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1.
Effects of NaCl on ion relations and carbohydrate status of roots and on osmotic regulation of roots and shoots of Atriplex amnicola 总被引:2,自引:2,他引:0
Abstract Atriplex amnicola was grown at 25, 200 or 400 mol m3 NaCl. Root tissues at different stages of development were investigated for concentrations of K+, Na+ and Mg2+, and in some cases for Cl?. Sugar and starch concentrations were measured for plants grown at 25 or 400 mol m3 NaCl. In the ‘slightly vaeuolated’ root tips, Na+ was only 40 mol m?3 at an external concentration of 400 mol m?3 NaCl. The concentrations of K+ were not affected substantially by external NaCl between 25 mol m?3 and 400 mol m?3. The ‘highly vacuolated’ root tissues had substantially higher concentrations of K+, Na+ and Cl? in plants grown at 200 and 400 mol m 3 NaCl than in plants grown at 25 mol m?3 NaCl. Concentrations of Cr and of the sum of the cations in recently expanded tissue were similar to those in the bulk of the roots, consisting mainly of old cells. However, the K+: Na+ decreased with age; at 400 mol m?3 external NaCl with a K+: Na+ of 0.012, the K+: Na+ in recently expanded 12 mm root tips was as high as 1.6, compared with 0.7 for the bulk of the roots. These ion data were used to estimate cytoplasmic and vacuolar concentrations of K+ and Na +. Such calculations indicated that between 25 mol m3 and 400 mol m?3 external NaCl the concentration of the sum of (Na++K+) in the cytoplasm was maintained at about 180–200 mol m?3 (cell water basis). In contrast, the (Na++ K+) concentration in the vacuole was 170 mol m?3 for plants grown at 25 mol m?3 NaCl and 420 mol 400 mol m?3 NaCl. The expanding root (issues exhibited greatly decreased soluble sugars and starch between dusk and dawn. Ai both times, sugar and starch concentrations in these tissues were 2.5–4.0 times greater in plants grown at 400 mol m?3 NaCl compared with plants grown at 25 mol m?3 NaCl. In contrast, carbohydrate concentrations in expanded root tissues were very similar at 25 and 400 mol m?3 and showed little diurnal fluctuation. This paper considers the causes for the slower growth of A. amnicola at 400 than at 25 mol m”3 NaCl, using the data for the roots described here, and those for the shoots presented in the preceding paper (Aslam et al., 1986). There is no support for possible adverse effects by high internal ion concentrations. Instead, there may be deficiencies in supply of organic solutes for osmotic regulation; during part of the night a limited supply of such solutes may well restrict the rate of expansion of cells in plants growing at 400 mol m?3 NaCl. There is insufficient evidence to decide whether this limitation in the expanding tissues is particularly prominent for the roots or for the shoots. 相似文献
2.
The effect of temperature on viability of imbibed weed seeds 总被引:1,自引:0,他引:1
Imbibed seed of 10 common arable weeds were placed in trays in initially moist soil and, after imbibing for 2h, heated in ovens/incubators set to 31oC, 42oC, 56oC, 75oC or 100oC for 0.5, 1, 2, 4, 8 or 16 days or at 102oC, 155oC, 204oC or 262oC for 0.5, 1, 2, 5, 7.5 or 10 min. After heating, seeds were incubated for 28 days at 10/20oC or 20/30oC on a 12 h dark/light regime, depending on species, and germination recorded. At the lower temperatures, germination of all species was prevented by temperatures of 75oC or higher for periods of 0.5 days or more. Germination was lower after treatment at 56oC than at 31oC or 42oC for all species except Rumex obtusifolius. The maximum temperature required to prevent germination varied among species and was of greater importance than the duration of heating. Germination was variable with duration of heating. At the higher temperatures, there was very little germination of any species after heating at 204oC for 7.5 min or 262oC for 5 min or more. Seeds were greatly buffered from the air temperature by 3 mm of soil, throughout the shorter duration of heating. The average temperature of the soil, over the 10 min heating required to prevent over 90% germination, varied among species and ranged from 48oC for Avena fatua to 65oC for R. obtusifolius. This work implies that composting systems maintained at 65oC are unlikely to provide an efficient method of weed control. Recommendations for improvement of the laboratory technique are suggested. 相似文献
3.
