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1.
Stimulation of hamster lymph node cells, splenocytes and thymocytes by the mitogen phytohemagglutinin-P (PHA) was found to be greatly enhanced by addition of 1–10 mM LiCl to the cultures. Lithium enhanced stimulation, as determined by [3H]TdR incorporation, only if added within the first 24 h of culture. The enhancing effect of lithium was specific for this monovalent cation since equivalent concentrations of KCl or NaCl did not induce a similar effect on [3H]TdR incorporation. The divalent cations Mg2+ (1–10 mM) and Ca2+ (1-1.6 mM), also had an enhancing effect on PHA stimulation. However, addition of Li+ to cultures enhanced with Mg2+ and/or Ca2+ led to an additional potentiation of the response to PHA. These results suggest that Li+ modifies a unique early event during stimulation of lymphoid cells by this mitogen.  相似文献   

2.
Addition of LiCl (1–25 mM) to serum-free cultures of MHA hamster thymocytes, lymph node cells, or splenocytes stimulated with concanavalin A had a biphasic effect on [3H]thymidine incorporation. These concentrations of LiCl enhanced stimulation of [3H]thymidine incorporation by suboptimal levels of concanavalin A but inhibited stimulation of optimal and supraoptimal concentrations of concanavalin A. This effect was specific for Li+ since it was not observed when similar concentrations of Na+, K+, or Mg2+ were added to cultures stimulated by concanavalin A. The inhibitory effect of LiCl on concanavalin A stimulation was not reversed by addition of Na+, Ca2+, Mg2+, or Ca2+ + Mg2+ to the cultures. Significant reversal of LiCl inhibition of stimulation was observed when KCl was added to the cultures. However none of the ions tested blocked the Li-induced enhancement of [3H]thymidine incorporation in the presence of suboptimal concentrations of concanavalin A.  相似文献   

3.
The P2U purinergic agonist ATP (0.3 mM) elicited an increase in [Ca2+]i due to Ca2+ release from intracellular stores in transfected Chinese hamster ovary cells that express the bovine cardiac Na+/Ca2+ exchanger (CK1.4 cells). The following observations indicate that ATP-evoked Ca2+ release was accompanied by a Ca2+- dependent regulatory activation of Na+/Ca2+ exchange activity: Addition of extracellular Ca2+ (0.7 mM) 0–1 min after ATP evoked a dramatic rise in [Ca2+]i in Na+-free media (Li+ substitution) compared to Na+-containing media; no differences between Na+- and Li+-based media were observed with vector-transfected cells. In the presence of physiological concentrations of extracellular Na+ and Ca2+, the ATP-evoked rise in [Ca2+]i declined more rapidly in CK1.4 cells compared to control cells, but then attained a long-lived plateau of elevated [Ca2+]i which eventually came to exceed the declining [Ca2+]i values in control cells. ATP elicited a transient acceleration of exchange-mediated Ba2+ influx, consistent with regulatory activation of the Na+/Ca2+ exchanger. The acceleration of Ba2+ influx was not observed in vector-transfected control cells, or in CK1.4 cells in the absence of intracellular Na+ or when the Ca2+ content of the intracellular stores had been reduced by prior treatment with ionomycin. The protein kinase C activator phorbol 12-myristate 13-acetate attenuated the exchange-mediated rise in [Ca2+]i under Na+-free conditions, but did not inhibit the ATP-evoked stimulation of Ba2+ influx. The effects of PMA are therefore not due to inhibition of exchange activity, but probably reflect the influence of protein kinase C on other Ca2+ homeostatic mechanisms. We conclude that exchange activity is accelerated during ATP-evoked Ca2+ release from intracellular stores through regulatory activation by increased [Ca2+]i. In the absence of extracellular Ca2+, the stimulation of exchange activity is short-lived and follows the time course of the [Ca2+]i transient; in the presence of extracellular Ca2+, we suggest that the exchanger remains activated for a longer period of time, thereby stabilizing and prolonging the plateau phase of store-dependent Ca2+ entry.  相似文献   

