共查询到20条相似文献,搜索用时 15 毫秒
1.
The interaction of pore-forming agents, such as Sendai virus, influenza virus (at pH 5 3), activated complement,Staphylococcus aureus α-toxin, melittin and polylysine, with the surface membrane of cells has been studied. In each case the following changes are
initiated: collapse of membrane potential, leakage of ions, and leakage of phosphorylated metabolites. The changes can be
inihibited by extracellular Ca2+ at physiological concentration; Mg2+ is less effective, and Zn2+ is more effective, than Ca2+ Ca2+ appears to act at a stage subsequent to the binding of pore-forming agent to cells. It is concluded that divalent cations
are able to protect cells against the damaging effects of certain viruses, toxins or the components of activated complement
in a manner that is worthy of further investigation. 相似文献
2.
Haemolysis by Sendal virus, -toxin, and activated complement is inhibited by high concentrations of divalent cations. In Daudi cells, sublytic amounts of these agents induce the following changes: collapse of surface membrane potential, uptake of Na+ and loss of K+ from cells, and leakage of phosphorylated metabo-tites from cells. The changes induced by Sendal virus and complement are sensitive to physiological concentrations of extracellular Ca2+. It is concluded that fluctuations in plasma Ca2+ concentration may affect the damaging action of certain pore-forming agents on susceptible cells. 相似文献
3.
Karl E. O. Åkerman 《Journal of bioenergetics and biomembranes》1977,9(1):65-72
Plots relating the initial rate of mitochondrial Ca2+ transport to the Ca2+ concentration (kinetic plots) have a hyperbolic shape in a Ca2+ concentration range of 2.5–100 µM as measured in sucrose or KCl media. In the presence of Mg2+ or a polyamine spermine, which both are competitive inhibitors of Ca2+ binding to low affinity sites at the membrane surface, the shape of the plots becomes sigmoidal. At higher concentrations of these agents linear kinetic plots are obtained as measured in a sucrose medium. In a KCl medium the sigmoidality of the kinetic plots is enhanced by an increase in the Mg2+ or spermine concentration. It is suggested that Mg2+ and spermine affect the kinetics of Ca2+ transport by interfering with Ca2+ binding to low affinity sites of the membrane surface and that the binding of Ca2+ to these sites is the first step of the mitochondrial Ca2+ transport. 相似文献
4.
C. A. Pasternak 《Bioscience reports》1987,7(2):81-91
This review focusses on two questions: (1) How can the intracellular toxicity of ions such as Ca2+ or Zn2+ be reconciled with their extracellular benefit? (2) Why is the dietary requirement for Zn2+ so high when its documented biological role is that of a tightly-bound prosthetic group of certain enzymes? An answer to both questions is provided by the observation that extracellular cations such as Ca2+ and Zn2+ protect the plasma membrane of cells against non-specific leakage, including an influx of Ca2+ or Zn2+. It is suggested that such protection, against leakage induced by microbial and other toxins, may contribute to the high dietary requirement for zinc. These arguments lead to the proposal that a previously unrecognized form of host defence is one of protection of the cell plasma membrane by divalent cations against damage induced by cytotoxic agents of environmental origin. 相似文献
5.
Effect of Ca2+ on the detoxification of Cd2+ byScenedesmus obliquus cells at low or high temperature
Scenedesmus obliquus was incubated with Cd2+ in the presence or absence of calcium at low (10°C) or high (40°C) temperature. The Cd2+ uptake was affected not only by Ca2+ but also by temperature. Growth rate was inhibited by Cd2+ especially at low temperature. In all Ca2+-containing cultures,S. obliquus exhibited higher rates of growth, dry matter and pigment fractions than in those containing Cd2+ alone. Proteins exhibited a similar response. Ca2+ in the presence of Cd2+ was most efficient where protein contents were mostly doubled. On the other hand Ca2+ reduced the solute leakage by the test alga at 10 and 40°C. 相似文献
6.
