 相似文献
2.
Abstract
Background: During myocardial ischemia, accumulation of end products from anaerobic glycolysis (hydrogen ions (H+), lactate) can cause cellular injury, consequently affecting organ function. The cells' ability to buffer H+ (buffering capacity (BC)) plays an important role in ischemic tolerance. Age related differences in myocardial lactate and H+ accumulation (one hour of ischemia) as well as differences in BC, myoglobin (Mb) and histidine (His) contents in the left (LV) and right (RV) ventricles were assessed in neonatal compared to adult pigs. The BC of the septum was also compared. Methods and Results: Neonatal RV and LV had lactate accumulations of 43% and 63% and significantly greater H+ (p < 0.004) compared to the adult. In the neonate LV, BC was 17% significantly poorer (p = 0.0001), had 33% lower Mb (p = 0.0002) and 15% lower His content (p = 0.0004) when compared to the adult. In the RV, despite similar BC between the neonate and adult, myoglobin content was 36% (p = 0.0004) lower in the neonate. The neonate septum had a BC that was 11% lower than that of the adult. With maturation, the adult LV had a BC that was 10% greater (p < 0.01) than the RV while the septum mirrored that of the LV. Conclusions: During maturation to adulthood, the BC of the septum begins to closely resemble the LV. Neonatal hearts have a potentially greater vulnerability to acid-base disturbances during ischemia in both ventricles when compared to hearts of adults. This is due to lower levels of myoglobin and histidine in the young, which could render them more susceptible to injury during ischemia.Condensed Abstract During myocardial ischemia, H+ and lactate accumulation may pose deleterious effects on the heart. The ability to buffer H+ (buffering capacity, BC) affects ischemic tolerance. Although lactate accumulation during 1 h of global ischemia was similar between ventricles of neonatal and adult swine, H+ accumulation was greater and BC, Mb and His content were lower. With maturation, LV BC was higher than the RV while septum developmentally resembled the LV. Thus, hearts of neonates may be at a greater risk of ischemic injury compared to hearts of adults. (Mol Cell Biochem xxx: 1–7, 2005) 相似文献
3.
Warren DE Jackson DC 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》2008,178(2):133-148
Painted turtles can accumulate lactic acid to extremely high concentrations during long-term anoxic submergence, with plasma
lactate exceeding 200 mmol l−1. The aims of this review are twofold: (1) To summarize aspects of lactate metabolism in anoxic turtles that have not been
reviewed previously and (2) To identify gaps in our knowledge of turtle lactate metabolism by comparing it with lactate metabolism
during and after exercise in other vertebrates. The topics reviewed include analyses of lactate’s fate during recovery, the
effects of temperature on lactate accumulation and clearance, the interaction of activity and recovery metabolism, fuel utilization
during recovery, stress hormone responses during and following anoxia, and cellular lactate transport mechanisms. An analysis
of lactate metabolism in anoxic turtles in the context of the ‘lactate shuttle’ hypothesis is also presented. 相似文献
4.
Jensen FB Koldkjaer P Bach A 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》2000,170(7):489-495
Nitrite influx into crayfish showed saturation kinetics, supporting a carrier-mediated uptake. Addition of 4,4′-diisothiocyanatostilbene-2,2′-disulfonate
(DIDS: at 10−5, 10−4 and 10−3 M) and bumetanide (at 10−5 M and 10−4 M) to the ambient water did not significantly affect nitrite influx. Rather than suggesting that neither Cl−/HCO3
− exchange nor K+/Na+/2Cl− cotransport were involved in the transport, this may reflect that the gill cuticle has a low permeability to the pharmacological
agents, or that the sensitivity of the transport mechanism to the inhibitors is low. Nitrite accumulation in the haemolymph
was significantly decreased during hypercapnic conditions compared to normocapnic conditions. This supports the idea that
an acid–base regulatory decrease in Cl−(influx)/HCO3
− (efflux) induced by hypercapnia should decrease NO2
− uptake if NO2
− and Cl− share this uptake route. The respiratory acidosis caused by exposure to hypercapnia alone was partially compensated by HCO3
− accumulation in the haemolymph. Combined exposure to hypercapnia and nitrite improved pH recovery, mainly by augmenting the
[HCO3
−] increase, but also by decreasing haemolymph PCO2. Exposure to nitrite in normocapnic water induced an initial increase in haemolymph [HCO3
−] and later also a decrease in PCO2. Thus, the improved acid-base compensation during combined hypercapnia and nitrite exposure was an amplification of this
nitriteinduced response. Haemolymph base excess rose much more than haemolymph [Ca], suggesting that transfer of acid-base
equivalents between animal and water was more important than H+ buffering by exoskeletal CaCO3 in mediating the increase in haemolymph [HCO3
−].
