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1.
Nitrogen metabolism by heterotrophic bacterial assemblages in Antarctic coastal waters 总被引:4,自引:0,他引:4
Field studies to examine the in situ assimilation and production of ammonium (NH4
+) by bacterial assemblages were conducted in the northern Gerlache Strait region of the Antarctic Peninsula. Short term incubations of surface waters containing 15N-NH4
+ as a tracer showed the bacterial population taking up 0.041–0.128 g-atoms Nl–1d–1, which was 8–25% of total NH4
+ uptake rates. The large bacterial uptake of NH4
+ occurred even at low bacterial abundance during a rich phytoplankton bloom. Estimates of bacterial production using 3H-leucine and -adenine were l.0gCl–1 d–1 before the bloom and 16.2 g Cl–1 d–1 at the bloom peak. After converting bacterial carbon production to an estimate of nitrogen demand, NH4
+ was found to supply 35–60% of bacterial nitrogen requirements. Bacterial nitrogen demand was also supported by dissolved organic nitrogen, generally in the form of amino acids. It was estimated, however, that 20–50% of the total amino acids taken up were mineralized to NH4
+. Bacterial production of NH4
+ was occurring simultaneously to its uptake and contributed 27–55% of total regenerated NH4
+ in surface waters. Using a variety of 15N-labelled amino acids it was found that the bacteria metabolized each amino acid differently. With their large mineralization of amino acids and their relatively low sinking rates, bacteria appear to be responsible for a large portion of organic matter recycling in the upper surface waters of the coastal Antarctic ecosystem. 相似文献
2.
D. Delille 《Polar Biology》1987,8(1):55-60
Summary Previous antarctic studies have pointed out the ecological importance of ornithogenic soils. However, few data exist to determine the impact of such guanoenriched soils on surrounding seawater microbial populations. In order to evaluate the influence of birds, the relationships of spatial distribution of seawater bacterial microflora to penguin repartition were studied during the antarctic summer 1986 in Terre Adelie land area and in January 1984 in the subantarctic Kerguelen Archipelago. With bacterial estimates as high as 1.7×108 cells ml-1 for total counts and 2.3×107 CFU ml-1 for aerobic heterotrophic populations, ornithogenic soil analyses confirmed previous results from similar sites. In seawater a clear decreasing gradient from the shore towards the open sea was found. All bacterial parameters studied (epifluorescence direct counts, frequency of dividing cells estimation and viable counts) were correlated significantly with penguin populations. Complementary numerical taxonomy confirmed the major role played by the bird manuring in such antarctic ecosystems. 相似文献
3.
Summary The Na+ requirement for active, electrogenic Cl– absorption byAmphiuma small intestine was studied by tracer techniques and double-barreled Cl–-sensitive microelectrodes. Addition of Cl– to a Cl–-free medium bathingin vitro intestinal segments produced a saturable (K
m
=5.4mm) increase in shortcircuit current (I
sc) which was inhibitable by 1mm SITS. The selectivity sequence for the anion-evoked current was Cl–=Br–>SCN–>NO
3
–
>F–=I–. Current evoked by Cl– reached a maximum with increasing medium Na concentration (K
m
=12.4mm). Addition of Na+, as Na gluconate (10mm), to mucosal and serosal Na+-free media stimulated the Cl– current and simultaneously increased the absorptive Cl– flux (J
ms
Cl
) and net flux (J
net
Cl
) without changing the secretory Cl– flux (J
sm
Cl
). Addition of Na+ only to the serosal fluid stimulatedJ
ms
Cl
much more than Na+ addition only to the mucosal fluid in paired tissues. Serosal DIDS (1mm) blocked the stimulation. Serosal 10mm Tris gluconate or choline gluconate failed to stimulateJ
ms
Cl
. Intracellular Cl– activity (a
Cl
i
) in villus epithelial cells was above electrochemical equilibrium indicating active Cl– uptake. Ouabain (1mm) eliminated Cl– accumulation and reduced the mucosal membrane potential
m
over 2 to 3 hr. In contrast, SITS had no effect on Cl– accumulation and hyperpolarized the mucosal membrane. Replacement of serosal Na+ with choline eliminated Cl– accumulation while replacement of mucosal Na+ had no effect. In conclusion by two independent methods active electrogenic Cl– absorption depends on serosal rather than mucosal Na+. It is concluded that Cl– enters the cell via a primary (rheogenic) transport mechanism. At the serosal membrane the Na+ gradient most likely energizes H+ export and regulates mucosal Cl– accumulation perhaps by influencing cell pH or HCO
3
–
concentration. 相似文献
4.