《生物化学与生物物理学报:生物膜》1987,905(1):9-16
The results shown in this paper indicate that the permeability properties of egg yolk phosphatidylcholine sonicated vesicles as detected by the leakage of carboxy fluorescein changes according to the Ca2+ content. Vesicles containing Ca2+ show a higher rate of leakage than those containing Na+ solutions in response to the increase of Ca2+ concentration in the outer solution. The results are interpreted in terms of the rigidity promoted by Ca2+ and are compared to those obtained with long and short chain alcohols. 相似文献
7.
Curtis W. Hoganson Demetrios F. Ghanotakis Gerald T. Babcock Charles F. Yocum 《Photosynthesis research》1989,22(3):285-293
Manganese in the oxygen-evolving complex is a physiological electron donor to Photosystem II. PS II depleted of manganese may oxidize exogenous reductants including benzidine and Mn2+. Using flash photolysis with electron spin resonance detection, we examined the room-temperature reaction kinetics of these reductants with Yz
+, the tyrosine radical formed in PS II membranes under illumination. Kinetics were measured with membranes that did or did not contain the 33 kDa extrinsic polypeptide of PS II, whose presence had no effect on the reaction kinetics with either reductant. The rate of Yz
+ reduction by benzidine was a linear function of benzidine concentration. The rate of Yz
+ reduction by Mn2+ at pH 6 increased linearly at low Mn2+ concentrations and reached a maximum at the Mn2+ concentrations equal to several times the reaction center concentration. The rate was inhibited by K+, Ca2+ and Mg2+. These data are described by a model in which negative charge on the membrane causes a local increase in the cation concentration. The rate of Yz
+ reduction at pH 7.5 was biphasic with a fast 400 s phase that suggests binding of Mn2+ near Yz
+ at a site that may be one of the native manganese binding sites.Abbreviations PS II
Photosystem II
- YD
tyrosine residue in Photosystem II that gives rise to the stable Signal II EPR spectrum
- Yz
tyrosine residue in Photosystem II that mediates electron transfer between the reaction center chlorophyll and the site of water oxidation
- ESR
electron spin resonance
- DPC
diphenylcarbazide
- DCIP
dichlorophenolindophenol 相似文献
8.
Vincenzo Panagia Vijayan Elimban Pallab K. Ganguly Naranjan S. Dhalla 《Molecular and cellular biochemistry》1987,78(1):65-71
Heart sarcolemma has been shown to possess three catalytic sites (I, II and III) for methyl transferase activity (Panagia V, Ganguly PK and Dhalla NS. Biochim Biophys Acta 792: 245–253, 1984). In this study we examined the effect of phosphatidylethanolamine N-methylation on ATP-independent Ca2+ binding and ATPase activities in isolated rat heart sarcolemma. Both low affinity (1.25 mM Ca2+) and high affinity (50 µM Ca2+) Ca2+ binding activities were decreased following incubation of sarcolemmal membranes with AdoMet under optimal conditions for site II and III. Similarly, Ca2+ ATPase activities measured at 1.25 mM and 4 mM Ca2+ were depressed by phospholipid N-methylation. S-adenosyl homocysteine, a specific inhibitor of phospholipid N-methylation, prevented the depression of low affinity Ca2+ binding and Ca2+ ATPase activities, whereas the methylation-induced effect on the high affinity Ca2+ binding was not influenced by this agent. Pretreatment of sarcolemma with methyl acetimidate hydrochloride, an amino group blocking agent, also prevented the methylation-induced inhibition of both Ca2+ binding and Ca2+ ATPase. A further decrease in Ca2+ binding and Ca2+ ATPase activities together with a marked increase in the intramembranal level of PC was seen when membranes were methylated under the site III conditions in the presence of phosphatidyldimethylethanolamine as exogenous substrate. There was no effect of phospholipid methylation on sarcolemmal Na+-K+ ATPase and Mg2+ ATPase activities. These results indicate a role of phospholipid N-methylation in the regulation of sarcolemmal Ca2+ ATPase and low affinity ATP-independent Ca2+ binding. 相似文献
9.