Accepted: 27 June 2000 相似文献
5.
MDCK cells display several acid-base transport systems found in intercalated cells, such as Na+-H+ exchange, H+–K+ ATPase and Cl−/HCO−
3 exchange. In this work we studied the functional activity of a vacuolar H+-ATPase in MDCK cells and its chloride dependence. We measured intracellular pH (pHi) in monolayers grown on glass cover slips
utilizing the pH sensitive probe BCECF. To analyze the functional activity of the H+ transporters we observed the intracellular alkalinization in response to an acute acid load due to a 20 mm NH+
4 pulse, and calculated the initial rate of pHi recovery (dpHi/dt). The cells have a basal pHi of 7.17 ± 0.01 (n= 23) and control dpHi/dt of 0.121 ± 0.006 (n= 23) pHi units/min. This pHi recovery rate is markedly decreased when Na+ was removed, to 0.069 ± 0.004 (n= 16). It was further reduced to 0.042 ± 0.005 (n= 12) when concanamycin 4.6 × 10−8
m (a specific inhibitor of the vacuolar H+-ATPase) was added to the zero Na+ solution. When using a solution with zero Na+, low K+ (0.5 mm) plus concanamycin, pHi recovery fell again, significantly, to 0.023 ± 0.006 (n= 14) as expected in the presence of a H+–K+-ATPase. This result was confirmed by the use of 5 × 10−5
m Schering 28080. The Na+ independent pHi recovery was significantly reduced from 0.069 ± 0.004 to 0.042 ± 0.004 (n= 12) when NPPB 10−5
m (a specific blocker of Cl− channels in renal tubules) was utilized. When the cells were preincubated in 0 Cl−/normal Na+ solution for 8 min. before the ammonium pulse, the pHi recovery fell from 0.069 ± 0.004 to 0.041 ± 0.007 (n= 12) in a Na+ and Cl− free solution. From these results we conclude that: (i) MDCK cells have two Na+-independent mechanisms of pHi recovery, a concanamycin sensitive H+-ATPase and a K+ dependent, Schering 28080 sensitive H+–K+ ATPase; and, (ii) pHi recovery in Na+-free medium depends on the presence of a chloride current which can be blocked by NPPB and impaired by preincubation in Cl−–free medium. This finding supports a role for chloride in the function of the H+ ATPase, which might be electrical shunting or a biochemical interaction.
Received: 24 October 1997/Revised: 19 February 1998 相似文献
6.
Hirono C Nakamoto T Sugita M Iwasa Y Akagawa Y Shiba Y 《The Journal of membrane biology》2001,180(1):11-19
Forskolin-induced anion currents and depolarization were investigated to clarify the mechanism of HCO3
− secretion in the intralobular duct cells of rat parotid glands. Anion currents of the cells were measured at the equilibrium
potential of K+, using a gramicidin-perforated patch technique that negligibly affects intracellular anion concentration. The forskolin-induced
anion current was sustained and significantly (54%) suppressed by glibenclamide (200 μm), a blocker of the cystic fibrosis transmembrane conductance regulator (CFTR) Cl− channel. The anion current was markedly suppressed by addition of 1 mm methazolamide, a carbonic anhydrase inhibitor, and removal of external HCO3
−. Forskolin depolarized the cells in the current-clamp mode. Addition of methazolamide and removal of external HCO3
− significantly decreased the depolarizing level. These results suggest that activation of anion channels (mainly the CFTR
Cl− channel located in luminal membranes) and production of cytosolic HCO3
− induce the inward anion current and resulting depolarization. Inhibition of the Na+-K+-2Cl− cotransporter and the Cl−-HCO3
− exchanger had no significant effect on the current or depolarization, indicating that the uptake of Cl− via the Na+-K+-2Cl− cotransporter or the Cl−-HCO3
− exchanger is not involved in the responses. Taken together, we conclude that forskolin activates the outward movement (probably
secretion) of HCO3
− produced intracellularly, but not of Cl− due to lack of active Cl− transport in parotid duct cells, and that the gramicidin-perforated patch method is very useful to analyze anion transport.
