共查询到20条相似文献,搜索用时 31 毫秒
1.
M.M. Hammoudah S. Nir T. Isac R. Kornhauser T.P. Stewart S.W. Hui W.L.C. Vaz 《生物化学与生物物理学报:生物膜》1979,558(3)
The interaction of La3+ with phosphatidylserine vesicles is elucidated by binding studies, differential scanning calorimetry, X-ray diffraction, freeze fracture electron microscopy, and release of vesicle contents. La3+ effectively competes with Ca2+ for phosphatidylserine binding sites. The saturation level is close to a La/lipid ratio of 1:3. A concentration of 0.1 mM of La3+ is sufficient to induce fusion between sonicated vesicles. 相似文献
2.
M.M Hammoudah S Nir J Bentz E Mayhew T.P Stewart S.W Hui R.J Kurland 《生物化学与生物物理学报:生物膜》1981,645(1):102-114
The interaction of La3+ with phosphatidylserine vesicles is studied by differential scanning calorimetry, 140La binding, 31P-NMR chemical shifts and relaxation rates, carboxyfluorescein and [14C]sucrose release, X-ray diffraction and freeze-fracture electron microscopy. In the presence of La3+ concentrations above 1 mM and an incubation temperature of 38°C, i.e., at the phase transition temperature of the complex La/phosphatidylserine, the binding ratio of La/lipid exceeds a ratio, reaching saturation at a ratio. Analysis, employing a modified Gouy-Chapman equation, indicates a significant increase in the intrinsic binding constant of La/phosphatidylserine when the La3+ concentration exceeds the threshold concentration for leakage. The analysis illustrates that at the molecular level the binding of La3+ can be comparable to or even weaker than that of Ca2+, but that even when present at smaller concentrations La3+ competes with and partially displaces Ca2+ from membranes or other negatively charged surfaces. The results suggest that the sequence La3+>Ca2+>Mg2+ reflects both the binding strength of these cations to phosphatidylserine as well as their ability to induce leakage, enhancement of 31P spin-lattice relaxation rates, fusion and other structural changes. The leakage, fusion, and other structural changes are more pronounced at the phase transition temperature of the La/lipid complex. 相似文献
3.
The effects of phospholipid vesicles and divalent cations in the subphase solution on the surface tension of phospholipid monolayer membranes were studied in order to elucidate the nature of the divalent cation-induced vesicle-membrane interaction. The monolayers were formed at the air/water interface. Various concentrations of unilamellar phospholipid (phosphatidylserine, phosphatidylcholine and their mixtures) vesicles and divalent cations (Mg2+, Ca2+, Mn2+, etc.) were introduced into the subphase solution of the monolayers. The changes of surface tension of monolayers were measured by the Wilhelmy plate (Teflon) method with respect to divalent ion concentrations and time.When a monolayer of phosphatidylserine and vesicles of phosphatidylserine/phosphatidylcholine (1 : 1) were used, there were critical concentrations of divalent cations to produce a large reduction in surface tension of the monolayer. These concentrations were 16 mM for Mg2+, 7 mM for Sr2+, 6 mM for Ca2+, 3.5 mM for Ba2+ and 1.8 mM for Mn2+. On the other hand, for a phosphatidylcholine monolayer and phosphatidylcholine vesicles, there was no change in surface tension of the monolayer up to 25 mM of any divalent ion used. When a phosphatidylserine monolayer and phosphatidylcholine vesicles were used, the order of divalent ions to effect the large reduction of surface tension was Mn2+ > Ca2+ > Mg2+ and their critical concentrations were in between the former two cases. The threshold concentrations also depended upon vesicle concentrations as well as the area/molecule of monolayers. For phosphatidylserine monolayers and phosphatidylserine/phosphatidylcholine (1 : 1) vesicles, above the critical concentrations of Mn2+ and Ca2+, the surface tension decreased to a value close to the equilibrium pressure of the monolayers within 0.5 h.This decrease in surface tension of the monolayers is interpreted partly as the consequence of fusion of the vesicles with the monolayer membranes. The 相似文献
4.