Hiroshi Miyamoto Toshitaka Ikehara Hisao Yamaguchi Keiko Hosokawa Takeo Yonezu Toshio Masuya 《The Journal of membrane biology》1986,92(2):135-150
Summary Ouabain-insensitive, furosemide-sensitive Rb+ influx (J
Rb) into HeLa cells was examined as functions of the extracellular Rb+, Na+ and Cl– concentrations. Rate equations and kinetic parameters, including the apparent maximumJ
Rb, the apparent values ofK
m for the three ions and the apparentK
i for K+, were derived. Results suggested that one unit molecule of this transport system has one Na+, one K+ and two Cl– sites with different affinities, one of the Cl– sites related with binding of Na+, and the other with binding of K+(Rb+). A 11 stoichiometry was demonstrated between ouabain-insensitive, furosemidesensitive influxes of22Na+ and Rb+, and a 12 stoichiometry between those of Rb+ and36Cl–. The influx of either one of these ions was inhibited in the absence of any one of the other two ions. Monovalent anions such as nitrate, acetate, thiocyanate and lactate as substitutes for Cl– inhibited ouabain-insensitive Rb+ influx, whereas sulfamate and probably also gluconate did not inhibitJ
Rb. From the present results, a general model and a specialized cotransport model were proposed: 1) In HeLa cells, one Na+ and one Cl– bind concurrently to their sites and then one K+ (Rb+) and another Cl– bind concurrently. 2) After completion of ion bindings Na+, K+(Rb–) and Cl– in a ratio of 112 show synchronous transmembrane movements. 相似文献
5.
David H. Thomas Erik Skadhauge 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1989,159(1):51-60
Summary The function of the caecal bulb, and its adaptation to chronic high- or low-Na+ intake, was investigated by in vivo perfusion of anaesthetised birds. Effects of acute aldosterone injection (125 g·kg–1 body mass) were also measured.Evidence was found for primary active net absorption of Na+, inducing parallel Na-linked absorption of water and Cl– and secretion of K+. Around 20–35% of total Cl– absorption and K+ secretion were independent of Na+ fluxes, and these components appear to be driven by passive processes with apparent conductances of 6.3×10–3 (G
Cl) and 1.1×10–3 (G
K) S·cm–2.Acetate (40mM) stimulated Na+ fluxes (8.5–9.9 Eq·cm–2·h–1) and Na-linked water fluxes (27–44 l·cm–2·h–1). Increased coupling ratios (2.9–4.6 l·Eq–1) and other data indicate that these effects may be due to increased osmotic permeabilities of barriers involved in the Na-linked water transfer pathway.Low-Na+ maintenance enhanced EPD (49–69 mV, serosa positive) and all net fluxes:J
Na (6.8–11.6);J
K (–3.2––4.3);J
Cl (4.3–5.6 Eq·cm serosal area–2·h–1);J
v (28–43 l·cm–2·h–1) (mucosal-serosal fluxes positive).Acute aldosterone enhancedJ
Na (10.8–14.0 Eq·cm–2·h–1) and EPD (54–66 mV) by 3 h after injection, but had no effect on the Na-linked components ofJ
K orJ
Cl.Abbreviations
ECPD, EPD
Electrochemical or electrical potential difference
-
G
Cl
,G
K
ionic conductances (Cl–, K+)
-
J
v
,J
ion
net volume or ion flux rate, mucosa-serosa positive;P
d
(Cl) diffusive permeability coefficient (of Cl–)
-
SEDM
standard error of difference between means 相似文献
6.