Received: 17 June 2000/Revised: 14 November 2000 相似文献
7.
Wood CM Pärt P 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》2000,170(3):175-184
The influence of a CO2/HCO−
3-buffered medium on intracellular pH regulation of gill pavement cells from freshwater rainbow trout was examined in monolayers
grown in primary culture on glass coverslips; intracellular pH (pHi) was monitored by continuous spectrofluorometric recording from cells loaded with 2′,7′-bis(2-carboxyethyl)-5(6)-carboxy-fluoroscein. When cells in HEPES-buffered medium at normal pH=7.70 were transferred to normal
CO2/HCO−
3-buffered medium {P
CO2=3.71 mmHg, [HCO−
3]= 6.1 mmol l−1, extracellular pH (pHe)=7.70}, they exhibited a brief acidosis but subsequently regulated the same pHi (∼7.41) as in HEPES. Buffer capacity (β)
increased by the expected amount (5.5–8.0 slykes) based on intracellular [HCO−
3], and was unaffected by most drugs and treatments. However, after transfer to high P
CO2=11.15 mmHg, [HCO−
3]= 18.2 mmol l−1 at the same pHe=7.70, the final regulated pHi was elevated (∼7.53). The rate of correction of alkalosis caused by washout of this high P
CO2, high-HCO−
3 medium was unaffected by removal of extracellular Cl−. Removal of extracellular Na+ lowered resting pHi and greatly inhibited the rate of pHi recovery from acidosis. Bafilomycin A1 (3 μmol l−1) had no effect on these responses. However amiloride (0.2 mmol l−1) inhibited recovery from acidosis caused by washout of an ammonia prepulse, but did not affect resting pHi, the latter differing from the response in HEPES where amiloride also lowered resting pHi. Similarly 4-acetamido-4′- isothiocyanatostilbene-2,2′-disulfonic acid, sodium salt (0.1 mmol l−1) did not affect resting pHi but slowed the rate of recovery from acidosis, though to a lesser extent than amiloride. Removal of extracellular Cl− also slowed the rate of recovery but greatly increased β by an unknown mechanism; when this was taken into account, H+ extrusion rate was unaffected. These results are consistent with the presence of Na+-(HCO−
3)N co-transport and/or Na+-dependent HCO−
3/Cl− exchange, in addition to Na+/H+ exchange, as mechanisms contributing to “housekeeping” pHi regulation in gill cells in CO2/HCO−
3 media, whereas only Na+/H+ exchange is seen in HEPES. Both Na+-independent Cl−/HCO−
3 exchange and V-type H+-ATPase mechanisms appear to be absent from these cells cultured in isotonic media.
Accepted: 30 November 1999 相似文献
8.
Torres ML Ortega F Cuaranta I González J Sanchez-Armass S 《Neurochemical research》2008,33(8):1574-1581
The Na+/H+ exchanger has been the only unequivocally demonstrated H+-transport mechanism in the synaptosomal preparation. We had previously suggested that a Cl−–H+ symporter (in its acidifying mode) is involved in cytosolic pH regulation in the synaptosomal preparation. Supporting this
suggestion, we now show that: (1) when synaptosomes are transferred from PSS to either gluconate or sulfate solutions, the
Fura-2 ratio remains stable instead of increasing as it does in 50 mM K solution. This indicates that these anions do not
promote a plasma membrane depolarization. (2) Based in the recovery rate from the cytosolic alkalinization, the anionic selectivity
of the Cl−–H+ symporter is NO3− > Br− > Cl− >> I− = isethionate = sulfate = methanesulfonate = gluconate. (3) PCMB 10 μM inhibits the gluconate-dependent alkalinization by
30 ± 6%. (4) Neither Niflumic acid, 9AC, Bumetanide nor CCCP inhibits the recovery from the cytosolic alkalinization.