Small unilamellar phosphatidylserine/phosphatidylcholine liposomes incubated on one side of planar phosphatidylserine bilayer membranes induced fluctuations and a sharp increase in the membrane conductance when the Ca2+ concentration was increased to a threshold of 3–5 mM in 100 mM NaCl, pH 7.4. Under the same ionic conditions, these liposomes fused with large (0.2 μm diameter) single-bilayer phosphatidylserine vesicles, as shown by a fluorescence assay for the mixing of internal aqueous contents of the two vesicle populations. The conductance behavior of the planar membranes was interpreted to be a consequence of the structural rearrangement of phospholipids during individual fusion events and the incorporation of domains of phosphatidylcholine into the Ca2+-complexed phosphatidylserine membrane. The small vesicles did not aggregate or fuse with one another at these Ca2+ concentrations, but fused preferentially with the phosphatidylserine membrane, analogous to simple exocytosis in biological membranes. Phosphatidylserine vesicles containing gramicidin A as a probe interacted with the planar membranes upon raising the Ca2+ concentration from 0.9 to 1.2 mM, as detected by an abrupt increase in the membrane conductance. In parallel experiments, these vesicles were shown to fuse with the large phosphatidylserine liposomes at the same Ca2+ concentration. 相似文献
5.
Mn2+ binding to vesicles prepared from several different species of anionic phospholipids was determined as a function of temperature by electron paramagnetic resonance (EPR). The Mn2+ affinities of phosphatidylserine, cardiolipin and egg yolk phosphatidylglycerol all increased monitonically with temperature.Vesicles prepared from hydrogenated and natural (bovine) phosphatidylserine were monitored with respect to hydrocarbon chain fluidity as well as Mn2+ binding. Contrary to expectations based on surface potential considerations, the affinity of phosphatidylserine for divalent cations was apparently not lowered in going from the gel state to the liquid crystalline state of the bilayer. The results are instead consistent with an enhancement in cation affinity with increased lipid fluidity.Dipalmitoyl phosphatidylglycerol vesicle fluidity and Mn2+ binding were also studied with EPR. A large reduction in the measured Mn2+ affinity accompanied melting of the phospholipid, but observed hysteresis in the temperature dependence of the binding render uncertain any simple explanation based on changes in surface potential. Supplementary light scattering data indicated that vesicle aggregation was involved in the hysteresis phenomena. 相似文献
6.
Dynamic light scattering has been used to study the temperature dependence of Ca2+-induced fusion of phosphatidylserine vesicles and mixed vesicles containing phosphatidylserine and different phosphatidylcholines. The final vesicle size after Ca2+ and EDTA incubation serves as a measure of the extent of fusion. With phosphatidylserine vesicles, the extent of fusion shows a sharp maximum at an incubation temperature which depends on the Ca2+ concentration between 0.8 and 2 mM. The shift in the fusion peak temperature with Ca2+ concentration is similar to the typical shift in the phase transition temperature with divalent cation concentration in acidic phospholipids. The results suggest a direct correlation between the fusion peak temperature and the phase transition temperature in the presence of Ca2+ prior to fusion. With mixed vesicles containing up to 33% of a phosphatidylcholine in at least 2 mM Ca2+, the extent of fusion as a function of incubation temperature also shows a maximum. The fusion peak temperature is essentially independent of the quantity and type of phosphatidylcholine and the Ca2+ concentration, and identical to that with pure phosphatidylserine in excess Ca2+. The results imply that Ca2+-induced molecular segregation occurs first, and fusion subsequently takes place between pure phosphatidylserine domains. 相似文献
7.
The binding of glutamate decarboxylase (GAD), to phospholipid vesicles (liposomes) in the absence and in the presence of several Ca2+ and Mg2+ concentrations was studied. Phosphatidylcho-line-phosphatidylserine (4:1) liposomes are capable of binding GAD in a Ca2+-dependent manner. The per cent of GAD bound increased from 5 to 65°., in a sigmoid shape with Ca2+ concentrations in the 0.2-4 mm range. Mg2+ also induces GAD binding but is less effective than Ca2+ The Ca2+ -dependent binding of GAD is not the result of unspecific association of protein, since Ca2+ did not promote any binding of choline acetyltransferase or lactate dehydrogenase. Furthermore, the relative specific activity (oo enzyme activity/% protein) of GAD associated to liposomes increases 4-fold from 0 to 2 mm Ca2+. The per cent of GAD bound attains a plateau at a ratio phospholipid/protein of about 1.5. and decreases when the pH increases from 6.5 or 6.8 to 7 or 7.25. Na+ or K+ at a 100mm concentration also induce binding of GAD to liposomes. Phosphatidylcholine liposomes (without phosphatidylserine) practically did not bind GAD at any Ca2+ concentration. The Ca2+-dependent association of GAD to phosphatidylcholine-phosphatidylserine liposomes is very similar to that previously reported using brain membranes, and it correlates also well with the reported Ca2+-dependent aggregation of phosphatidylserine molecules in phospholipid membranes of similar composition. It is concluded that phosphatidylserine is probably involved in the Ca2+-dependent binding of GAD to brain membranes. Phospholipid vesicles seem to be a useful experimental model for studying the mechanisms of this GAD association to membranes and the possible physiological implications of the GAD-Ca2+-membrane interaction regarding the release of newly synthesized GABA from nerve endings. 相似文献
8.