The insoluble fraction of ox-brain, which had previously been shown to have a non-linear affinity for Na+ and K+, was prepared. Acetylcholine (1×10–8 mol/l and 1×10–7 mol/l) reduced the affinity of the fraction for Na+ and K+ to zero, while at 1×10–6 mol/l, the affinity for the cations was almost as high as in the absence of the transmitter; the affinities for Na+ and K+ were particularly high, when the supernatant concentrations of these ions exceeded 80–100 mM. Addition of eserine (3×10–5 mol/l) considerably modified the response of the fraction to acetylcholine (1×10–5 mol/l). Atropine (1×10–8 mol/l) in the absence or presence of acetylcholine (1×10–5, or 1×10–4 mol/l) reduced the affinity of the fraction for Na+ and K+ to zero. Epinephrine (3×10–10 mol/l) lowered the affinity for Na+ and K+, while ergotamine itself (1×10–5 mol/l) reduced it to zero. The addition of both epinephrine and ergotamine at the latter concentrations restored the affinity of the fractions for Na+ and K+ to what it had been in the absence of the transmitter or antagonist, previously reported. Norepinephrine (3×10–10 mol/l), or ouabain (1×10–7 mol/l) reduced the affinity of the fraction for Na+ and K+ to zero. Thus, the transmitters and antagonists altered the affinity of the insoluble fraction for Na+ and K+ nonlinearity, dependent upon their concentrations, the concentrations of the cations, and the interaction of transmitter and antagonist. 相似文献
4.
Vulkan R Yermiyahu U Mingelgrin U Rytwo G Kinraide TB 《The Journal of membrane biology》2004,202(2):97-104
Sorption of Cu2+ and Zn2+ to the plasma membrane (PM) of wheat root (Triticum aestivum Lcv. Scout 66) vesicles was measured at different pH values and in the presence of organic acids and other metals. The results were analyzed using a Gouy-Chapman-Stem model for competitive sorption (binding and electrostatic attraction) to a negative binding site. The binding constants for the two investigated cations as evaluated from the sorption experiments were 5 M–1 for Zn2+ and 400 M–1 for Cu2+. Thus, the sorption affinity of Cu2+ to the PM is considerably larger than that of Ca2+, Mg2+ or Zn2+. The greater binding affinity of Cu2+ was confirmed by experiments in which competition with La3+ for sorption sites was followed. The amount of sorbed Cu2+ decreased with increasing K+, Ca2+, or La3+ concentrations, suggesting that all these cations competed with Cu2+ for sorption at the PM binding sites, albeit with considerable differences among these cations in effectiveness as competitors with Cu2+. The sorption of Cu2+ and Zn2+ to the PM decreased in the presence of citric acid or malic acid. Citric acid (as well as pH) affected the sorption of Cu2+ or Zn2+ to PM more strongly then did malic acid. 相似文献
5.
- 1. (1) VO3− combines with high affinity to the Ca2+-ATPase and fully inhibits Ca2+-ATPase and Ca2+-phosphatase activities. Inhibition is associated with a parallel decrease in the steady-state level of the Ca2+-dependent phosphoenzyme.
- 2. (2) VO3− blocks hydrolysis of ATP at the catalytic site. The sites for VO3− also exhibit negative interactions in affinity with the regulatory sites for ATP of the Ca2+-ATPase.
- 3. (3) The sites for VO3− show positive interactions in affinity with sites for Mg2+ and K+. This accounts for the dependence on Mg2+ and K+ of the inhibition by VO3−. Although, with less effectiveness, Na+ substitutes for K+ whereas Li+ does not. The apparent affinities for Mg2+ and K+ for inhibition by VO3− seem to be less than those for activation of the Ca2+-ATPase.
- 4. (4) Inhibition by VO3− is independent of Ca2+ at concentrations up to 50 μM. Higher concentrations of Ca2+ lead to a progressive release of the inhibitory effect of VO3−.
Keywords: Ca2+-ATPase; Vanadate inhibition; K+; Li+; (Red cell membrane) 相似文献
6.