《Biochimica et Biophysica Acta (BBA) - Protein Structure and Molecular Enzymology》1983,742(1):135-141
Muscle G-actin was polymerized by addition of 2 mM Mg2+ or 2 mM Ca2+. Subsequent addition of formamide reduced the specific viscosity of the polymer solution. However, kinetic analysis of this reduction in the presence or absence of 0.1 M KCl revealed differences between F-actin formed in the presence of Mg2+ and F-actin formed in the presence of Ca2+. In the presence of Mg2+ the viscosity dropped instantaneously, reaching within minutes a steady-state level that was constant for many hours. In contrast, in the presence of Ca2+ the high-shear viscosity continued to decrease slowly after an initial drop, and it could take hours until a quasi-equilibrium was obtained. The time was dependent on both formamide and protein concentration. Addition of formamide increased the critical actin concentration in the presence of Ca2+, but not in the presence of Mg2+. This is taken as evidence that in the presence of Ca2+, but not in the presence of Mg2+, formamide causes partial depolymerization of F-actin. 相似文献
10.
《生物化学与生物物理学报:生物膜》2023,1865(6):184161
Human islet amyloid polypeptide (hIAPP, also known as amylin) is a 37 amino acid pancreatic polypeptide hormone that plays a role in regulating glucose levels, but forms pancreatic amyloid in type-2 diabetes. The process of amyloid formation by hIAPP contributes to β-cell death in the disease. Multiple mechanisms of hIAPP induced toxicity of β-cells have been proposed including disruption of cellular membranes. However, the nature of hIAPP membrane interactions and the effect of ions and other molecules on hIAPP membrane interactions are not fully understood. Many studies have used model membranes with a high content of anionic lipids, often POPS, however the concentration of anionic lipids in the β-cell plasma membrane is low. Here we study the concentration dependent effect of Ca2+ (0 to 50 mM) on hIAPP membrane interactions using large unilamellar vesicles (LUVs) with anionic lipid content ranging from 0 to 50 mol%. We find that Ca2+ does not effectively inhibit hIAPP amyloid formation and hIAPP induced membrane leakage from binary LUVs with a low percentage of POPS, but has a greater effect on LUVs with a high percentage of POPS. Mg2+ had very similar effects, and the effects of Ca2+ and Mg2+ can be largely rationalized by the neutralization of POPS charge. The implications for hIAPP-membrane interactions are discussed. 相似文献
11.
We investigated the cytosolic free calcium concentration ([Ca2+]i) of leech Retzius neurons in situ while varying the extracellular Ca2+ concentration via the bathing solution ([Ca2+]B). Changing [Ca2+]B had only an effect on [Ca2+]i if the cells were depolarized by raising the extracellular K+ concentration. Surprisingly, raising [Ca2+]B from 2 to 10 mm caused a decrease in [Ca2+]i, and an increase was evoked by reducing [Ca2+]B to 0.1 mm. These changes were not due to shifts in membrane potential. At low [Ca2+]B moderate membrane depolarizations were sufficient to evoke a [Ca2+]i increase, while progressively larger depolarizations were necessary at higher [Ca2+]B. The changes in the relationship between [Ca2+]i and membrane potential upon varying [Ca2+]B could be reversed by changing extracellular pH. We conclude that [Ca2+]B affects [Ca2+]i by modulating Ca2+ influx through voltage-dependent Ca2+ channels via the electrochemical Ca2+ gradient and the surface potential at the extracellular side of the plasma membrane. These two parameters are affected in
a counteracting way: Raising the extracellular Ca2+ concentration enhances the electrochemical Ca2+ gradient and hence Ca2+ influx, but it attenuates Ca2+ channel activity by shifting the extracellular surface potential to the positive direction, and vice versa.
Received: 23 January 2001/Revised: 23 June 2001 相似文献
12.