P. K. Lauf 《The Journal of membrane biology》1984,82(2):167-178
Summary Ouabain-resistant (OR), volume-or N-ethylmaleimide (NEM)-stimulated K+(Rb+)Cl– fluxes were measured in low-K+ sheep red cells and found to be functionally separate but immunologically similar. In anisosmotic solutions both K+ effluxes and Rb+ influxes of NEM-treated and control cells were additive. In contrast to the NEM-stimulated K+Cl– flux, metabolic depletion did not reduce K+Cl– flux of normal or swollen cells. The anion preference of OR K+ efflux in NEM-treated cells was Br–>Cl–>HCO
3
–
=F–I–=NO
3
–
=CNS–, and hence consistent with a reported Br–>Cl–>NO
3
–
sequence of the volume-dependent K+Cl– transport. Alloimmune anti-Ll antibodies known to decrease passive K+ fluxes in low K+ cells reduced by 51% both volume-and NEM-stimulated, furosemidesensitive Rb+Cl– fluxes suggesting their immunologic identity, a conclusion also supported by anti-L1 absorption studies. Since pretreatment with anti-L1 prevented the activation of Rb+ influx by NEM, and the impermeant glutathionmaleimide-I did not stimulate Rb+Cl– influx, the NEM reactive SH groups must be located apart from the L1 antigen either within the membrane or on its cytoplasmic face. A model is proposed consisting of a K+Cl– transport path(s) regulated by a protein with two functional subunits or domains; a chemically (C
s) and a volume (V
s)-stimulated domain, both interfacing with the L1 surface antigen. Attachment of alloanti-L1 from the outside reduces K+Cl– transport stimulated throughC
s by NEM orV
s by cell swelling. 相似文献
7.
Horst Onken Kai Graszynski 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1989,159(1):21-28
Summary Isolated posterior gills from Chinese crabs (Eriocheir sinensis) acclimated to tap-water were perfused and bathed with full, physiological saline (containing Na+ and Cl–). Under these conditions they developed an outside positive transepithelial potential difference (PDte). Substitution of Na+ by choline on both sides of the epithelium resulted in a substantial hyperpolarization of the PDte, while substitution of Cl– by gluconate reverses PDte to outside negative values.The magnitudes of the potential differences were strongly related to the adaptation media (artificial seawater or tap-water).The KCN-sensitive, outside positive PDte was shown to be strongly dependent on Cl–. Application of thiocyanate and 4-acetamido-4-isothiocyanato-stilbene-2,2 disulfonic acid (SITS) to the bath solution resulted in a reduction of the PDte, while the Cl–-channel blocker, diphenylamine-2-carboxylic acid (DPC), showed no effect. The PDte was markedly reduced by acetazolamide, an inhibitor of carbonic anhydrase (CA), and these results are discussed with reference to the presence of a Cl–/HCO
3
–
-exchanger in the apical membrane.Chloride was shown to pass the basolateral membrane via Cl–-channels: Diphenylamine-2-carboxylic acid (DPC) reduced the PDte with an IC50 of 3.7×10–5 mol/l when added to the perfusion saline. A basolateral K+-channel and its linkage to Cl– uptake could be demonstrated by using the K+-channel blocker, Ba2+, or increased K+ concentrations in the perfusion saline (PDte decrease). Ouabain did not reduce the PDte under nominally Na+-free conditions, indicating that the Cl– transport is independent of the Na+/K+-ATPase. In this paper we shall discuss the possible energy sources and linkages between pH regulation and active Cl– absorption under these experimental conditions.Abbreviations
A9C
anthracene-9-carboxylic acid
-
CA
carbonic anhydrase
-
DMSO
dimethylsulfoxide
-
DPC
diphenylamino-2-carboxylic acid
-
PD
te
transepithelial potential difference
-
SITS
4-acetamido-4-isothiocyanato-stilbene-2,2-disulfonic acid
-
TEA
tetraethyl-ammoniumchloride 相似文献
8.
Summary The requirement for Na+ and Cl– in the bathing media to obtain a maximal HCO
3
–
secretory flux (
) across isolated short-circuitedAmphiuma duodenum was investigated using titration techniques and ion substitution. Upon substitution of media Na+ with choline, HCO
3
–
secretion was markedly reduced. Replacement of media Cl– produced a smaller reduction of
. The presence of Cl– enhanced HCO
3
–
secretion only if Na+ was also in the media. Elevation of media Na+ or Cl– in the presence of the other ion produced a saturable increase of
. In the presence of Na+, Cl– stimulated
when added to the mucosal but not the serosal medium. In the presence of Cl–, Na+ elevated
when added to the serosal but not the mucosal medium. The ability of mucosal Cl– to stimulate
was not apparently dependent on mucosal Na+. Simultaneous addition of 10mm Cl– to the Na+-free mucosal medium and 10mm Na+ to the Cl–-free serosal medium stimulated
above levels produced by serosal Na+ alone. In conclusion, intestinal HCO
3
–
secretion required mucosal Cl– and serosal Na+ and did not involve mucosal NaCl cotransport. The results are consistent with a mucosal Cl– absorptive mechanism in series with parallel basolateral Na+–H+ and Cl––HCO
3
–
exchange mechanisms. 相似文献
9.
