共查询到20条相似文献,搜索用时 15 毫秒
1.
The FAD-Enzyme Monodehydroascorbate Radical Reductase Mediates Photoproduction of Superoxide Radicals in Spinach Thylakoid Membranes 总被引:1,自引:0,他引:1
Miyake Chikahiro; Schreiber Ulrich; Hormann Henning; Sano Satoshi; Kozi Asada 《Plant & cell physiology》1998,39(8):821-829
The photoreduction of dioxygen in spinach thylakoid membraneswas enhanced about 10-fold by the FAD-enzyme monodehydroascorbateradical (MDA) reductase at 1 µM. The primary photoreducedproduct of dioxygen catalyzed by MDA reductase was the superoxideradical, as evidenced by the inhibition of photoreduction ofCyt c by superoxide dismutase. The apparent Km for dioxygenof the MDA reductase-dependent photoreduction of dioxygen was100 µM, higher by one order of magnitude than that observedwith thylakoid membranes only. Glutathione reductase, ferredoxin-NADP+reductase, and glycolate oxidase also mediated the photoproductionof superoxide radicals in thylakoid membranes at rates similarto those with MDA reductase. Among these flavoenzymes, MDA reductaseis the most likely mediator stimulating the photoreduction ofdioxygen in chloroplasts; its function in the protection fromphotoinhibition under excess light is discussed. (Received February 24, 1998; Accepted May 19, 1998) 相似文献
2.
Bull R Marengo JJ Finkelstein JP Behrens MI Alvarez O 《American journal of physiology. Cell physiology》2003,285(1):C119-C128
We have reported that ryanodine receptor (RyR) channels display three different responses to cytoplasmic free Ca2+ concentration ([Ca2+]) depending on their redox state (Marengo JJ, Hidalgo C, and Bull R. Biophys J 74: 12631277, 1998), with low, moderate, and high maximal fractional open times (Po). Activation by ATP of single RyR channels from rat brain cortex was tested in planar lipid bilayers with 10 or 0.1 µM cytoplasmic [Ca2+]. At 10 µM [Ca2+], low-Po channels presented lower apparent affinity to activation by ATP [[ATP] for half-maximal activation (KaATP) = 422 µM] than moderate-Po channels (KaATP = 82 µM). Oxidation of low-Po channels with thimerosal or 2,2'-dithiodipyridine (DTDP) gave rise to moderate-Po channels and decreased KaATP from 422 to 82 µM. At 0.1 µM cytoplasmic [Ca2+], ATP induced an almost negligible activation of low-Po channels. After oxidation to high-Po behavior, activation by ATP was markedly increased. Noise analysis of single-channel fluctuations of low-Po channels at 10 µM [Ca2+] plus ATP revealed the presence of subconductance states, suggesting a conduction mechanism that involves four independent subchannels. On oxidation the subchannels opened and closed in a concerted mode. subconductance states; calcium ion release channels; calcium ion regulation; thimerosal; 2,2'-dithiodipyridine 相似文献
3.
Assimilatory nitrate reductase (NR) was solubilized by acetonetreatment from Plectonema boryanum and was purified 7,700-foldby heat treatment, ammonium sulfate fractionation and chromatographyon DEAE-Sephacel and Sephadex G-150. Purified NR had a specificactivity of 85 µmol NO2 formed min1 mg1protein. The enzyme retained both ferredoxin (Fd)- and methylviologen (MV)-linked NR activities throughout the purificationprocedure. Molecular weight was 80,000. The pH optimum was 10.5in the MV-assay and 8.5 when assayed with enzymatically reducedFd as the electron donor. Apparent Km values for nitrate andMV were 700 µM and 2,500µM in the MVassay and 55µM and 75 µM for nitrate and Fd in the Fd-assay.The enzyme was inhibited by thiol reagents and metal-chelatingreagents. (Received October 1, 1982; Accepted March 8, 1983) 相似文献
4.
In a coastal area of southern Chile (41° S), the major ammoniumassimilating enzyme glutamine synthetase (GS) was detected ina green dinoflagellate bloom during April 2003. High chlorophylla concentrations (1000 µg L1) attributable to Gymnodiniumcf. chlorophorum in surface waters were associated with highand very low nitrate reductase activities. Coincident with thebloom, dissolved inorganic nitrogen concentrations were nearthe detection limit (NO3 + NH4+ <0.5 µM). SinceGS correlates with the use of ammonium as an external nitrogensource, we suggest that GS activity seems to be a good indicatorof ammonium utilization in a period dominated by a single dinoflagellatespecies. 相似文献
5.