Special issue article in honor of Dr. Ricardo Tapia. 相似文献
9.
A mathematical model of the HCO−
3-secreting pancreatic ductal epithelium was developed using network thermodynamics. With a minimal set of assumptions, the
model accurately reproduced the experimentally measured membrane potentials, voltage divider ratio, transepithelial resistance
and short-circuit current of nonstimulated ducts that were microperfused and bathed with a CO2/HCO−
3-free, HEPES-buffered solution, and also the intracellular pH of duct cells bathed in a CO2/HCO−
3-buffered solution. The model also accurately simulated: (i) the effect of step changes in basolateral K+ concentration, and the effect of K+ channel blockers on basolateral membrane potential; (ii) the intracellular acidification caused by a Na+-free extracellular solution and the effect of amiloride on this acidification; and (iii) the intracellular alkalinization
caused by a Cl−-free extracellular solution and the effect of DIDS on this alkalinization. In addition, the model predicted that the luminal
Cl− conductance plays a key role in controlling both the HCO−
3 secretory rate and intracellular pH during HCO−
3 secretion. We believe that the model will be helpful in the analysis of experimental data and improve our understanding of
HCO−
3-transporting mechanisms in pancreatic duct cells.
Received: 18 October 1995/Revised: 5 July 1996 相似文献
10.
Kummerow D Hamann J Browning JA Wilkins R Ellory JC Bernhardt I 《The Journal of membrane biology》2000,176(3):207-216
The change of intracellular pH of erythrocytes under different experimental conditions was investigated using the pH-sensitive
fluorescent dye BCECF and correlated with (ouabain + bumetanide + EGTA)-insensitive K+ efflux and Cl− loss. When human erythrocytes were suspended in a physiological NaCl solution (pH
o
= 7.4), the measured pH
i
was 7.19 ± 0.04 and remained constant for 30 min. When erythrocytes were transferred into a low ionic strength (LIS) solution,
an immediate alkalinization increased the pH
i
to 7.70 ± 0.15, which was followed by a slower cell acidification. The alkalinization of cells in LIS media was ascribed
to a band 3 mediated effect since a rapid loss of approximately 80% of intracellular Cl− content was observed, which was sensitive to known anion transport inhibitors. In the case of cellular acidification, a comparison
of the calculated H+ influx with the measured unidirectional K+ efflux at different extracellular ionic strengths showed a correlation with a nearly 1:1 stoichiometry. Both fluxes were
enhanced by decreasing the ionic strength of the solution resulting in a H+ influx and a K+ efflux in LIS solution of 108.2 ± 20.4 mmol (l
cells
hr)−1 and 98.7 ± 19.3 mmol (l
cells
hr)−1, respectively. For bovine and porcine erythrocytes, in LIS media, H+ influx and K+ efflux were of comparable magnitude, but only about 10% of the fluxes observed in human erythrocytes under LIS conditions.
Quinacrine, a known inhibitor of the mitochondrial K+(Na+)/H+ exchanger, inhibited the K+ efflux in LIS solution by about 80%. Our results provide evidence for the existence of a K+(Na+)/H+ exchanger in the human erythrocyte membrane.
Received: 22 December 1999/Revised: 10 April 2000 相似文献
11.