Anna BŁażewicz Grażyna Orlicz-Szczęsna Andrzej Prystupa Piotr Szczęsny 《Journal of trace elements in medicine and biology》2010,24(1):14-19
Ion chromatography followed by microwave-induced acid digestion was used to evaluate the serum levels of Fe3+, Cu2+, Ni2+, Zn2+, and Mn2+ in patients with diagnosed type 2 diabetes and in healthy controls. Recoveries ranged from 98.0% to 102% for Fe3+, from 89.9% to 100% for Cu2+, from 87.9% to 102% for Zn2+, and from 89.6% to 102% for Mn2+ were determined by examining samples spiked with various amounts of all the studied ions. The time of mineralization longer than 28 min did not affect the assay values. Precision was assessed at four unique concentrations in replicates of six, on four separate occasions. RSD was determined to be 1.16% for Fe3+, 5.20% for Cu2+, 2.8% for Zn2+, and 3.75% for Mn2+. The accuracy results (values of RSD) were as follows: 5.16% for Fe3+, 6.35% for Cu2+, 4.9% for Zn2+, and 7.23% for Mn2+.The statistical analysis confirmed that mean concentrations of Fe3+ and Zn2+ did not differ significantly from analogous values in the control group. Patients who additionally suffered from hypertension had higher copper concentrations compared with diabetic patients. For diabetics the presence of Mn2+ was not stated (LOD values amounting to 0.006 μg/mL). Ni2+ was not detectable for either the studied group or the control group (LOD=0.006 μg/mL). 相似文献
7.
Maize seeds and five-day-old maize seedlings were incubated in media containing Pb2+ at concentrations of 50, 100, and 200 mg 1-1 and Cd2+ at concentrations of 1, 5, 10 and 50 mg 1-1. After five days of incubation, both heavy metals were determined by means of AAS following wet mineralisation of roots and
shoots. The results obtained indicate that Pb2+ were transported to shoots from roots at a lower rate than Cd2+.
Phosphoenolpyruvate carboxylase (PEPC) isolated from germinating maize seeds was inhibited to a comparable degree by solutions
containing 0.001 mmol 1-1 Pb2+, 0.01 mmol 1-1 Cd2+, and 0.005 mmol 1-1 Cu2+. The enzyme was protected against this inhibition by the addition of mercaptoethanol, the substrate (PEP), or the cofactor
(Mg2+). The inhibition increased during a 20 min incubation of the enzyme with salts of the metals. Mn2+, Ni2+, and Co2+ ions could partially substitute for the metal cofactor Mg2+. Km values for these metal ions were as follows: for Mg2+ 0.07 mmol 1-1 in the range from 0 to 0.30 mmol 1-1 Mg2+; 0.71 mmol 1-1 for 0.30 to 2.50 mmol 1-1 Mg2+; for Mn2+ 0.36 mmol 1-1; for Ni2+ 0.34 mmol 1{-1}; and for Co2+ 0.20 mmol 1-1. The activity of the enzyme reached with Mn2+ 85 %, with Ni2+ 65 %, and with Co2+ 55 % of the activity recorded with Mg2+. 相似文献
8.
M Kurebe 《Life sciences》1979,24(3):275-281
The delipidated Ca++-ATPase prepared from intestinal brush border membranes showed a higher activity of Ca++-independent ATPase, a lower Km value for ATP and a higher Km value for Ca++ than its original membrane Ca++-ATPase. The addition of phosphatidylcholine re-activated the delipidated Ca++-ATPase to approximately 89 % of its original membrane Ca++-ATPase activity but did not restore the affinity for Ca++. This phospholipid raised the Km value for ATP but had little effect on the Km value for Ca++. Palmitic acid elevated the Km value for Ca++ but did not change the Km value for ATP. Kinetic analyses of these data suggest that the hydrocarbon chain of phosphatidylcholine is an important rate-limiting factor for the access of Ca++ to the enzyme and the polar head groups of phosphorylcholine and ester bond may be the factor for the access of ATP. 相似文献
9.