A study has been made of photosynthetic 14CO2 fixation by isolatedmature internodes of Nitella translucens. Experimentalconditions were similar to those used in studies of the ionicrelations of these cells. Maximum rates of photosynthesis were3340µµmoles CO2, fixed per cm2 of surfacearea per second (equivalent to 1215 /xmoles fixed permg chlorophyll per hour). l4CO2 fixation was inhibited to thedark level by 3(3,4,dichlorophenyl)-1, 1-dimethylurea (at 0-6µM or 10µM) and by the uncoupler carbonyl cyanide-m-chlorophenylhydrazone(SµM). The presence of imidazole or ammonium sulphate(both of which uncouple ATP production in vitro) did not resultin an inhibition of 14CO2 fixation. These results are discussedin relation to published work on solute uptake by Nitella translucens.During photosynthesis there was rapid movement of 14C-labelledorganic compounds out of the chloroplasts. 14C-labelled sucrose,ammo-acids, and sugar phosphates were found in samples of vacuolarsap. 相似文献
6.
We investigated the effects of 5,6-dichloro-1-ethyl-1,3-dihydro-2H-benzimidazol-2-one(DCEBIO) on the Cl secretory response of the mouse jejunum using the Ussing short-circuit current (Isc) technique. DCEBIO stimulated a concentration-dependent, sustained increase in Isc (EC50 41 ± 1 µM). Pretreating tissues with 0.25 µM forskolin reduced the concentration-dependent increase in Isc by DCEBIO and increased the EC50 (53 ± 5 µM). Bumetanide blocked (82 ± 5%) the DCEBIO-stimulated Isc consistent with Cl secretion. DCEBIO was a more potent stimulator of Cl secretion than its parent molecule, 1-ethyl-2-benzimidazolinone. Glibenclamide or NPPB reduced the DCEBIO-stimulated Isc by >80% indicating the participation of CFTR in the DCEBIO-stimulated Isc response. Clotrimazole reduced DCEBIO-stimulated Isc by 67 ± 15%, suggesting the participation of the intermediate conductance Ca2+-activated K+ channel (IKCa) in the DCEBIO-activated Isc response. In the presence of maximum forskolin (10 µM), the DCEBIO response was reduced and biphasic, reaching a peak response of the change in Isc of 43 ± 5 µA/cm2 and then falling to a steady-state response of 17 ± 10 µA/cm2 compared with DCEBIO control tissues (61 ± 6 µA/cm2). The forskolin-stimulated Isc in the presence of DCEBIO was reduced compared with forskolin control tissues. Similar results were observed with DCEBIO and 8-BrcAMP where adenylate cyclase was bypassed. H89, a PKA inhibitor, reduced the DCEBIO-activated Isc, providing evidence that DCEBIO increased Cl secretion via a cAMP/PKA-dependent manner. These data suggest that DCEBIO stimulates Cl secretion of the mouse jejunum and that DCEBIO targets components of the Cl secretory mechanism. 1-ethyl-2-benzimidazolinone; forskolin; glibenclamide; clotrimazole; H89 相似文献
7.
Lin X Jo H Sakakibara Y Tambara K Kim B Komeda M Matsuoka S 《American journal of physiology. Cell physiology》2006,290(2):C601-C608
The effect of -adrenergic stimulation on cardiac Na+/Ca2+ exchange has been controversial. To clarify the effect, we measured Na+/Ca2+ exchange current (INCX) in voltage-clamped guinea pig, mouse, and rat ventricular cells. When INCX was defined as a 5 mM Ni2+-sensitive current in guinea pig ventricular myocytes, 1 µM isoproterenol apparently augmented INCX by 32%. However, this increase was probably due to contamination of the cAMP-dependent Cl current (CFTR-Cl current, ICFTR-Cl), because Ni2+ inhibited the activation of ICFTR-Cl by 1 µM isoproterenol with a half-maximum concentration of 0.5 mM under conditions where INCX was suppressed. Five or ten millimolar Ni2+ did not inhibit ICFTR-Cl activated by 10 µM forskolin, an activator of adenylate cyclase, suggesting that Ni2+ acted upstream of adenylate cyclase in the -adrenergic signaling pathway. Furthermore, in a low-extracellular Cl bath solution, 1 µM isoproterenol did not significantly alter the amplitude of Ni2+-sensitive INCX at +50 mV, which is close to the reversal potential of ICFTR-Cl. No change in INCX amplitude was induced by 10 µM forskolin. When INCX was activated by extracellular Ca2+, it was not significantly affected by 1 µM isoproterenol in guinea pig, mouse, or rat ventricular cells. We concluded that -adrenergic stimulation does not have significant effects on INCX in guinea pig, mouse, or rat ventricular myocytes. cystic fibrosis transmembrane conductance regulator; nickel ion 相似文献
8.
Marine coccolithophorids, Emiliania huxleyi, Gephyrocapsa oceanicaand Helladosphaera sp. were found to require selenium for theirgrowth. The optimum concen trations were 110 nM for SeO2and SeO32 and above 1 µM for SeO24 Duringthe depletion of selenium algal growth was strongly suppressedaccompanied with the decrease in net photosynthesis. (Received November 18, 1998; Accepted April 16, 1999) 相似文献
9.