Sidney Katz Basil D. Roufogalis Amiram D. Landman Larry Ho 《Journal of cellular biochemistry》1979,10(2):215-225
Erythrocyte membranes prepared by three different procedures showed (Mg2+ + Ca2+)-ATPase activities differing in specific activity and in affinity for Ca2+. The (Mg2+ + Ca2+)-ATPase activity of the three preparations was stimulated to different extents by a Ca2+-dependent protein activator isolated from hemolystes. The Ca2+ affinity of the two most active preparations was decreased as the ATP concentration in the assay medium was increased. Lowering the ATP concentration from 2 mM to 2–200 μM or lowering the Mg:ATP ratio to less than one shifted the (Mg2+ + Ca2+)-ATPase activity in stepwise hemolysis membranes from mixed “high” and “low” affinity to a single high Ca2+ affinity. Membranes from which soluble proteins were extracted by EDTA (0.1 mM) in low ionic strengh, or membranes prepared by the EDTA (1–10 mM) procedure, did not undergo the shift in the Ca2+ affinity with changes in ATP and MgCl2 concentrations. The EDTA-wash membranes were only weakly activated by the protein activator. It is suggested that the differences in properties of the (Mg2+ + Ca2+)-ATPase prepared by these three procedures reflect differences determined in part by the degree of association of the membrane with a soluble protein activator and changes in the state of the enzyme to a less activatable form. 相似文献
13.
G.M. Roomans A.P.R. Theuvenet Th.P.R. Van Den Berg G.W.F.H. Borst-Pauwels 《生物化学与生物物理学报:生物膜》1979,551(1):187-196
The uptake of Ca2+ and Sr2+ by the yeast Saccharomyces cerevisiae is energy dependent, and shows a deviation from simple Michaelis-Menten kinetics. A model is discussed that takes into account the effect of the surface potential and the membrane potential on uptake kinetics.The rate of Ca2+ and Sr2+ uptake is influenced by the cell pH and by the medium pH. The inhibition of uptake at low concentrations of Ca2+ and Sr2+ at low pH may be explained by a decrease of the surface potential.The inhibition of Ca2+ and Sr2+ uptake by monovalent cations is independent of the divalent cation concentration. The inhibition shows saturation kinetics, and the concentration of monovalent cation at which half-maximal inhibition is observed, is equal to the affinity constant of this ion for the monovalent cation transport system. The inhibition of divalent cation uptake by monovalent cations appears to be related to depolarization of the cell membrane.Phosphate exerts a dual effect on uptake of divalent cations: and initial inhibition and a secondary stimulation. The inhibition shows saturation kinetics, and the inhibition constant is equal to the affinity constant of phosphate for its transport mechanism. The secondary stimulation can only partly be explained by a decrease of the cell pH, suggesting interaction of intracellular phosphate, or a phosphorylated compound, with the translocation mechanism. 相似文献
14.
Summary The preincubation of the rat red blood cell membranes in the presence of low Ca2+ levels causes an irreversible inhibition of the Ca2+-stimulated ATPase activity. The inactivation is dependent on the Ca2+ concentration and the apparent Ki is identical to the Ca2+ concentration needed to reach the half-maximal activity of the enzyme. This fact and the energy of activation (Ea = 13.8 Kcal/mol) for the inhibition suggest that Ca2+ inactivates the Ca2+-stimulated ATPase by binding to the same site which it normally occupies to activate the enzyme. It is concluded that the Ca2+-stimulated ATPase is in a dynamic equilibrium between two states: a stable ATP-bound state and an unstable ATP-free state. 相似文献
15.