K. Nagashima M. Ando 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1994,164(1):47-54
To characterize mechanisms of esophageal desalination, osmotic water permeability and ion fluxes were measured in the isolated esophagus of the seawater eel. The osmotic permeability coefficient in the seawater eel esophagus was 2·10-4 cm·s-1. This value was much lower than those in tight epithelial, although the eel esophagus is a leaky epithelium with a tissue resistance of 77 ohm·cm-2. When the esophagus was bathed in normal Ringer solutions on both sides no net ion and water fluxes were observed. However, when mucosal NaCl concentration was increased by a factor of 3, Na+ und Cl- ions were transferred from mucosa to serosa (desalination). If only Na+ or Cl- concentration in the mucosal fluid was increased by a factor of 3, net Na+ and Cl- fluxes were reduced to 30–40%, indicating that 60–70% of the net Na+ and Cl- fluxes are coupled mutually. The coupled NaCl transport seems to be effective in desalting the luminal high NaCl. The remaining 30–40% of the total Na+ and Cl- fluxes seems to be due to a simple diffusion, because these components are independent of each other and follow their electrochemical gradients, and also because these fluxes remain even after treatment with NaCN or ouabain. A half of the coupled NaCl transport could be explained by a Na+/H+–Cl-/HCO
3
-
double exchanger on the apical membrane of the esophageal epithelium, because mucosal amiloride and 4.4-diisothiocyanatostilbene-2,2-disulphonic acid inhibited the net Na+ and Cl- fluxes by approximately 30%. The other half of the coupled NaCl transport, which follows their electrochemical gradients, still remains to be explained.Abbreviations DIDS
4,4-diisothiocyanatostilbene-2,2-disulphonic acid
- NMDG
N-methyl-d-glucosamine
-
P
Cl
Cl- permeability coefficient
- PD
transepithelial potential difference
-
P
Na
Na+ permeability coefficient
-
P
osm
osinotic permeability coefficient
- TALH
thick ascending limb of Henle's loop 相似文献
10.
The first analysis of chloride fluxes and compartmentation in a non-excised plant system is presented, examining ten ecologically pertinent conditions. The short-lived radiotracer couple 38Cl/39Cl was used as a Cl– tracer in intact barley (Hordeum vulgare L. cv. Klondike) seedlings, which were cultured and investigated under four external [Cl–], from abundant (0.1 mM) to potentially toxic (100 mM). Chloride–nitrogen interactions were investigated by varying N source (NO3
– or NH4
+) and strength (0.1 or 10 mM), in order to examine, at the subcellular compartmentation level, the antagonism, previously documented at the influx level, between Cl– and NO3
–, and the potential role of Cl– as a counterion for NH4
+ under conditions in which cytosolic [NH4
+] is excessive. Cytosolic [Cl–] increased with external [Cl–] from 6 mM to 360 mM. Cl– influx, fluxes to vacuole and shoot, and, in particular, efflux to the external medium, also increased along this gradient. Efflux reached 90% of influx at the highest external [Cl–]. Half-times of cytosolic Cl– exchange decreased between high-affinity and low-affinity influx conditions. The relationship between cytosolic [Cl–] and shoot flux indicated the presence of a saturable low-affinity transport system (SLATS) responsible for xylem loading of Cl–. N source strongly influenced Cl– flux to the vacuole, and moderately influenced Cl– influx and shoot flux, whereas efflux and half-time were insensitive to N source. Cytosolic pool sizes were not strongly or consistently influenced by N source, indicating the low potential for Cl– to act as a counterion to hyperaccumulating NH4
+. We discuss our results in relation to salinity responses in cereals.Abbreviations [Cl–]cyt
cytosolic chloride concentration
- [Cl–]o
external chloride concentration 相似文献
11.