Results of energy calculations for α-MSH (α-melanocyte stimulating hormone, Ac-Ser1-Tyr2-Ser3-Met4-Glu5-His6-Phe7-Arg8-Trp9-Gly10-Lys11-Pro12-Val13-NH2) and [D -Phe7]α-MSH were used for design of cyclic peptides with the general aim to stabilize different conformational isomers of the parent compound. The minimal structural modifications of the conformationally flexible Gly10 residue, as substitutions for L -Ala, D -Ala, or Aib (replacing of hydrogen atoms by methyl groups), were applied to obtain octa- and heptapeptide analogues of α-MSH(4–11) and α-MSH(5–11), which were cyclized by lactam bridges between the side chains in positions 5 and 11. Some of these analogues, namely those with substitutions of the Gly10 residue with L -Ala or Aib, showed biological activity potencies on frog skin comparable to the potency of the parent tridecapeptide hormone. Additional energy calculations for designed cyclic analogues were used for further refinement of the model for the biologically active conformations of the His-Phe-Arg-Trp “message” sequence within the sequences of α-MSH and [D -Phe7]α-MSH. In such conformations the aromatic moieties of the side chains of the His6, L/D -Phe7, and Trp9 residues form a continuous hydrophobic “surface,” presumably interacting with a complementary receptor site. This feature is characteristic for low-energy conformers of active cyclic analogues, but it is absent in the case of inactive analogues. This particular spatial arrangement of functional groups involved in the message sequence is very close for α-MSH and [D -Phe7]α-MSH, as well as for biologically active cyclic analogues despite differences of dihedral angle values for corresponding low-energy conformations. © 1998 John Wiley & Sons, Inc. Biopoly 46: 155–167, 1998 相似文献
10.
The factors affecting the germination of spores of alkalophilic Bacillus species have been studied. The optimum pH for germination of spores of alkalophilic Bacillus No. 2b-2 was about 10 and NaCl (Na+) stimulated germination considerably. The optimum concentration of NaCl for germination was about 0.2 M. Other cations such as K+, NH4+, Rb + , Cs+ and Ca2+ did not stimulate germination. Li+ showed a weak activity for stimulating germination. Na+ ions stimulated the early step of germination. It was necessary for Na+ ions to co-exsist with the germinants in the germination of spores and the effect of Na+ was reversible. The same results were obtained for the germination of alkalophilic Bacillus No. 16-2 and No. 20. 相似文献
11.
Application of a multiplex PCR genotyping assay of 31 red blood cell antigens for establishment of a panel of reference DNA in China
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DNA based blood group genotyping has been widely used in clinical blood transfusions, and a number of different molecular blood group testing methods have been developed, including the detection of single nucleotide polymorphism (SNP) and genomic DNA sequencing. As the molecular bases of blood groups can differ widely between ethnic groups, a set of reference DNAs, especially for the Chinese population, is required for the development and validation of these methods, and for their optimal use in routine practice in China. In this study, a total of 100 DNA samples obtained from 60 established cell lines and 40 Chinese blood donors were typed for 31 red blood cell antigens of 13 blood group systems using a multiplex polymerase chain reaction (PCR) assay. Finally, nine DNA samples were selected to establish a panel of reference DNA that included M, N, S, s, Mur, Lua, Lub, Aua, Aub, K, k, Fya, Fyb, Jka, Jkb, Dia, Dib, Sc1, Sc2, Doa, Dob, Coa, Cob, Kna, Knb, Inb, Vel antigens and Fy (a-b-) null phenotype. 相似文献
12.
Synthetic cow urine labelled with 35S and 15N was applied to large, undisturbed, monolith lysimeters sampled from subsoiled and non-subsoiled areas of a grass/clover pasture. For one year following the urine application, the lysimeters were subjected to a combination of natural rainfall, simulated rainfall and simulated flood irrigations. Drainage from the lysimeters was sampled regularly and monthly (approx.) pasture cuts taken. At the end of the year, the lysimeters were destructively sampled in 50 mm depth increments for soil analysis. Leachates, plant samples and soil samples were analysed for 35S and 15N.There were no significant differences in plant uptake of 35S and 15N between the subsoiled and nonsubsoiled lysimeters. Initially grass showed a higher degree of labelling than clover. Total amounts of 35S and 15N leached from the subsoiled lysimeters were approximately twice that leached from the nonsubsoiled ones. Leaching patterns differed substantially between the two nutrients.Total recoveries of 35S (in plants, leachates and soil extracts) accounted for 82% of the applied 35S for the subsoiled lysimeters and 72% for non-subsoiled ones. The unrecovered 35S is considered to have been incorporated into soil organic matter. Total recoveries of 15N (in plants, soil and leachates) were similar to those for 35S, but unrecovered 15N is attributed to loss by denitrification. 相似文献
13.