Summary Rhabdomeral microvilli of photoreceptors of the blowfly Lucilia are shown to contain a cytoskeleton. An axial filament ( 6–11 nm) in each microvillus is inserted into a terminal cap distally, and into a plug filling the narrow neck of the microvillus proximally. In some states, the axial filament projects beyond the neck; within the microvillus it is surrounded by amorphous material. Together, they form an axial complex, which supports side-arms linking it to the plasma membrane. Conventional fixation for examination with the electron microscope destroys the cytoskeleton. To preserve it, retinae are pre-treated with a Ringer's solution buffered with 20 mM imidazole and containing, minimally, the following components: (i) a protease inhibitor, usually phenylmethylsulphonyl-fluoride (PMSF); (ii) either the Ca2+-chelator EGTA, or the calmodulin-blocking agent trifluoperazine (TFP); and (iii) a source of divalent cations to preserve the side-arms. When EGTA is used, Mg2+, Sr2+, Ba2+, Mn2+ and Co2+ are effective, Ba2+ giving the most satisfactory contrast, and Mg2+ and Co2+ the best preservation. It is inferred that the cytoskeletal complex includes at least one Ca2+-activated protease, and possibly calmodulin. Microvilli are bonded together by intermicrovillar bridges with a periodicity of 11–17nm. The cytoskeleton is destroyed by pretreatment with 1 mM dithiothreitol (DTT), possibly by the activation of a thiol protease. It does not survive osmication unless treated with low molecular weight tannic acid (LMWT). The evidence does not discriminate between actin and intermediate filaments as the basis of the cytoskeleton. Attention is drawn to similarities and differences between the rhabdomeral cytoskeleton and that of vertebrate intestinal brush-borders. The extreme lability of the rhabdomeral cytoskeleton to conventional methods of fixation is attributed in part to the Ca2+ fluxes experienced by invertebrate photoreceptors, and in part to the effects of osmication.The authors thank Dr. Lindsay Barton-Brown and Tom Van Gerwen for supplying flies from CSIRO cultures: Smith Kline and French Laboratories Ltd., French's Forest, N.S.W. for a generous gift of trifluoperazine, and Mallinckrodt, Inc., St. Louis, Missouri, USA, for a gift of low molecular weight tannic acid. Many colleagues, especially Richard Payne, Steve Shaw and Gert De Couet helped by discussing the results. George Weston and the staff of the Electron Microscope Unit provided support and advice. Sandy Smith prepared Table 1 相似文献
16.
Giuseppe Inesi Francesco Tadini-Buoninsegni 《Journal of cell communication and signaling》2014,8(1):5-11
The Ca2+ transport ATPase (SERCA) of sarcoplasmic reticulum (SR) plays an important role in muscle cytosolic signaling, as it stores Ca2+ in intracellular membrane bound compartments, thereby lowering cytosolic Ca2+ to induce relaxation. The stored Ca2+ is in turn released upon membrane excitation to trigger muscle contraction. SERCA is activated by high affinity binding of cytosolic Ca2+, whereupon ATP is utilized by formation of a phosphoenzyme intermediate, which undergoes protein conformational transitions yielding reduced affinity and vectorial translocation of bound Ca2+. We review here biochemical and biophysical evidence demonstrating that release of bound Ca2+ into the lumen of SR requires Ca2+/H+ exchange at the low affinity Ca2+ sites. Rise of lumenal Ca2+ above its dissociation constant from low affinity sites, or reduction of the H+ concentration by high pH, prevent Ca2+/H+ exchange. Under these conditions Ca2+ release into the lumen of SR is bypassed, and hydrolytic cleavage of phosphoenzyme may yield uncoupled ATPase cycles. We clarify how such Ca2+pump slippage does not occur within the time length of muscle twitches, but under special conditions and in special cells may contribute to thermogenesis. 相似文献
17.
We reported previously that a Ca2+-ATPase in rat testes and goat spermatozoa could be activated by Ca2+ alone without Mg2+, though it has a lot of similarities with the well known Ca2+, Mg2+-ATPase. Recently, we were successful in isolating the phosphorylated intermediate of the former enzyme under control conditions
i.e., in the presence of low concentration of Ca2+ and at low temperature. Increase of the concentration of Ca2+ and/or temperature lead to dephosphorylation. Based on our observations, we proposed a reaction scheme comparable to that
of Ca2+, Mg2+-ATPase. The findings strengthened our previous report that Mg2+-independent Ca2+-ATPase is involved in Ca2+ transport and Ca2+ uptake like Ca2+, Mg2+-ATPase. 相似文献
18.