Summary Loop diuretic-sensitive (Na+,K+,Cl–)-cotransport activity was found to be present in basolateral membrane vesicles of surface and crypt cells of rabbit distal colon epithelium. The presence of grandients of all three ions was essential for optimal transport activity (Na+,K+) gradien-driven36Cl fluxes weree half-maximally inhibited by 0.14 m bumetanide and 44 m furosimide. While86Rb uptake rates showed hyperbolic dependencies on Na+ and K+ concentrations with Hill coefficients of 0.8 and 0.9, respectively, uptakes were sigmoidally related to the Cl– concentration, Hill coefficient 1.8, indicating a 1 Na+: 1 K+:2 Cl– stoichiometry of ion transport.The interaction of putative (Na+, K+, Cl–)-cotransport proteins with loop diuretics was studied from equilibrium-binding experiments using [3H]-bumetanide. The requirement for the simulataneous presence of Na+,K+, and Cl–, saturability, reversibility, and specificity for diuretics suggest specific binding to the (Na+, K+, Cl–)-cotransporter. [3H]-bumetanide recognizes a minimum of two classes of diuretic receptors sites. high-affinity (K
D1=0.13 m;B
max1 =6.4 pmol/mg of protein) and low-affinity (K
D2=34 m;B
max2=153 pmol/mg of protein) sites. The specific binding to the high-affinity receptor was found to be linearly competitive with Cl– (K
1=60mm), whereas low-affinity sites seem to be unaffected by Cl–. We have shown that only high-affinity [3H]-bumetanide binding correlates with transport inhibition raising questions on the physiological significance of diuretic receptor site heterogeneity observed in rabbit distal colon epithelium. 相似文献
12.
Summary Ion dependence and electrogenicity of taurine uptake were studied in rabbit renal outer cortical brush-border membrane vesicles isolated by differential precipitation. Na+-d-glucose cotransport was followed in parallel to monitor changes in the membrane potential. Concentrative taurine flux was dependent on a chemical and/or an electrical Na+ gradient (K+ diffusion potential) and could be completely inhibited by other -amino acids. It displayed a specific anion requirement (Cl–Br–SCN–>I–>NO
3
–
). At chemical Na+ equilibrium, Cl– gradients, depending on their orientation, stimulated or inhibited taurine uptake more than could be attributed solely to electrical anion effects, although a Cl– gradient alone could not energize an overshoot. Furthermore, taurine tracer exchange was significantly stimulated by Cl– as well as Br–. The Cl– stoichiometry was found to be one, whereas taurine transport, in the presence of Cl–, was sigmoidally related to the Na+ concentration, resulting in a coupling ratio of 2 to 3 Na+: 1 taurine. Upon Cl– replacement with gluconate, taurine uptake showed a reduced potential sensitivity and was no longer detectably affected by the Na+ concentration (up to 150mm). These results suggest a 2 to 3 Na+:1 Cl–:1 taurine cotransport mechanism driven mainly by the Na+ gradient, which is sensitive to the membrane potential due to a negatively charged empty carrier. Cl– appears to stimulate taurine flux primarily by facilitating the formation of the translocated solute-carrier complex. 相似文献
13.
Peter Krippeit-Drews Gisela Drews Kai Graszynski 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1989,159(1):43-49
1. | Transepithelial potential differences (PDte) and acidification rates of the bath chamber were measured on isolated perfused posterior gills of the fiddler crabUca tangeri adapted to dilute seawater. |
2. | The PDte decreased to almost zero when Na+ was substituted by choline or when ouabain was added to the perfusion saline in high concentrations (10 mmol·l–1). Thus, the rheogenic NaCl-transport across the gill epithelium seems to be totally Na+-dependent. |
3. | When Cl– was replaced by gluconate, a bath positive PDte occurred which was insensitive to ouabain. This PDte could also be observed when, in addition to Cl– removal, Na+ was replaced by TMA+. |
4. | Bath acidification under normal conditions could be abolished by ouabain, indicating that there is H+ excretion via electrically silent Na+/H+ exchange. In contrast, bath acidification under Cl–-free conditions is only partially blocked by ouabain. |
5. | It is concluded that under Cl–-free conditions a rheogenic H+-pump in the apical membrane is responsible for the ouabain-insensitive bath acidification as well as for the PDte. |
14.