Nejat Düzgünes Jan Wilschut Robert Fraley Demetrios Papahadjopoulos 《生物化学与生物物理学报:生物膜》1981,642(1):182-195
We have investigated the contribution of various phospholipids to membrane fusion induced by divalent cations. Fusion was followed by means of a new fluorescence assay monitoring the mixing of internal aqueous contents of large (0.1 μm diameter) unilamellar liposomes. The rate and extent of fusion induced by Ca2+ in mixed phosphatidylserine/phosphatidylcholine vesicles were lower compared to those in pure phosphatidylserine vesicles. The presence of 50% phosphatidylcholine completely inhibited fusion, although the vesicles aggregated upon Ca2+ addition. When phosphatidylserine was mixed with phosphatidylethanolamine, however, rapid fusion could be induced by Ca2+ even in mixtures that contained only 25% phosphatidylserine. Phosphatidylethanolamine also facilitated fusion by Mg2+ which could not fuse pure phosphatidylserine vesicles. In phosphatidylserine/phosphatidylethanolamine/phosphatidylcholine mixtures, in which the phosphatidylcholine content was kept at 25%, phosphatidylethanolamine could not substitute for phosphatidylserine, and the fusogenic capacity of Mg2+ was abolished by the presence of merely 10% phosphatidylcholine. The initial rate of release of vesicle contents was slower than the rate of fusion in all the mixtures used. The presence of phosphate effected a considerable decrease in the threshold concentration of Ca2+ and also enhanced 相似文献
9.
D. Papahadjopoulos W.J. Vail C. Newton S. Nir K. Jacobson G. Poste R. Lazo 《生物化学与生物物理学报:生物膜》1977,465(3):579-598
The interaction of phosphatidylserine vesicles with Ca2+ and Mg2+ has been examined by several techniques to study the mechanism of membrane fusion. Data are presented on the effects of Ca2+ and Mg2+ on vesicle permeability, thermotropic phase transitions and morphology determined by differential scanning calorimetry, X-ray diffraction, and freeze-fracture electron microscopy. These data are discussed in relation to information concerning Ca2+ binding, charge neutralization, molecular packing, vesicle aggregation, phase transitions, phase separations and vesicle fusion.The results indicate that at Ca2+ concentrations of 1.0–2.0 mM, a highly cooperative phenomenon occurs which results in increased vesicle permeability, aggregation and fusion of the vesicles. Under these conditions the hydrocarbon chains of the lipid bilayers undergo a phase change from a fluid to a crystalline state. The aggregation of vesicles that is observed during fusion is not sufficient in itself to induce fusion without a concomitant phase change. Mg2+ in the range of 2.0–5.0 mM induces aggregation of phosphatidylserine vesicles but no significant fusion nor a phase change.From the effect of variations in pH, temperature, Ca2+ and Mg2+ concentration on the fusion of vesicles, it is concluded that the key event leading to vesicle membrane fusion is the isothermic phase change induced by the bivalent metals. It is proposed that this phase change induces a transient destabilization of the bilayer membranes that become susceptible to fusion at domain boundaries. 相似文献
10.
Robert Kurland Carolyn Newton Shlomo Nir Demetrios Papahadjopoulos 《生物化学与生物物理学报:生物膜》1979,551(1):137-147
23Na NMR relaxation rate measurements show that Na+ binds specificially to phosphatidylserine vesicles and is displaced partially from the binding site by K+ and Ca2+ but to a considerably less extent by tetraethylammonium ion. The data indicate that tetraethylammonium ion affects the binding of Na+ only slightly, by affecting the surface potential through its presence in the double layer, without competing for a phosphatidylserine binding site. Values for the intrinsic binding constant for the Na+-phosphatidylserine complex that would be consistent with the competition experiments (and the dependence of the relaxation rate on concentration of free Na+) fall in the range 0.4–1.2 M?1 with a better fit towards the higher values. We conclude that in the absence of competing cations in solution an appreciable fraction of the phosphatidylserine sites could be associated with bound Na+ at 0.1 M Na+ concentration. 相似文献
11.