4.
Glutathione reductase (GR; E.C. 1.6.4.2) is a flavoprotein that catalyzes the NADPH-dependent reduction of oxidized glutathione (GSSG). In this study we tested the effects of Al3+, Ba2+, Ca2+, Li+, Mn2+, Mo6+, Cd2+, Ni2+, and Zn2+ on purified bovine liver GR. In a range of 10?μM–10?mM concentrations, Al3+, Ba2+, Li+, Mn2+, and Mo6+, and Ca2+ at 5?μM–1.25?mM, had no effect on bovine liver GR. Cadmium (Cd2+), nickel (Ni2+), and zinc (Zn2+) showed inhibitory effects on this enzyme. The obtained IC50 values of Cd2+, Ni2+, and Zn2+ were 0.08, 0.8, and 1?mM, respectively. Cd2+ inhibition was non-competitive with respect to both GSSG (KiGSSG 0.221?±?0.02?mM) and NADPH (KiNADPH 0.113?±?0.008?mM). Ni2+ inhibition was non-competitive with respect to GSSG (KiGSSG 0.313?±?0.01?mM) and uncompetitive with respect to NADPH (KiNADPH 0.932?±?0.03?mM). The effect of Zn2+ on GR activity was consistent with a non-competitive inhibition pattern when the varied substrates were GSSG (KiGSSG 0.320?±?0.018?mM) and NADPH (KiNADPH 0.761?±?0.04?mM), respectively.  相似文献   

5.
Stimulation of hamster thymocytes, splenocytes, or lymph node cells occurred to a minimal extent in the absence of K+. This observation was found for stimulation by T-cell mitogens (phytohemagglutinin and concanavalin A), A B-cell mitogen (lipopolysaccharide), or antigen (KLH). Marginal restoration of the responses to these stimulants occurred in the presence of 0.1 mM K+ and responsiveness returned to near maximal levels on addition of 1 mM K+ to the cultures. Attempts to restore the responsiveness with other monovalent cations revealed an order of effectiveness of K+ ≥ Rb+ ? NH4+ ≥ Li+. At the 1 mM level K+ and Rb+ were equally effective in supporting stimulation by phytohemagglutinin while all concentrations of Li+ tested (0.1–10 mM) would not support stimulation. However, addition of Li+ to cultures reconstituted with 1 mM K+ or Rb+ revealed that this ion could enhance the phytohemagglutinin response by approximately 100% in the presence of K+ and only 30% in the presence of Rb+. These data support the hypotheses that the Na,K ATPase must be active for lymphocyte stimulation to occur and that some of the biological effects of Li+ on lymphocyte stimulation are mediated at the level of the Na,K ATPase.  相似文献   

6.
Two extracellular peroxidases from Phanerochaete chrysosporium, namely a lignin peroxidase (LiP) and manganese peroxidase (MnP), were purified simultaneously by applying successively, ultrafiltration, ion-exchange and gel filtration chromatography. LiP and MnP have a molecular mass of 36 and 45 kDa, respectively. The optimal pHs for LiP and MnP activities were 3.0 and 4.5, respectively. Both peroxidases showed maximal activity at 30 °C and moderate thermostability. MnP activity was strongly inhibited by Fe2+, Zn2+, Mg2+ and Hg2+, and enhanced by Mn2+, Ca2+ and Cu2+. LiP activity was enhanced by Ca2+, Na+ and Co2+ and it was inhibited in the presence of K+, Hg+, Fe2+, Mg2+ and high concentrations of Cu2+ and Zn2+. The Km and Vmax for LiP toward veratryl alcohol as a substrate were 0.10 mM and 15.2 U mg−1, respectively and for MnP toward Mn2+, they were respectively 0.03 mM and 25.5 U mg−1. The two peroxidases were also able to break down rice lignin in a small-scale solid state treatment system. Data suggest these two peroxidases may be considered as potential candidates for the development of enzyme-based technologies for lignin degradation.  相似文献   