Giuliano Meyer Guido Bottà Carlo Rossetti Dario Cremaschi 《The Journal of membrane biology》1990,118(2):107-120
Summary In rabbit gallbladder epithelium, a Na+/H+, Cl–/HCO
3
–
double exchange and a Na+–Cl– symport are both present, but experiments on intact tissue cannot resolve whether the two transport systems operate simultaneously. Thus, isolated apical plasma membrane vesicles were prepared. After preloading with Na+, injection into a sodium-free medium caused a stable intravesicular acidification (monitored with the acridine orange fluorescence quenching method) that was reversed by Na+ addition to the external solution. Although to a lesser extent, acidification took place also in experiments with an electric potential difference (PD) equal to 0. If a preset pH difference (pH) was imposed ([H+]in>[H+]out, PD=0), the addition of Na-gluconate to the external solution caused pH dissipation at a rate that followed saturation kinetics. Amiloride (10–4
m) reduced the pH dissipation rate. Taken together, these data indicate the presence of Na+ and H+ conductances in addition to an amiloride-sensitive, electroneutral Na+/H+ exchange.An inwardly directed [Cl–] gradient (PD=0) did not induce intravesicular acidification. Therefore, in this preparation, there was no evidence for the presence of a Cl–/OH– exchange.When both [Na+] and [Cl–] gradients (outwardly directed, PD=0) were present, fluorescence quenching reached a maximum 20–30 sec after vesicle injection and then quickly decreased. The decrease was not observed in the presence of a [Na+] gradient alone or the same [Na+] gradient with Cl– at equal concentrations at both sides. Similarly, the decrease was abolished in the presence of both Na+ and Cl– concentration gradients and hydrochlorothiazide (5×10–4
m). The decrease was not influenced by an inhibitor of Cl–/OH– exchange (10–4
m furosemide) or of Na+–K+–2Cl– symport (10–5
m bumetanide).We conclude that a Na+/H+ exchange and a Na+–Cl– symport are present and act simultaneously. This suggests that in intact tissue the Na+–Cl– symport is also likely to work in parallel with the Na+/H+ exchange and does not represent an induced homeostatic reaction of the epithelium when Na+/H+ exchange is inhibited. 相似文献
15.
Examining the relationship between bacteria and heterotrophic nanoflagellates in Funka Bay (Japan) using the size-fractionation method 总被引:1,自引:0,他引:1
Choon Weng Lee Isao Kudo Hiroyasu Morishita Mitsuru Yanada Yoshiaki Maita 《Aquatic Ecology》2001,35(1):1-8
The chemical and biological conditions, and the bacteria-heterotrophic nanoflagellate (HNF) relationship were investigated in the vicinity of Funka Bay, southwest of Hokkaido, Japan during early spring 1999. At the time of sampling, chlorophyll a concentration, bacteria, phycoerythrin rich-cyanobacteria, and HNF abundance were in the following ranges: 0.3–3.6 g l–1, 2.5–5.6 × 105 cells ml–1, 0.6–1.2 × 103 cells ml–1, and 2.2–4.2 × 103 cells ml–1, respectively. Dissolved inorganic nitrogen, phosphate and silicate concentrations were in the ranges: 8.7–12.2 M, 0.9–2.0 M, and 21.6–25.5 M, respectively. Primary production ranged from 6.4 to 76.3 mg C m–3 d–1. Using water samples from regions of different productivity levels (in and outside bay), the bacteria - HNF relationship was uncoupled experimentally by the size-fractionation technique. Higher primary production (19.9 mg C m–3 d–1) in the bay supported higher bacterial growth rate (0.029 h–1). However, outside the bay both primary production (6.4 mg C m–3 d–1) and bacterial growth rate (0.007 h–1) were lower. The HNF growth rates and grazing rates were similar for both but by comparing both HNF grazing capacity and bacterial production, there was net decrease in bacterial abundance outside the bay and net increase inside the bay. The microbial parameters (rates and abundance) and the amount of carbon flow estimated through the phytoplankton – dissolved organic matter (DOM) – bacteria loop were different between the coastal station and the open ocean station. However HNF grazing and growth rates was similar for both stations. 相似文献
16.