T. Wang P. K. Knudsen C. J. Brauner M. Busk M. M. Vijayan F. B. Jensen 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1998,168(8):591-599
In order to evaluate the impact of water-borne copper on acid-base regulation in fresh water rainbow trout, chronically cannulated
fish were exposed to copper (0.6 mg 1−1), hypercapnia (water PCO2 of 6 mmHg) or a combination of copper and hypercapnia, while a fourth untreated group served as the control. Blood samples
obtained at 0 h, 4 h and 24 h were analysed for acid-base status, ion concentrations and respiratory parameters. Tissue samples
from caudal skeletal muscle, liver and gill filaments were examined for intracellular acid-base status, ion- and water contents,
and copper concentration. Exposure to copper alone elicited a small extracellular metabolic alkalosis, no changes in arterial
PO2, and a minor decrease in plasma ion concentrations. Hypercapnia alone increased arterial PCO2 from approximately 2 mmHg to 7.2 mmHg, but the extracellular respiratory acidosis present at 4 h was almost completely compensated
at 24 h due to an increase in plasma bicarbonate concentration [HCO3
−] from 8.1 mM to 24.4 mM. Combined exposure to hypercapnia and copper resulted in a slightly larger acidosis at 4 h, and the
fish failed to restore extracellular pH at 24 h, because plasma [HCO3
−] only increased to 16.3 mM. Fish exposed to hypercapnia and copper also showed a delayed recovery of intracellular pH in
skeletal muscle, compared to fish exposure to hypercapnia only. Thus, copper exposure impaired both extracellular and intracellular
acid-base regulation during hypercapnia. When seen in connection with only minor effects of copper on osmoregulatory and respiratory
parameters, the reduced ability to regulate acid-base suggests that acid-base regulation may be one of the most copper-sensitive
branchial functions.
Accepted: 18 August 1998 相似文献
12.
L-lactate transport mechanism across rat jejunal enterocyte was investigated using isolated membrane vesicles. In basolateral
membrane vesicles l-lactate uptake is stimulated by an inwardly directed H+ gradient; the effect of the pH difference is drastically reduced by FCCP, pCMBS and phloretin, while furosemide is ineffective.
The pH gradient effect is strongly temperature dependent. The initial rate of the proton gradient-induced lactate uptake is
saturable with respect to external lactate with a K
m
of 39.2 ± 4.8 mm and a J
max of 8.9 ± 0.7 nmoles mg protein−1 sec−1. A very small conductive pathway for l-lactate is present in basolateral membranes. In brush border membrane vesicles both Na+ and H+ gradients exert a small stimulatory effect on lactate uptake. We conclude that rat jejunal basolateral membrane contains
a H+-lactate cotransporter, whereas in the apical membrane both H+-lactate and Na+-lactate cotransporters are present, even if they exhibit a low transport rate.
Received: 22 October 1996/Revised: 11 March 1997 相似文献
13.
S.F. Pedersen B. Kramhøft N.K. Jørgensen E.K. Hoffmann 《The Journal of membrane biology》1996,149(2):141-159
Amiloride-sensitive, Na+-dependent, DIDS-insensitive cytoplasmic alkalinization is observed after hypertonic challenge in Ehrlich ascites tumor cells.
This was assessed using the fluorescent pH-sensitive probe 2′,7′-bis-(2-carboxyethyl)-5,6-carboxyfluorescein (BCECF). A parallel
increase in the amiloride-sensitive unidirectional Na+ influx is also observed. This indicates that hypertonic challenge activates a Na+/H+ exchanger. Activation occurs after several types of hypertonic challenge, is a graded function of the osmotic challenge,
and is temperature-dependent. Observations on single cells reveal a considerable variation in the shrinkage-induced changes
in cellular pH
i
, but the overall picture confirms the results from cell suspensions.
Shrinkage-induced alkalinization and recovery of cellular pH after an acid load, is strongly reduced in ATP-depleted cells.
Furthermore, it is inhibited by chelerythrine and H-7, inhibitors of protein kinase C (PKC). In contrast, Calyculin A, an
inhibitor of protein phosphatases PP1 and PP2A, stimulates shrinkage-induced alkalinization.
Osmotic activation of the exchanger is unaffected by removal of calcium from the experimental medium, and by buffering of
intracellular free calcium with BAPTA.