7.
The extracellular phytase in the supernatant of cell culture of the marine yeast Kodamaea ohmeri BG3 was purified to homogeneity with a 7.2-fold increase in specific phytase activity as compared to that in the supernatant by ammonium sulfate fractionation, gel filtration chromatography (Sephadex™ G-75), and anion-exchange chromatography (DEAE Sepharose Fast Flow Anion-Exchange). According to the data from sodium dodecyl sulfate-polyacrylamide gel electrophoresis, the molecular mass of the purified enzyme was estimated to be 98.2 kDa while the molecular mass of the purified enzyme was estimated to be 92.9 kDa and the enzyme was shown to be a monomer according to the results of gel filtration chromatography. The optimal pH and temperature of the purified enzyme were 5.0 and 65°C, respectively. The enzyme was stimulated by Mn2+, Ca2+, K+, Li+, Na+, Ba2+, Mg2+ and Co2+ (at a concentrations of 5.0 mM), but it was inhibited by Cu2+, Hg2+, Fe2+, Fe3+, Ag+, and Zn2+ (at a concentration of 5.0 mM). The enzyme was also inhibited by phenylmethylsulfonyl fluoride (PMSF), iodoacetic acid (at a concentration of 1.0 mM), and phenylgloxal hydrate (at a concentration of 5.0 mM), and not inhibited by EDTA and 1,10-phenanthroline (at concentrations of 1.0 mM and 5.0 mM). The K m, V max, and K cat values of the purified enzyme for phytate were 1.45 mM, 0.083 μmol/ml · min, and 0.93 s-1, respectively.  相似文献   

8.
How do heavy metals affect stomatal movements and whether water channels are involved in stomatal movements was investigated in broad bean (Vicia faba L.) leaves. Three-week old fully expanded leaves were harvested. Leaf epidermis was peeled off and soaked in the Mes–KOH buffer containing the salts of heavy metals. Stomatal aperture was measured under the microscope. The tested heavy metal ions, such as Hg2+, Pb2+, Zn2+, and La3+, partly inhibited stomatal opening in light or closing in darkness at submillimolar concentrations, while K+, Na+ and Mg2+ had no visible effects on stomatal movements. As compared to La3+, Hg2+ affected stomatal movements more significantly. Stomatal movements were almost completely inhibited under a combined Hg2+ and La3+ treatment. Apparently, La3+, a Ca2+ channel blocker, inhibits the changes in the cytosolic Ca2+ concentration in guard cells, thus affecting stomatal movements. The inhibitory effect of Hg2+ on stomatal movements may be explained by the inhibition of water channels. Like Hg2+, Zn2+ and Pb2+ interfered with stomatal movements. It is concluded that heavy metals at submillimolar concentrations inhibit stomatal movements. They may affect water fluxes through guard cell membranes in different ways, i.e., Hg2+, Pb2+, and Zn2+ inhibit water channels, whereas La3+ block ion channels. Water channels may be involved in stomatal movements by regulating water fluxes and play a dominant and primary role in stomatal movements.  相似文献   

9.
Novel phenanthroline Schiff base fluorescent sensors L1 , L2 , and D1 were designed and synthesized. The sensing abilities of the compounds in the presence of metal cations (Li+, Na+, K+, Ag+, Mg2+, Ba2+, Ca2+, Mn2+, Pb2+, Hg2+, Ni2+, Zn2+, Cd2+, Co2+, Cu2+, Cr3+, Fe3+, Fe2+, Al3+, and Eu3+) were studied by UV‐vis and fluorescent spectroscopy. The compounds L1 , L2 , and D1 could act as Eu3+ ion turn‐off fluorescent sensors based on ligand‐to‐metal binding mechanism in DMSO‐H2O solution (v/v = 1:1, 10 mM Tris, pH = 7.4). Additionally, the L1 –Eu3+ and D1 –Eu3+ complexes could be applied as turn‐on enantioselective sensors sensing of malate anion isomers with color changes. Furthermore, biological experiments using living PC‐12 cells demonstrated that L1 and D1 had excellent membrane permeability and could be used as effective fluorescent sensors for detecting Eu3+ and malate anion in living cells.  相似文献   