Cathy L. Selvius DeRoo Charles F. Yocum 《Biochemical and biophysical research communications》1981,100(3):1025-1031
Ferricyanide-supported oxygen evolution in sonic vesicles from the cyanobacterium is only partially sensitive to inhibition by 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone (DBMIB), and addition of cations to inhibited membranes stimulates the rate of oxygen evolution. The order of cation effectiveness (M3+ > M2+ > M+) suggests that this stimulation is due at least in part to surface charge screening effects which permit freer access of anionic ferricyanide to the vesicle membrane surface; La3+, Ca2+, and K+ are most effective in this regard. Ferricyanide photoreduction is completely sensitive to 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU), and neither mono- nor divalent cations affect this inhibition. Addition of La3+, on the other hand, causes a nearly complete restoration of ferricyanide-supported oxygen evolution. We conclude that the membrane surfaces of these vesicles are uniquely different from those o higher plants; sites of ferricyanide reduction associated with the interphotosystem chain are surface localized, and the primary acceptor region of photosystem II is susceptible to a trivalent cation-specific reaction in which ferricyanide may directly oxidize the primary acceptor. 相似文献
12.
The interaction of La 3+ with mitochondria in relation to respiration-coupled Ca 2+ transport 总被引:9,自引:0,他引:9
La3+ inhibits the respiration-dependent accumulation of Ca2+ by rat liver mitochondria when added in very small amounts (0.1–l.0 nmole per mg protein). However, La3+ itself does not activate respiration. With the use of 140La3+ it was found that La3+ is very rapidly bound to rat liver mitochondria in a respiration-independent process accompanied by loss of H+ to the medium. When both La3+ and Ca2+ are added to mitochondria simultaneously, most of the La3+ but little Ca2+ are bound. La3+ added to mitochondria previously loaded with Ca2+ is tightly bound without discharge of Ca2+. Conversely, when Ca2+ is added to La3+-loaded mitochondria it is not bound nor is the La3+ discharged. La3+ inhibits both high-affinity and low-affinity respiration-independent Ca2+ binding. Isotopic experiments showed that La3+ is, in fact, bound to the same high-affinity sites as Ca2+, in both intact mitochondria and in mitochondrial extracts. It is concluded (1) that La3+ binds to and inhibits the Ca2+ carrier; (2) that La3+ is not transported by the Ca2+ carrier; and (3) that La3+ is, in addition, bound to a large number of external sites on mitochondria for which Ca2+ is not a strong competitor. 相似文献
13.
稀土La3+跨PC12细胞膜行为研究 总被引:1,自引:0,他引:1
使用AR-CM-M1C阳离子测定系统,发展Fura-2荧光测定技术,将其应用于测定细胞内游离稀土离子La3+,并以此研究了La3+跨PC12细胞(大鼠嗜铬细胞瘤细胞)膜的行为.结果表明:在模拟细胞内离子组分,pH=7.05的溶液中,测得La3+-Fura-2的表观解离常数为3.27×10-11 mol·L-1.对于PC12细胞,静息条件下La3+不能跨越细胞膜进入胞内.与钙离子通道相关的KCl和去甲肾上腺素均不能刺激稀土La3+过膜.用哇巴因(ouabain)使胞内Na+超载后,La3+可过膜进入细胞内,且过膜量与胞外La3+浓度和胞内Na+超载程度有一定的浓度依赖关系,提示La3+可以经由Na+/La3+交换机制过膜而进入细胞内. 相似文献
14.
Pérez-Lara A Corbalán-García S Gómez-Fernández JC 《Archives of biochemistry and biophysics》2011,(1):36-41
Curcumin modulates the activity of protein kinase Cα (PKCα) when assayed in the presence of vesicles including phosphatidylcholine, phosphatidylserine and diacylglycerol. Increasing concentrations of curcumin progressively increased PKCα activity at concentrations lower than 20 μM, but at higher concentrations of curcumin the activity decreased although, at concentrations of curcumin of up to 100 μM the activity was always higher than the basal one (in the absence of curcumin). The maximum activity was reached at 3 μM curcumin, at 20 and 30 mol% of phosphatidylserine, 10 μM Ca2+ and 2 mol% diacylglycerol. The same type of modulation was observed when changing the concentration of phosphatidylserine, diacylglycerol and Ca2+. No effect of curcumin was found when the activity was assayed in the presence of Triton X-100 mixed micelles which included phosphatidylserine and diacylglycerol, indicating that the effect of curcumin was membrane-dependent. The pattern of binding of PKCα to membrane vesicles as a function of curcumin concentration closely correlated with the pattern of activating effect. It was concluded that the effect of curcumin on PKCα activity was related to its effect on the membrane, which may modulate the binding of the enzyme to the membrane. 相似文献
15.