At 25 mm HCO−
3, but not in nominally HCO−
3-free medium, Na+/H+ exchange contributes significantly to regulatory volume increase in Ehrlich cells.
Under isotonic conditions, the Na+/H+ exchanger is activated by ionomycin, an effect which may be secondary to ionomycin-induced cell shrinkage.
Received: 2 March 1995/Revised: 29 September 1995 相似文献
14.
Serge Ostrovidov Patricia Franck Josette Capiaumont Brigitte Dousset Francine Belleville 《In vitro cellular & developmental biology. Animal》1998,34(3):259-264
Summary The effect of low concentrations of hydrogen peroxide (H2O2) (5 × 10−7−9.5 × 10−7
M) on cell growth and antibody production was investigated with murine hybridoma cells (Mark 3 and anti-hPL) in culture. Cell
growth, measured by flow cytometry with morphological parameters, was significantly stimulated by H2O2 (8 × 10−7
M) but H2O2 concentration of 7 × 10−6
M and above increased cell death. H2O2 stimulation of antibody production was nonsignificant. The metabolism of cells treated with 8 × 10−7 or 1 × 10−5
M H2O2 was similar to that of the control in terms of glucose and glutamine consumption, lactate and ammonia production, and amino
acid concentrations in the medium. The concentrations of lactate dehydrogenase, a marker of cell death, in test and control
cells were similar. However, concentrations of intracellular free radicals measured by flow cytometry with dihydrorhodamine
123 (DHR 123) and dichlorofluorescein diacetate (DCFH-DA) as fluorochromes were different. The reactive oxygen species content
of cells in 8 × 10−7
M H2O2 was similar to that of the controls, but there was a sudden, marked production of superoxide anions (detected with DHR 123)
and H2O2 or peroxides (detected with DCFH-DA) by cells incubated with 1 × 10−5
M H2O2 which increased with increasing H2O2 until cell death. 相似文献
15.
Tubular Fluid Secretion in the Seminiferous Epithelium: Ion Transporters and Aquaporins in Sertoli Cells 总被引:1,自引:0,他引:1
Luís Rato Sílvia Socorro José E. B. Cavaco Pedro F. Oliveira 《The Journal of membrane biology》2010,236(2):215-224
Sertoli cells play a key role in the establishment of an adequate luminal environment in the seminiferous tubules of the male
reproductive tract. Secretion of the seminiferous tubular fluid (STF) is vital for the normal occurrence of spermatogenesis
and for providing a means of transport to the developing spermatozoa. However, several studies on this subject have not completely
clarified the origin and composition of this fluid. Electrolyte and water are central components of STF. Sertoli cells secrete
an iso-osmotic fluid with a higher content of K+ than the blood and express various membrane and water transporters (Na+/K+-ATPase; Ca2+-ATPase; V-type ATPase; Cl− channels; CFTR Cl− channels; K+ channels; L-, T- and N-type Ca2+ channels; Na+/H+ exchangers; Na+-driven HCO3
−/Cl− exchangers (NDCBEs); Na+/HCO3
− cotransporters (NBCes); Na+–K+–2Cl− cotransporter; Na+/Ca2+ exchanger; and aquaporins 0 and 8) involved in cellular and secretory functions. Studies with knockout mice for some of these
transporters showed tubular fluid accumulation and associated infertility, revealing the relevance of these processes for
the normal occurrence of spermatogenesis. Nevertheless, the role of the several membrane transporters in the establishment
of STF electrolyte composition needs to be further elucidated. This review summarizes the available data on the ionic composition
of STF and on the Sertoli cell membrane mechanisms responsible for ion and water movement. Deepening the knowledge on the
mechanisms involved in the secretion, composition and regulation of SFT is essential and will be a major step in understanding
the infertility associated with some pathological conditions. 相似文献
16.