W D McCubbin G E Willick C M Kay 《Biochemical and biophysical research communications》1973,50(3):926-933
The fluorescent analog of adenosine triphosphate (ATP)1 1,N6-ethenoadenosine triphosphate, (εATP), has been utilized as a substitute for ATP in the myosin and heavy meromyosin ATPase systems. For myosin, the analog εATP replaced ATP with a somewhat larger Km (2.6 × 10?4 mole ??1 for εATP as opposed to 8.8 × 10?5 mole ??1 for ATP), indicating that the apparent affinity of the enzyme for εATP is less than for ATP. Perhaps of more interest, further comparison yielded a Vmax for εATP about two and one half times the value for ATP (20 μmole PO4 sec?1 g protein?1 as opposed to 8.1 μmole sec?1 g protein?1). Results for the HMM-εATPase system were similar, yielding a Km value of 1.47 × 10?4 mole ??1 and a Vmax of 54.2 μmole PO4 sec?1 g protein?1, as opposed to corresponding Km and Vmax values of 1.23 × 10?4 mole ??1 and 20.4 μmole PO4 sec?1 g protein?1, respectively for the HMM-ATP interaction. The pH dependence of εATPase for both systems was comparable to ATP, suggesting a similarity in the mechanism of hydrolysis of the two nucleotides. Activation of εATPase by Ca2+ in the presence of 0.5 M KCl was comparable to ATPase for both systems, but inhibition by Mg2+ seemed to be more effective for εATPase. These results indicate that εATP is an excellent substitute for ATP in the myosin and heavy meromyosin systems and because of its insertion into the active site of these muscle proteins, it promises to be a very useful probe for conformation studies at this level. 相似文献
14.
Ulrich E. Grauer 《Plant and Soil》1993,157(2):319-331
There is good evidence for the ameliorating effect of SO4
2- and F- on the expression of Al phytotoxicity in acidic solutions. The role of OH-, in both shifting Al speciation towards hydroxy-Al species and decreasing activities of H+ with increasing pH, is still controversially discussed. Grauer and Horst (1992) proposed a model based on the assumption that Al phytotoxicity is a function of the Al saturation (AlS) of exchange sites in the root apoplast and analyzed the predictions of the model in the case of cation amelioration, with special emphasis on H+. In this study the model is further developed by considering, in addition to Al3+, the complexation of Al with the anions OH-, F-, SO4
2-, and Cl- to form potentially toxic Al species. Association constants of these Al complexes with a ligand (L
-) which is assumed to simulate the cation exchange sites in the root apoplast, were estimated. Affinity factors for binding to L
- compared to Al3+ were derived from these estimated association constants, and values were, in a first approach, 0.79 for AlOH2+, 0.02 for Al(OH)2
+, and 0.13 for Al(OH)3
0 (or 0.03 choosing another hydrolysis constant). High toxicity of Al13 (AlO4Al12(OH)24(H2O)12
7+) could be explained by diminished H+ amelioration and a high association constant to L
-. From estimated association constants for Al-Cl complexes, low affinity factors for L
- for these complexes were derived. Since the formation of these Al-Cl complexes is not favoured, Cl- is predicted to have very little ameliorating effect. In the case of SO4
2– and F- complexes with Al, the derived affinity factors never exceeded 0.05 and, since formation of these complexes is favoured by high association constants, are thus in agreement with experimental results on ameliorating effects. The ranking of the anions for ameliorative effectiveness was estimated to be in the order of OH->F->SO4
2–>Cl-. Hydroxy amelioration in this context is restricted to the speciation effect, which is only significant above pH 4. 相似文献
15.