Summary To assess the mechanism(s) by which intraluminal chloride concentration is raised above equilibrium values, intracellular Cl– activity (
i
Cl
) was studied in the proximal tubule ofNecturus kidney. Paired measurements of cell membrane PD (V
BL) and Cl-selective electrode PD (V
BL
Cl
) were performed in single tubules, during reversible shifts of peritubular or luminal fluid composition. Steadystate
i
Cl
was estimated at 14.6±0.6 mmol/liter, a figure substantially higher than that predicted for passive distribution. To determine the site of the uphill Cl– transport into the cell, an inhibitor of anion transport (SITS) was added to the perfusion fluid. Introduction of SITS in peritubular perfusate decreased
i
Cl
, whereas addition of the drug in luminal fluid slightly increased
i
Cl
; both results are consistent with basolateral membrane uphill Cl– transport from interstitium to the cell. TMA+ for Na+ substitutions in either luminal or peritubular perfusate had no effect on
i
Cl
. Removal of bicarbonate from peritubular fluid, at constant pH (a situation increasing HCO
3
–
outflux), resulted in an increase of
i
Cl
, presumably related to enhanced Cl– cell influx: we infer that Cl– is exchanged against HCO
3
–
at the basolateral membrane. The following mechanism is suggested to account for the rise in luminal Cl– concentration above equilibrium values: intracellular CO2 hydration gives rise to cell HCO
3
–
concentrations above equilibrium. The passive exit of HCO
3
–
at the basolateral membrane energizes an uphill entry of Cl– into the cell. The resulting increase of
i
Cl
, above equilibrium, generates downhill Cl– diffusion from cell to lumen. As a result, luminal Cl– concentration also increases.C.N.R.S. Greco 24. Part of this work was presented at the 12th annual meeting of the American Society of Nephrology, Boston, Mass. (Edelman et al., 1979). 相似文献
17.
Rapid lowering of the external pH (pH jump) enhances Cl– influx in Chara. Experiments were conducted to distinguish between two factors which have previously been proposed to mediate in the response: raised cytoplasmic pH and lowered cytoplasmic Cl– concentration. It is concluded that the latter alternative is more likely because: i) Cl– influx is reduced at high external pH; ii) influx following the pH jump is never greater than that following pretreatment in Cl–-free solution, which reduces cytoplasmic Cl– concentration (Cl– starvation); iii) the joint application of pH jump and Cl– starvation does not result in a greater Cl– influx than does Cl– starvation alone; and iv) addition of NH
4
+
, which increases cytoplasmic pH, does generate an additional stimulation of Cl– influx following a pH jump. It is suggested that the increased cytoplasmic pH at the end of pretreatment at high external pH decays rapidly during the pH jump, and thus any effect on Cl– influx is so transient as to be undetectable by the methods used. The results are discussed in terms of a reaction kinetic model for 2H+/Cl– cotransport (Sanders, D. and Hansen, U.-P, 1981, J. Member. Biol. 58, 139–153) which describes quantitatively; i) the effects of NH
4
+
on Cl– influx in terms involving only a change in cytoplasmic pH; and ii) the combined effects of Cl– starvation and NH
4
+
in terms involving only changes in Cl– concentration and cytoplasmic pH. Conversely, the combined effects of Cl– starvation and pH jump cannot be described by the model if the effect of the pH jump is the consequence of increased cytoplasmic pH. The simple interpretation of experiments on whole cells involving manipulation of
(the electrochemical potential difference for protons across the plasma membrane) is questioned in the light of these and previous findings that secondary factors can determine the response of Cl– transport in Chara.Abbreviations CPW
Chara pond water
- [Cl–]c
cytoplasmic Cl– concentration
- pHc
cytoplasmic pH
- pHo
external pH
-
transmembrane electrochemical gradient of protons
-
a membrane electrical potential difference 相似文献
18.