10.
The ability of trout to metabolize aniline in vitro in the presence of some divalent metal ions was investigated in the liver microsomes of rainbow trout, Salmo gairdneri. Trout liver microsomes were highly capable of catalyzing aniline hydroxylation to p-aminophenol with a specific activity of 0.068 nmoles/min per mg of microsomal protein in potassium phosphate buffer, pH 7.4 at 25°C. The activity of the aniline hydroxylase system was competitively inhibited by Hg+2, Ni+2, Cd+2, and Zn+2, while Cu+2 and Fe+3 seemed to inhibit the activity noncompetitively at 1 mM aniline concentrations. IC50 values at fixed aniline concentration were estimated to be 0.45 mM for Hg+2, Ni+2, and Cd+2, 1.8 mM for Zn+2 and Fe+3, and 1.3 mM for Cu+2. Eadie-Hofstee plots gave identical Vmax values of approximately 0.046 nmol/min per mg of protein while Km values were increased in the presence of Hg+2, Ni+2, CD+2, and Zn+2, indicating competitive inhibition. Both Km and Vmax values were affected by Fe+3 and Cu+2, suggesting noncompetitive inhibition. Ki values extracted from the Dixon plots were determined t be 0.23, 0.43, and 0.65 mM for Hg+2, Ni+2, and Cd+2, respectively, providing the most effective inhibition on the aniline hydroxylase system among studied metal ions. The Ki values were much higher in the presence of others. The results indicate a selective inhibition of the aniline hydroxylase system of trout liver microsomes by divalent metal ions. © 1997 John Wiley & Sons, Inc.  相似文献   

11.
Gow  I.F.  Flatman  P.W.  Ellis  D. 《Molecular and cellular biochemistry》1999,198(1-2):129-133
We have examined the effect of exposing isolated rat ventricular myocytes to lithium while measuring cytosolic free magnesium ([Mg2+]i) and calcium ([Ca2+]i) levels with the fluorescent, ion sensitive probes mag-fura-2 and fura-2. There was a significant rise in [Mg2+]i after a 5 min exposure to a solution in which 50% of the sodium had been replaced by Li+, but not when the sodium had been replaced by bis-dimethylammonium (BDA). However, there were significant increases in [Ca2+]i when either Na+ substitute was used. The possibility that Li+, which enters the cells, interferes with the signal from mag-fura-2 was eliminated as Li+ concentrations up to 10 mM had no effect on the dye's fluorescence signal. A possible explanation for these findings is that Li+ displaces Mg2+ from intracellular binding sites. Having considered the binding constants for Mg2+ and Li+ to ATP, we conclude that Li+ can displace Mg2+ from Mg-ATP, thus causing a rise in [Mg2+]i. This work has implications for other studies where Li+ is used as a Na+ substitute.  相似文献   

12.
Na+ (at a concentration of 10 mM) increased the uptake of succinate, glucose and l-valine by Micrococcus lysodeikucus cells considerably. The effect of Na+ could be duplicated by Li+ only, which, however, was less active. The other cations tested (K+, NH4+, Cs+, Mg2+, Ca2+ and Mn2+ were ineffective at concentrations up to 100 mM. Addition of Na+ increased the affinities of the uptake system for the substrate studied, while uptake capacity remained unaltered.  相似文献   