Although both amiloride- and phloretin-sensitive Na+/Li+ exchange activities have been reported in mammalian red blood cells, it is still unclear whether or not the two are mediated
by the same pathway. Also, little is known about the relative contribution of these transport mechanisms to the entry of therapeutic
concentrations of Li+ (0.2–2 mm) into cells other than erythrocytes. Here, we describe characteristics of these transport systems in rat isolated hepatocytes
in suspension. Uptake of Li+ by hepatocytes, preloaded with Na+ and incubated in the presence of ouabain and bumetanide, comprised three components. (a) An amiloride-sensitive component, with apparent K
m
1.2 mm Li+, V
max
40 μmol · (kg dry wt · min)−1, showed increased activity at low intracellular pH. The relationship of this component to the concentration of intracellular
H+ was curvilinear suggesting a modifier role of [H+]
i
. This system persisted in Na+-depleted cells, although with apparent K
m
3.8 mm. (b) A phloretin-sensitive component, with K
m
1.2 mm, V
max
21 μmol · (kg · min)−1, was unaffected by pH but was inactive in Na+-depleted cells. Phloretin inhibited Li+ uptake and Na+ efflux in parallel. (c) A residual uptake increased linearly with the external Li+ concentration and represented an increasing proportion of the total uptake. The results strongly suggest that the amiloride-sensitive
and the phloretin-sensitive Li+ uptake in rat liver are mediated by two separate pathways which can be distinguished by their sensitivity to inhibitors and
intracellular [H+].
Received: 8 April 1999/Revised: 19 July 1999 相似文献
17.
Aporn Bualuang Kanteera Soontharapirakkul Aran Incharoensakdi 《Journal of applied phycology》2010,22(2):123-129
The activity of Na+/H+ exchanger to remove toxic Na+ is important for growth of organisms under high salinity. In this study, the halotolerant cyanobacterium Aphanothece halophytica was shown to possess Na+/H+ exchange activity since exogenously added Na+ could dissipate a pre-formed pH gradient, and decrease extracellular pH. Kinetic analysis yielded apparent K
m (Na+) and V
max of 20.7 ± 3.1 mM and 3,333 ± 370 nmol H+ min−1 mg−1, respectively. For cells grown under salt-stress condition, the apparent K
m (Na+) and V
max was 18.3 ± 3.5 mM and 3,703 ± 350 nmol H+ min−1 mg−1, respectively. Three cations with decreasing efficiency namely Li+, Ca2+, and K+ were also able to dissipate pH gradient. Only marginal exchange activity was observed for Mg2+. The exchange activity was strongly inhibited by Na+-gradient dissipators, monensin, and sodium ionophore as well as by CCCP, a protonophore. A. halophytica showed high Na+/H+ exchange activity at neutral and alkaline pH up to pH 10. Cells grown at pH 7.6 under high salinity exhibited higher Na+/H+ exchange activity than those grown under low salinity during 15 days of growth suggesting a role of Na+/H+ exchanger for salt tolerance in A. halophytica. Cells grown at alkaline pH of 9.0 also exhibited a progressive increase of Na+/H+ exchange activity during 15 days of growth. 相似文献
18.
In this study, the effects of Cd on root growth, respiration, and transmembrane electric potential (E
m) of the outer cortical cells in maize roots treated with various Cd concentrations (from 1 μM to 1 mM) for several hours
to one week were studied. The E
m values of root cells ranged between −120 and −140 mV and after addition of Cd they were depolarized immediately. The depolarization
was concentration-dependent reaching the value of diffusion potential (E
D) when the Cd concentration exceeded 100 μM. The values of E
D ranged between −65 to −68 mV (−66 ± 1.42 mV). The maximum depolarization of E
m was registered approx. 2.5 h after addition of Cd to the perfusion solution and in some cases, partial (Cd > 100 μM) or complete
repolarization (Cd < 100 μM) was observed within 8–10 h of Cd treatment. In the time-dependent experiments (0 to 168 h) shortly
after the maximum repolarization of E
m a continuous concentration-dependent decrease of E
m followed at all Cd concentrations. Depolarization of E
m was accompanied by both increased electrolyte leakage and inhibition of respiration, especially in the range of 50 μM to
1 mM Cd, with the exception of root cells treated with 1 and 10 μM Cd for 24 and 48 h. Time course analysis of Cd impact on
root respiration revealed that at higher Cd concentrations (> 50 μM) the respiration gradually declined (∼ 6 h) and then remained
at this lowest level for up to 24 h.