Interactive effects of Al, h, and other cations on root elongation considered in terms of cell-surface electrical potential 总被引:3,自引:0,他引:3
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The rhizotoxicities of Al3+ and of La3+ to wheat (Triticum aestivum L.) were similarly ameliorated by cations in the following order of effectiveness: H+ ≈ C3+ > C2+ > C1+. Among tested cations of a given charge, ameliorative effectiveness was similar except that Ca2+ was slightly more effective than other divalent cations and H+ was much more effective than other monovalent cations. H+ rhizotoxicity was also ameliorated by cations in the order C3+ > C2+ > C1+. These results suggest a role for cell-surface electrical potential in the rhizotoxicity of Al3+, La3+, H+, and other toxic cations: negatively charged cell surfaces of the root accumulate the toxic cations, and amelioration is effected by treatments that reduce the negativity of the cell-surface electrical potential by charge screening or cation binding. Membrane-surface activities of free Al3+ or La3+ computed according to a Gouy-Chapman-Stern model correlated well with growth inhibition, which correlated only poorly with Al3+ or La3+ activities in the external medium. The similar responses of Al-intoxicated and La-intoxicated roots to ameliorative treatments provide evidence that Al3+, rather than AlOH2+ or Al(OH)2+, is the principal toxic species of mononuclear Al. Comparisons of the responses of Al-sensitive and Al-tolerant wheats to Al3+ and to La3+ did not support the hypothesis that varietal sensitivity to Al3+ is based upon differences in cell-surface electrical potential. 相似文献
16.
U. Yermiyahu G. Rytwo D.K. Brauer T.B. Kinraide 《The Journal of membrane biology》1997,159(3):239-252
A general model for the sorption of trivalent cations to wheat-root (Triticum aestivum L cv. Scout 66) plasma membranes (PM) has been developed and includes the first published coefficients for La3+ and Al3+ binding to a biological membrane. Both ions are rhizotoxic, and the latter ion is the principal contributor to the toxicity
of acidic soils around the world. The model takes into account both the electrostatic attraction and the binding of cations
to the negatively charged PM surface. Ion binding is modeled as the reaction P
−+I
Z⇌PI
Z
−1 in which P
− represents a negatively charged PM ligand, located in an estimated area of 540 ?2, and I
Z represents an ion of charge Z. Binding constants for the reaction were assigned for K+ (1 m
−1) and Ca2+ (30 m
−1) and evaluated experimentally for La3+ (2200 m
−1) and H+ (21,500 m
−1). Al sorption is complicated by Al3+ hydrolysis that yields hydroxoaluminum species that are also sorbed. Binding constants of 30 and 1 m
−1 were assigned for AlOH2+ and Al(OH)+
2, respectively, then a constant for Al3+ (20,000 m
−1) was evaluated experimentally using the previously obtained values for K+, Ca2+ and H+ binding. Electrostatic attraction was modeled according to Gouy-Chapman theory. Evaluation of parameters was based upon the
sorption of ions to PM vesicles suspended in solutions containing variable concentrations of H+, Ca2+ and La3+ or Al3+. Use of small volumes, and improved assay techniques, allowed the measurement of concentration depletions caused by sorption
to vesicles. Some independent confirmation of our model is provided by substantial agreement between our computations and
two published reports of La3+ effects upon zeta potentials of plant protoplasts. The single published report concerning the electrostatic effects of Al
on cell membranes is in essential agreement with the model.
Received: 6 January 1997/Revised: 6 June 1997 相似文献
17.