13.
In liver homogenate the biosynthesis ofN-acetylneuraminic acid usingN-acetylglucosamine as precursor can be followed stepwise by applying different chromatographic procedures. In this cell-free system 16 metal ions (Zn2+, Mn2+, La3+, Co2+, Cu2+, Hg2+, VO 3 , Pb2+, Ce3+, Cd2+, Fe2+, Fe3+, Al3+, Sn2+, Cs+ and Li+) and the selenium compounds, selenium(IV) oxide and sodium selenite, have been checked with respect to their ability to influence a single or possible several steps of the biosynthesis ofN-acetylneuraminic acid. It could be shown that the following enzymes are sensitive to these metal ions (usually applied at a concentration of 1 mmoll–1):N-acetylglucosamine kinase (inhibited by Zn2+ and vandate), UDP-N-acetylglucosamine-2-epimerase (inhibited by zn2+, Co2+, Cu2+, Hg2+, VO 3 , Pb2+, Cd2+, Fe3+, Cs+, Li+, selenium(IV) oxide and selenite), andN-acetylmannosamine kinase (inhibited by Zn2+, Cu2+, Cd2+, and Co2+). Dose dependent measurements have shown that Zn2+, Cu2+ and selenite are more efficient inhibitors of UDP-N-acetylglucosamine-2-epimerase than vanadate. As for theN-acetylmannosamine kinase inhibition, a decreasing inhibitory effect exists in the following order Zn2+, Cd2+, Co2+ and Cu2+. In contrast, La3+, Al3+ and Mn2+ (1 mmoll–1) did not interfere with the biosynthesis ofN-acetylneuraminic acid. Thus, the conclusion that the inhibitory effect of the metal ions investigated cannot be regarded as simply unspecific is justified.Dedicated to Professor Theodor Günther on the occasion of his 60th birthday  相似文献   

14.
Sodium concentrations as low as 2 mM exerted a significant protective effect on the high-pressure inactivation (160–210 MPa) of Rhodotorula rubra at pH 6.5, but not on two other yeasts tested (Shizosaccharomyces pombe and Saccharomyces cerevisiae). A piezoprotective effect of similar magnitude was observed with Li+ (2 and 10 mM), and at elevated pH (8.0–9.0), but no effect was seen with K+, Ca2+, Mg2+, Mn2+, or NH4 +. Intracellular Na+ levels in cells exposed to low concentrations of Na+ or to pH 8.0–9.0 provided evidence for the involvement of a plasma membrane Na+/H+ antiporter and a correlation between intracellular Na+ levels and pressure resistance. The results support the hypothesis that moderate high pressure causes indirect cell death in R. rubra by inducing cytosolic acidification.Communicated by K. Horikoshi  相似文献   

15.
Summary The cellular mechanisms by which nephrotoxic heavy metals injure the proximal tubule are incompletely defined. We used extracellular electrodes to measure the early effects of heavy metals and other sulfhydryl reagents on net K+ and Ca2+ transport and respiration (QO2) of proximal tubule suspensions. Hg2+, Cu2+, and Au3+ (10–4 m) each caused a rapid net K+ efflux and a delayed inhibition of QO2. The Hg2+-induced net K+ release represented passive K+ transport and was not inhibited by barium, tetraethylammonium, or furosemide. Both Hg2+ and Ag+ promoted a net Ca2+ uptake that was nearly coincident with the onset of the net K+ efflux. A delayed inhibition of ouabainsensitive QO2 and nystatin-stimulated QO2, indicative of Na+, K+-ATPase inhibition, was observed after 30 sec of exposure to Hg2+. More prolonged treatment (2 min) of the tubules with Hg2+ resulted in a 40% reduction in the CCCP-uncoupled QO2, indicating delayed injury to the mitochondria. The net K+ efflux was mimicked by the sulfhydryl reagents pCMBS and N-ethylmaleimide (10–4 m) and prevented by dithiothreitol (DTT) or reduced glutathione (GSH) (10–4 m). In addition, both DTT and GSH immediately reversed the Ag+-induced net Ca2+ uptake. Thus, sulfhydryl-reactive heavy metals cause rapid, dramatic changes in the membrane ionic permeability of the proximal tubule before disrupting Na+, K+-ATPase activity or mitochondrial function. These alterations appear to be the result of an interaction of the metal ions with sulfhydryl groups of cell membrane proteins responsible for the modulation of cation permeability.  相似文献   