All the Cd concentrations used in this experiment induced significant inhibition of root elongation and concentrations higher
than 100 μM stopped the root growth within the first day of Cd treatment. Our results suggest that Cd does not cause irreversible
changes in the electrogenic plasma membrane H+ ATPase because fusicoccin, an H+ ATPase activator diminished the depolarizing effect of Cd on the E
m. The depolarization of E
m in the outer cortical cells of maize roots was the result of a cumulative effect of Cd on ATP supply, plasmalemma permeability,
and activity of H+ ATPase. 相似文献
19.
Cell pH regulation was investigated in the T84 cell line derived from epithelial colon cancer. Cell pH was measured by ratiometric
fluorescence microscopy using the fluorescent probe BCECF. Basal pH was 7.17 ± 0.023 (n= 48) in HEPES Ringer. After acidification by an ammonium pulse, cell pH recovered toward normal at a rate of 0.13 ± 0.011
pH units/min in the presence of Na+, but in the absence of this ion or after treatment with 0.1 mm hexamethylene amiloride (HMA) no significant recovery was observed, indicating absence of Na+ independent H+ transport mechanisms in HEPES Ringer. In CO2/HCO−
3 Ringer, basal cell pH was 7.21 ± 0.020 (n= 35). Changing to HEPES Ringer, a marked alkalinization was observed due to loss of CO2, followed by return to the initial pH at a rate of −0.14 ± 0.012 (n= 8) pH/min; this return was retarded or abolished in the absence of Cl− or after addition of 0.2 mm DIDS, suggesting extrusion of bicarbonate by Cl−/HCO−
3 exchange. This exchange was not Na+ dependent. When Na+ was added to cells incubated in 0 Na+ Ringer while blocking Na+/H+ exchange by HMA, cell alkalinization by 0.19 ± 0.04 (n= 11) pH units was observed, suggesting the presence of Na+/HCO−
3 cotransport carrying HCO−
3 into these cells, which was abolished by DIDS. These experiments, thus, show that Na+/H+ and Cl−/HCO−
3 exchange and Na+/HCO−
3 cotransport participate in cell pH regulation in T84 cells.
Received: 3 April 2000/Revised: 22 June 2000 相似文献
20.
Koop JH Grieshaber MK 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》2000,170(1):75-83
Fluctuating salinities at different sites on the German salt-polluted rivers Werra and Weser were compared with extracellular
ion levels of specimens of Gammarus tigrinus (Sexton; Amphipoda, Crustacea), collected at the same sites. G. tigrinus regulated haemolymph concentrations of inorganic anions (Cl−, SO2−
4, PO3−
4) and cations (Na+, K+, Mg2+, Ca2+) during fluctuations of salt pollution in the upper Weser. This capacity to regulate varying levels of salt pollution in
the upper Weser, correlated well with the distribution of the brackish amphipods in this river ecosystem. G. tigrinus tolerated periods of Na+ and Cl− stress (>380 mmol l−1) without compensating these maxima by regulating extracellular Na+ and Cl−. However, during such bursts of Na+ and Cl− stress in Werra and Weser, the ability to regulate extracellular [K+] at river water K+ stress of ≥6.0 mmol l−1 may explain why this brackish species has been more successful in these rivers than its competitors like Gammarus pulex. The present investigation demonstrates that the water salinity affects the [NO−
3] in the haemolymph of G. tigrinus. With increasing hypo-osmotic stress the animals accumulate increasing amounts of NO−
3. A simultaneous increase in stream water [NO−
3] causes an additional accumulation of NO−
3 in the haemolymph. The high extent of accumulation indicates that active ion transport systems may be involved. The accumulation
of NO−
3 in the haemolymph has low physiological consequences to G. tigrinus, but when hypo-osmotically stressed under anoxic conditions, nitrite formed by the reduction of nitrate may have an adverse
affect on the metabolism of G. tigrinus.
Accepted: 4 October 1999 相似文献