K. P. Krishnan Christabelle E. G. Fernandes Sheryl Oliveira Fernandes P. A. Loka Bharathi 《Geomicrobiology journal》2013,30(1):31-36
Bacteria isolated from cobalt–enriched ferromanganese crusts on the Afanasiy Nikitin Seamounts in the Equatorial Indian Ocean were examined for their ability to tolerate, and immobilize cobalt in unamended seawater and seawater amended with 0.01% glucose. Retrievable bacterial counts in the form of CFU (colony forming units) on media supplemented with 1 mmol Co l?1 (58 mg Co l?1) and 1 mmol Mn l?1 (54 mg Mn l?1) were in the range of 1.71 × 104 to 1.05 × 105 gm?1 (wet wt) of crust, respectively. Most of the isolates (14/24) were pigmented and showed taxonomic affinities to Flavobacterium sp. Two representative isolates were tested for their tolerance of cobalt. We observed that in amended medium, the isolates tolerated up to 1 mmol Co l?1, whereas in unamended medium they tolerated upto 10 mmol Co l?1. Microscopic observations of cultures incubated with 10 mmol Co l?1 showed the occurrence of an extracellular slime layer, which may be responsible for immobilizing the cobalt from the liquid phase. In the unamended medium, the tolerance and stimulation in total cell counts was similar to that in amended medium or sometimes greater. Total cell counts peaked at 100 μmol Co l?1 for incubations in unamended medium (1.1–2.5 × 1011 cells l?1) and at 0.1–1 μmol Co l?1 for incubations in amended medium (1.5–2.6 × 1011 cells l?1). Counts of formazan-stained respiring cells of both the isolates in the unamended medium reached up to a maximum of 2.9–7.8 × 1010 l?1 after incubation for 10 days at 23(±1)°. In the amended medium cell counts of respiring cells attained a maximum in the range of 4.6–15.8 × 1010 l?1 at 100 μmol Co l?1. The Co immobilization rate was on average 82 (± 87.9, n = 24) μmol of Co d?1. Since the isolates were naturally occurring bacteria from crusts, they could be more environmentally acceptable and safe if used for metal recovery and bio-leaching. 相似文献
16.
Summary Cl– influx into cells ofChara corallina is shown to be stimulated by a factor of 2 to 4 by starvation of Cl–. The time constant for the induction of this effect is about 4.0 ksec and that for its decay when Cl– is reprovided, 1.7 ksec. Intracellular perfusion of tonoplast-free cells with solutions of varying Cl– concentration shows that Cl– influx can be controlled directly by the concentration of Cl– at the inside of the plasma membrane. Both the time course for the initial stages of induction of the starvation-stimulated flux and its absolute magnitude can be accounted for by assuming cytoplasmic Cl– concentration to be the only intracellular condition to change during Cl– starvation. The existence of a feedback loop between cytoplasmic Cl– and Cl– influx provides an alternative explanation to observations previously used in support of a Cl–/OH– exchange hypothesis (F.A. Smith, 1972,New Phytol.
71:595). 相似文献
17.
Joesph R. Wiencek Jamila Hirbawi Vivien C. Yee Michael Kalafatis 《The Journal of biological chemistry》2016,291(4):1565-1581
Prothrombin (FII) is activated to α-thrombin (IIa) by prothrombinase. Prothrombinase is composed of a catalytic subunit, factor Xa (fXa), and a regulatory subunit, factor Va (fVa), assembled on a membrane surface in the presence of divalent metal ions. We constructed, expressed, and purified several mutated recombinant FII (rFII) molecules within the previously determined fVa-dependent binding site for fXa (amino acid region 473–487 of FII). rFII molecules bearing overlapping deletions within this significant region first established the minimal stretch of amino acids required for the fVa-dependent recognition exosite for fXa in prothrombinase within the amino acid sequence Ser478–Val479–Leu480–Gln481–Val482. Single, double, and triple point mutations within this stretch of rFII allowed for the identification of Leu480 and Gln481 as the two essential amino acids responsible for the enhanced activation of FII by prothrombinase. Unanticipated results demonstrated that although recombinant wild type α-thrombin and rIIaS478A were able to induce clotting and activate factor V and factor VIII with rates similar to the plasma-derived molecule, rIIaSLQ→AAA with mutations S478A/L480A/Q481A was deficient in clotting activity and unable to efficiently activate the pro-cofactors. This molecule was also impaired in protein C activation. Similar results were obtained with rIIaΔSLQ (where rIIaΔSLQ is recombinant human α-thrombin with amino acids Ser478/Leu480/Gln481 deleted). These data provide new evidence demonstrating that amino acid sequence Leu480–Gln481: 1) is crucial for proper recognition of the fVa-dependent site(s) for fXa within prothrombinase on FII, required for efficient initial cleavage of FII at Arg320; and 2) is compulsory for appropriate tethering of fV, fVIII, and protein C required for their timely activation by IIa. 相似文献
18.