16.
CHARACTERIZATION OF LYMPHOCYTE TRANSFORMATION INDUCED BY ZINC IONS   总被引:3,自引:0,他引:3       下载免费PDF全文
Lymphocyte cultures from all normal human adults are stimulated by zinc ions to increase DNA and RNA synthesis and undergo blast transformation. Optimal stimulation occurs at 0.1 mM Zn++. Examination of the effects of other divalent cations reveals that 0.01 mM Hg++ also stimulates lymphocyte DNA synthesis. Ca++ and Mg++ do not affect DNA synthesis in this culture system, while Mn++, Co++, Cd++, Cu++, and Ni++ at concentrations of 10-7–10-3 M are inhibitory. DNA and RNA synthesis and blast transformation begin to increase after cultures are incubated for 2–3 days with Zn++ and these processes reach a maximum rate after 6 days. The increase in Zn++-stimulated lymphocyte DNA synthesis is prevented by rendering cells incapable of DNA-dependent RNA synthesis with actinomycin D or by blocking protein synthesis with cycloheximide or puromycin. Zn++-stimulated DNA synthesis is also partially inhibited by 5'-AMP and chloramphenicol. Zn++ must be present for the entire 6-day culture period to produce maximum stimulation of DNA synthesis. In contrast to its ability to independently stimulate DNA synthesis, 0.1 mM Zn++ inhibits DNA synthesis in phytohemagglutinin-stimulated lymphocytes and L1210 lymphoblasts.  相似文献   

17.
Factor XIII catalyzes formation of γ-glutamyl-ε-lysyl crosslinks within fibrin clots. FXIII A2 can be activated proteolytically with thrombin and low mM Ca2+ or nonproteolytically with high monovalent/divalent cations along with low mM Ca2+. Physiologically, FXIII A2 is poised to respond to transient influxes of Ca2+ in a Na+ containing environment. A successful strategy to monitor FXIII conformational events is hydrogen–deuterium exchange (HDX) coupled with mass spectrometry. FXIII A2 was examined in the presence of different cations (Ca2+, Mg2+, Ba2+, Cu2+, Na+, TMAC+, and EDA2+) ranging from 1 to 2 mM, physiological Ca2+ concentration, to 50–500 mM for nonproteolytic activation. Increases in FXIII solvent exposure could already be observed at 1 mM Ca2+ for the dimer interface, the catalytic site, and glutamine substrate regions. By contrast, solvent protection was observed at the secondary cleavage site. These events occurred even though 1 mM Ca2+ is insufficient for FXIII activation. The metals 1 mM Mg2+, 1 mM Ba2+, and 1 mM Cu2+ each led to conformational changes, many in the same FXIII regions as Ca2+. FXIII could also be activated nonproteolytically with 500 mM tetramethylammonium chloride (TMAC+) and 500 mM ethylenediamine (EDA2+), both with 2 mM Ca2+. These different HDX studies help reveal the first FXIII segments that respond to physiological Ca2+ levels.  相似文献   