The effect of calcium and a soluble cytoplasmic activator on (Ca2+ + Mg2+)-ATPase of density-separated human red cells was investigated. At all calcium concentrations tested, dense (old) lysed cells and their isolated membranes displayed lower activities as compared to the light (young) cells and their membranes. Isolated membranes from all density red cell fractions showed two distinct (Ca2+ + Mg2+)-ATPase activities; one at low calcium and another at moderate calcium concentrations. At high calcium concentration, (Ca2+ + Mg2+)-ATPase activity of isolated membranes was low in all cell fractions. In contrast to the isolated membranes, lysed cells from all density fractions had a maximum (Ca2+ + Mg2+)-ATPase activity only at a low concentration of calcium, while moderate and high calcium concentrations produced low activity. Upon isolation of membranes, a substantial loss of (Ca2+ + Mg2+)-ATPase activity took place from all density cell fractions. Upon membrane isolation, the relative loss of (Ca2+ + Mg2+)-ATPase activity at low Ca2+ concentration was greater in older cells. The extent of stimulation of (Ca2+ + Mg2+)-ATPase by the activator at low calcium concentration was 3–4-fold greater in older cell membranes than in the young ones.These data suggest that the lower (Ca2+ + Mg2+)-ATPase activity in old cells could be accounted for by a selective loss of (Ca2+ + Mg2+)-ATPase activity at low Ca2+ concentration presumably due to reduced affinity of old cell membranes to activator protein. 相似文献
19.
The concentration of intracellular calcium, [Ca2+]
i
, in Paramecium was imaged during cold-sensitive response by monitoring fluorescence of two calcium-sensitive dyes, Fluo-3 and Fura-Red.
Cooling of a deciliated Paramecium caused a transient increase in [Ca2+]
i
at the anterior region of the cell. Increase in [Ca2+]
i
was not observed at any region in Ca2+-free solution. Under the electrophysiological recording, a transient depolarization of the cell was observed in response
to cooling. On the voltage-clamped cell, cooling induced a transient inward current under conditions where K+ currents were suppressed. These membrane depolarizations and inward currents in response to cooling were lost upon removing
extracellular Ca2+. The cold-induced inward current was lost upon replacing extracellular Ca2+ with equimolar concentration of Co2+, Mg2+ or Mn2+, but it was not affected significantly by replacing with equimolar concentration of Ba2+ or Sr2+. These results indicate that Paramecium cells have Ca2+ channels that are permeable to Ca2+, Ba2+ and Sr2+ in the anterior soma membrane and the channels are opened by cooling.
Received: 1 April 1996/Revised: 23 July 1996 相似文献
20.
Excess Mn2+ in humans causes a neurological disorder known as manganism, which shares symptoms with Parkinson's disease. However, the cellular mechanisms underlying Mn2+‐neurotoxicity and the involvement of Mn2+‐transporters in cellular homeostasis and repair are poorly understood and require further investigation. In this work, we have analyzed the effect of Mn2+ on neurons and glia from mice in primary cultures. Mn2+ overload compromised survival of both cell types, specifically affecting cellular integrity and Golgi organization, where the secretory pathway Ca2+/Mn2+‐ATPase is localized. This ATP‐driven Mn2+ transporter might take part in Mn2+ accumulation/detoxification at low loads of Mn2+, but its ATPase activity is inhibited at high concentration of Mn2+. Glial cells appear to be significantly more resistant to this toxicity than neurons and their presence in cocultures provided some protection to neurons against degeneration induced by Mn2+. Interestingly, the Mn2+ toxicity was partially reversed upon Mn2+ removal by wash out or by the addition of EDTA as a chelating agent, in particular in glial cells. These studies provide data on Mn2+ neurotoxicity and may contribute to explore new therapeutic approaches for reducing Mn2+ poisoning. 相似文献