Zerella MJ Stiffler DF 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1999,169(7):481-486
We measured Ca2+ exchanges across the skin of larval and adult Ambystoma tigrinum using the radio-isotope influx method. We found that the skin of both morphs takes up Ca2+ in a manner that is proportional to external [Ca2+], saturable and oriented against the electrochemical gradient for Ca2+. We conclude that this uptake occurs by active transport. Kinetic analysis yields affinities for calcium ions that are similar
to the affinities for both Ca2+ and Na+ in the skin of other amphibians. The capacity for calcium is similar to Ca2+ capacity in other amphibians. The capacity for Ca2+ is lower than the capacity for Na+. Cutaneous Ca2+ deposits are lower in this urodele than found in anurans. Adults tend to have higher levels of Ca in their skin than do larvae.
Accepted: 25 June 1999 相似文献
19.
Voltage-gated Ca2+ channels (VGCCs) are recognized for their superb ability for the preferred passage of Ca2+ over any other more abundant cation present in the physiological saline. Most of our knowledge about the mechanisms of selective Ca2+ permeation through VGCCs was derived from the studies on native and recombinant L-type representatives. However, the specifics of the selectivity and permeation of known recombinant T-type Ca2+-channel α1 subunits, Cav3.1, Cav3.2 and Cav3.3, are still poorly defined. In the present study we provide comparative analysis of the selectivity and permeation Cav3.1, Cav3.2, and Cav3.3 functionally expressed in Xenopus oocytes. Our data show that all Cav3 channels select Ca2+ over Na+ by affinity. Cav3.1 and Cav3.2 discriminate Ca2+, Sr2+ and Ba2+ based on the ion's effects on the open channel probability, whilst Cav3.3 discriminates based on the ion's intrapore binding affinity. All Cav3s were characterized by much smaller difference in the KD values for Na+ current blockade by Ca2+ (KD1 ∼ 6 μM) and for Ca2+ current saturation (KD2 ∼ 2 mM) as compared to L-type channels. This enabled them to carry notable mixed Na+/Ca2+ current at close to physiological Ca2+ concentrations, which was the strongest for Cav3.3, smaller for Cav3.2 and the smallest for Cav3.1. In addition to intrapore Ca2+ binding site(s) Cav3.2, but not Cav3.1 and Cav3.3, is likely to possess an extracellular Ca2+ binding site that controls channel permeation. Our results provide novel functional tests for identifying subunits responsible for T-type Ca2+ current in native cells. 相似文献
20.
The Na+/H+ antiporter NhaA is the main Na+ extrusion system in E. coli. Using direct current measurements combined with a solid supported membrane (SSM), we obtained electrical data of the function of NhaA purified and reconstituted in liposomes. These measurements demonstrate NhaA's electrogenicity, its specificity for Li+ and Na+ and its pronounced pH dependence in the range pH 6.5-8.5. The mutant G338S, in contrast, presents a pH independent profile, as reported previously. A complete right-side-out orientation of the NhaA antiporter within the proteoliposomal membrane was determined using a NhaA-specific antibody based ELISA assay. This allowed for the first time the investigation of NhaA in the passive downhill uptake mode corresponding to the transport of Na+ from the periplasmic to the cytoplasmic side of the membrane. In this mode, the transporter has kinetic properties differing significantly from those of the previously investigated efflux mode. The apparent Km values were 11 mM for Na+ and 7.3 mM for Li+ at basic pH and 180 mM for Na+ and 50 mM for Li+ at neutral pH. The data demonstrate that in the passive downhill uptake mode pH regulation of the carrier affects both apparent Km as well as turnover (Vmax). 相似文献