18.
1. Heavy metals (Hg2+, Cu2+, Cd2+, Zn2+, Pb2+) at micromolar concentrations strongly inhibit the Ca2+-ATPase activity present in the plasma-membrane obtained from the gill cells of Mytilus galloprovincialis Lam. Heavy metals act through inhibition of the formation of the phosphorylated intermediate.2. All the heavy metals tested inhibit the Ca2+-ATPase activity, the effect following the order: Hg2+ > Pb2+ > Cu2+ > Cd2+ > Zn2+; the simultaneous addition of different heavy metals causes a summatory inhibition of the enzyme activity; addition to the reaction mixture of GSH at a final concentration of 0.5 mM, reverses inhibitory effects of heavy metals.3. The inhibitory effects of Cu2+ on Ca2+-ATPase are highly enhanced by addition of ascorbate to the reaction mixture. In the presence of ascorbate (100 μM), copper strongly stimulates the lipid peroxidation damage of the gill plasma-membranes, a result that may explain the high copper cytotoxicity.  相似文献   

19.
Summary The effect of mercury (Hg2+) in the absence and presence of methylmercury (CH3Hg+), cadmium (Cd2+), copper (Cu2+), nickel (Ni2+) and calcium (Ca2+) on Nostoc calcicola Bréb. has been studied in terms of electrolyte leakage, NO3 uptake and in vivo nitrate reductase (NR) activity to discover any possible correlation among such parameters under Hg2+ stress. Leakage of electrolytes from Hg2+-treated cyanobacterial cells was directly proportional to Hg2+ concentrations and exposure time. In comparison to NO3 uptake, an about 60-fold slower rate of NR activity was observed in the untreated cultures, the former being five times more Hg2+-sensitive. A non-competitive synergistic interaction of Hg2+ with CH3Hg+ or Cd2+ and antagonistic with that of Ni2+ or Ca2+ has been observed for both the processes of NO3 utilization. The antagonistic interaction of Cu2+ with Hg2+ in terms of NO3 uptake and synergistic with respect to NR activity, has been attributed to the dual bonding preference of Cu2+ for cellular ligands. These findings suggest that (a) a statistically significant correlation exists among such parameters; (b) Hg2+ predominantly attacks the cyanobacterial cell membrane; (c) Hg2+ inhibits NO3 utilization; (d) the presence of other cations increases or decreases the inhibitory actions of Hg2+.  相似文献   

20.
Oscillations in cytoplasmic Ca2+ concentration are a universal mode of signaling following physiological levels of stimulation with agonists that engage the phospholipase C pathway. Sustained cytoplasmic Ca2+ oscillations require replenishment of the membrane phospholipid phosphatidylinositol 4,5-bisphosphate (PIP2), the source of the Ca2+-releasing second messenger inositol trisphosphate. Here we show that cytoplasmic Ca2+ oscillations induced by cysteinyl leukotriene type I receptor activation run down when cells are pretreated with Li+, an inhibitor of inositol monophosphatases that prevents PIP2 resynthesis. In Li+-treated cells, cytoplasmic Ca2+ signals evoked by an agonist were rescued by addition of exogenous inositol or phosphatidylinositol 4-phosphate (PI4P). Knockdown of the phosphatidylinositol 4-phosphate 5 (PIP5) kinases α and γ resulted in rapid loss of the intracellular Ca2+ oscillations and also prevented rescue by PI4P. Knockdown of talin1, a protein that helps regulate PIP5 kinases, accelerated rundown of cytoplasmic Ca2+ oscillations, and these could not be rescued by inositol or PI4P. In Li+-treated cells, recovery of the cytoplasmic Ca2+ oscillations in the presence of inositol or PI4P was suppressed when Ca2+ influx through store-operated Ca2+ channels was inhibited. After rundown of the Ca2+ signals following leukotriene receptor activation, stimulation of P2Y receptors evoked prominent inositol trisphosphate-dependent Ca2+ release. Therefore, leukotriene and P2Y receptors utilize distinct membrane PIP2 pools. Our findings show that store-operated Ca2+ entry is needed to sustain cytoplasmic Ca2+ signaling following leukotriene receptor activation both by refilling the Ca2+ stores and by helping to replenish the PIP2 pool accessible to leukotriene receptors, ostensibly through control of PIP5 kinase activity.  相似文献   

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