Calcium-pumping ATPases in vesicles from carrot cells : stimulation by calmodulin or phosphatidylserine, and formation of a 120 kilodalton phosphoenzyme 总被引:12,自引:10,他引:2
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Ca2+-ATPases keep cytoplasmic [Ca2+] low by pumping Ca2+ into intracellular compartments or out of the cell. The transport properties of Ca2+-pumping ATPases from carrot (Daucus carota cv Danvers) tissue culture cells were studied. ATP-dependent Ca2+ transport in vesicles that comigrated with an endoplasmic reticulum marker, was stimulated three- to fourfold by calmodulin. Cyclopiazonic acid (a specific inhibitor of the sarcoplasmic/endoplasmic reticulum Ca2+-ATPase) partially inhibited oxalate-stimulated Ca2+ transport activity; however, it had no effect on calmodulin-stimulated Ca2+ uptake driven by ATP or GTP. The results would suggest the presence of two types of Ca2+-ATPases, an endoplasmic reticulum- and a plasma membrane-type. Interestingly, incubation of membranes with [gamma32P]ATP resulted in the formation of a single acyl [32P]phosphoprotein of 120 kilodaltons. Formation of this phosphoprotein was dependent on Ca2+, but independent of Mg2+. Its enhancement by La3+ is characteristic of a phosphorylated enzyme intermediate of a plasma membrane-type Ca-ATPase. Calmodulin stimulated Ca2+ transport was decreased by W-7 (a calmodulin antagonist), ML-7 (myosin light chain kinase inhibitor) or thyroxine. Acidic phospholipids, like phosphatidylserine, stimulated Ca2+ transport, similar to their effect on the erythrocyte plasma membrane Ca2+-ATPase. These results would indicate that the calmodulin-stimulated Ca2+ transport originated in large part from a plasma membrane-type Ca2+ pump of 120 kilodaltons. The possibility of calmodulin-stimulated Ca2+-ATPases on endomembranes, such as the endoplasmic reticulum and secretory vesicles, as well as the plasma membrane is suggested. 相似文献
18.
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
19.
La3+ ions are known to antagonize Ca2+ and are used as a Ca2+ channel blocker but little is known on the direct effects of La3+. Micromolar La3+ concentrations promoted root growth while higher concentrations were inhibitory. The uptake of La3+ in maize root protoplasts revealed a membrane binding component (0.14 and 0.44 pmol min–1 protoplast–1 for 100 and 1,000 M La3+) followed by a slower concentration and time-dependent uptake. Uptake was reduced by Ca2+, but had no substantial effect on other ions. La3+ shifted microtubule organization from random to parallel but caused aggregation of microfilaments. Our data suggest that La3+ is taken up into plant cells and affects growth via stabilization of the cytoskeleton. 相似文献
20.
Membrane potential-dependent calcium transport in right-side-out plasma membrane vesicles from Zea mays L. roots 总被引:7,自引:1,他引:6
Jacqueline Marshall Alfonso Corzo Roger A. Leigh Dale Sanders 《The Plant journal : for cell and molecular biology》1994,5(5):683-694
Right-side-out plasma membrane vesicles isolated from Zea mays roots were used to study membrane potential (ΔΨ)-dependent Ca2+ transport. Membrane potentials were imposed on the vesicles using either K+ concentration gradients and valinomycin or SCN concentration gradients, and the size of the imposed ΔΨ was measured with [14C]tetraphenylphosphonium. Uptake of 45Ca2+ into the vesicles was stimulated by inside-negative ΔΨ. The rate of transport increased to a maximum at a ΔΨ of about -80 mV and then declined at more negative ΔΨ. When extravesicular Ca2+ concentration was varied, uptake was maximal in the range 100–200 μM Ca2+. Neither dihydropyridine nor phenylalkylamine Ca2+ channel blockers had any effect on Ca2+ uptake but 30 μM ruthenium red was completely inhibitory with half maximal inhibition at 10–15 μM ruthenium red. Calcium transport was also inhibited by inorganic cations. Zn2+, Gd3+ and Mg2+ inhibited by a maximum of 30% while La3+, Nd3+ and Mn2+ inhibited by 70%. The inhibitory effects of La3+ and Gd3+ were additive. Lanthanum-insensitive Ca2+ five Ca2+ transport was totally inhibited by 80 μM Gd3+ and showed maximum activity at a ΔΨ of -60 mV, with less uptake at both higher and lower ΔΨ. Lanthanum and Gd3+ also inhibited Ca2+ uptake into protoplasts isolated from Zea roots and their individual and combined effects were similar in extent to those observed with plasma membrane vesicles. It is concluded that maize root plasma membrane contains two Ca2+-permeable channels that can be distinguished by their susceptibility to inhibition by La3+ and Gd3+. Both are inhibited by ruthenium red but not by other organic Ca2+ channel blockers. 相似文献