Summary The objectives of the 3 year study were to determine the relationship between bacterial numbers and phytoplankton standing crops (chlorophyll a) in sub-antarctic Marion Island lakes (33) and to determine the relative importance of labile dissolved organic carbon and water temperature as regulators of heterotrophic bacterial activity and production. Bacterial activity (the incorporation and respiration rates of 14C-labelled substrates) and production (the rate of [methyl-3H]thymidine incorporation into DNA) were measured in oligotrophic Lava Lake and Gentoo Lake, an elephant seal wallow. Samples were incubated under ambient conditions as well as at increased temperature and with additions of labile dissolved organic carbon (DOC). Bacterial numbers ranged from 2.13 × 105 cell ml–1 to 15.17 × 106 cells ml–1 in the lake survey. The chlorophyll range was 0.18 to >75 g 1–1. Bacterial numbers were not correlated to chlorophyll concentration in waters where the chlorophyll content was 5 g 1–1 but were correlated in waters with larger algal contents. Heterotrophic bacterial activity and production, which were similar to rates recorded for equivalent lower latitude systems, were higher in Gentoo Lake than in Lava Lake. As a result of qualitative and quantitative differences in the DOC pools, DOC was the stronger regulator of bacterial activity and production in Lava Lake, while temperature was the stronger factor in Gentoo Lake. 相似文献
19.
Dario Cremaschi Giuliano Meyer Carlo Rossetti Guido Bottà Paola Palestini 《The Journal of membrane biology》1987,95(3):209-218
Summary Cl– influx at the luminal border of the epithelium of rabbit gallbladder was measured by 45-sec exposures to36Cl– and3H-sucrose (as extracellular marker). Its paracellular component was evaluated by the use of 25mm SCN– which immediately and completely inhibits Cl– entry into the cell. Cellular influx was equal to 16.7eq cm–2 hr–1 and decreased to 8.5eq cm–2 hr–1 upon removal of HCO
3
–
from the bathing media and by bubbling 100% O2 for 45 min. When HCO
3
–
was present, cellular influx was again about halved by the action of 10–4
m acetazolamide, 10–5 to 10–4
m furosemide, 10–5 to 10–4
m 4-acetamido-4-isothiocyanostilbene-2,2-disulfonate (SITS), 10–3
m amiloride. The effects of furosemide and SITS were tested at different concentrations of the inhibitor and with different exposure times: they were maximal at the concentrations reported above and nonadditive. In turn, the effects of amiloride and SITS were not additive. Acetazolamide reached its maximal action after an exposure of about 2 min. When exogenous HCO
3
–
was absent, the residual cellular influx was insensitive to acetazolamide, furosemide and SITS. When exogenous HCO
3
–
was present in the salines, Na+ removal from the mucosal side caused a slow decline of cellular Cl– influx; conversely, it immediately abolished cellular Cl– influx in the absence of HCO
3
–
. In conclusion, about 50% of cellular influx is sensitive to HCO
3
–
, inhibitable by SCN–, acetazolamide, furosemide, SITS and amiloride and furthermore slowly dependent on Na+. The residual cellular influx is insensitive to bicarbonate, inhibitable by SCN–, resistant to acetazolamide, furosemide, SITS and amiloride, and immediately dependent on Na+. Thus, about 50% of apical membrane NaCl influx appears to result from a Na+/H+ and Cl–/HCO
3
–
exchange, whereas the residual influx seems to be due to Na+–Cl– contranport on a single carrier. Whether both components are simultaneously present or the latter represents a cellular homeostatic counterreaction to the inhibition of the former is not clear. 相似文献
20.
D. B. Shennan 《Bioscience reports》1995,15(4):231-239
Taurine transport by lactating gerbil mammary tissue has been examined. Taurine uptake is, mediated by a high-affinity system which is specific for -amino acids. The uptake of taurine is Na+-dependent but appears not to be obligatorly dependent upon Cl–. Thus, replacing Na+ with choline almost abolished taurine uptake. Substituting Cl– with NO
3
–
had no effect whereas SCN– induced a small but significant increase in taurine influx. Taurine uptake was Na+-dependent under conditions where Cl– had been replaced with NO
3
–
. However, it is apparent that the Na+-dependent taurine transport system requires the presence of a permeable anion because replacing Cl– with gluconate markedly reduced taurine uptake. Cell-swelling, induced by a hyposmotic challenge, increased the efflux of taurine from gerbil mammary tissue via a pathway sensitive to niflumic acid.Abbreviations Tris
(Tris(hydroxymethyl)aminomethane
- BES
(N,N-bis[2-hydroxyethyl]-2-aminoethane sulphonic acid) 相似文献