A Comparison between the Uptake of Potassium by Plants from Solutions of Constant Potassium Concentration and during Depletion 总被引:6,自引:0,他引:6
A comparison was made between two methods of measuring the relationshipbetween the external [K+] and the flux of K+ into whole plantsof Lolium perenne and Raphanus sativus. The values of flux obtainedfrom solutions of 1.2 µM K+ held constant around the rootswere three and six times greater for Lolium and Raphanus respectivelythan the values obtained at the same concentration in a depletionexperiment in which the solutions, initially 100 µM K+,were depleted to below 1.2 µM K+ by plant uptake. In thedepletion experiment with Lolium, the flux was higher into plantsgrown at low [K+] than into plants grown at 100 µM eventhough [K+] within the plant was about the same for all groupsof plants. It is suggested that Lolium grown at low [K+] hasan efficient mechanism for K+ uptake which continues to operatefor some time after the plants have been transferred to a higherconcentration. With both species, Km was 1520 µMin the depletion experiment and below 1 µM when concentrationswere held constant. 相似文献
10.
Effects of simulated acid rain and heavy metal deposition onthe ultrastructure of the lichenBryoria fuscescens(Gyeln.) Brodoand Hawksw. were examined in a field study conducted in northernFinland. Lichens were exposed to simulated rain containing twolevels of a mixture of copper (Cu2+) and nickel (Ni2+) ionsalone or in combination with acid rain (H2SO4) at pH 3 over2 months in addition to ambient rainfall. The algal and fungalcomponents responded differently to pH and there was an interactionwith metal toxicity. The algal partner was the most sensitiveto acid rain and heavy metal combinations and had more degeneratecells than the fungal partner. Damage was apparent in chloroplastsand mitochondria, where thylakoid and mitochondrial cristaewere swollen. The fungal partner was the more sensitive to highconcentrations of metal ions in the absence of acidity, suggestingan ameliorating interaction between the metals and acidity.For algae, critical metal concentrations in the thallus were>50 µg g-1for Cu and >7 µg g-1for Ni in thepresence of acidity, and >20 µ g g-1for Ni in the absenceof acidity. Detrimental effects of heavy metals on fungal ultrastructurewere seen when thallus metal concentrations exceeded 400 µgg-1for Cu and 100 µg g-1d. wt for Ni. The results suggestthat acid wet deposition containing metal ions may reduce survivalof lichens in northern environments.Copyright 1998 Annals ofBotany Company. Copper, nickel, sulphuric acid, ultrastructure,Bryoria fuscescens(Gyeln.) Brodo and Hawksw., epiphytic lichen, air pollution. 相似文献
11.
Induction of the H+ Release from Thylakoid Membranes by Illumination in the Presence of Protonophores at High Concentrations 总被引:1,自引:0,他引:1
Yamasaki Hideo; Furuya Shigeki; Kawamura Akira; Ito Akio; Okayama Shigeki; Nishimura Mitsuo 《Plant & cell physiology》1991,32(7):925-934
The generally observed light-induced uptake of protons intothe thylakoid lumen is diminished by adding protonophores. Insteadof the H+ uptake, the release of protons was observed duringillumination in the presence of various protonophores at highconcentrations, namely, 1 µM nigericin, 10 µM carbonylcyanidem-chlorophenylhydrazone or 30 µM gramicidin. An uncoupler,NH4C1 (4 mM), and a detergent, Triton X-100 (0.02%), also inducedthe H+ release but a K+ ionophore, valinomycin, did not. Theamount of H+ released reached about 100 nmol H+ (mg Chl)1at pH 7.5 under continuous illumination. The rate of the H+release was similar to that of the conventional H+ uptake butits dark relaxation was much slower than that of the H+ uptake.We compared the H+ release in protonophore-added thylakoidswith the previously reported H+ release in coupling factor 1(CF1-depleted thylakoids. The H+ release in thylakoids withnigericin showed similar characteristics to that in CF1-depletedthylakoids in terms of their responses to pH, phenazine methosulfateand light intensity. Both types of H+ release were relativelyinsensitive to DCMU and were stimulated somewhat by DCMU atlow concentrations (around 200 nM). Nigericin did not inhibitthe superoxide dismutase activity of the membranes. These resultsindicate that the H+ release in protonophore-added thylakoidsand that in CF1 depleted thylakoids involve the same mechanismand that water-derived protons from PS II that result from animpairment of the activity of superoxide dismutase, as previouslyproposed, are not involved. Judging from the rate of electronflow and the lumenal acidification under the illumination, weconclude that the H+ release is a light-dependent scalar processwhich can be observed in thylakoid membranes with high H+ permeability.The H+ release of this type was not observed in mitochondriafrom rat liver or in chromatophores from Rhodobacter sphaeroides. (Received November 29, 1990; Accepted June 27, 1991) 相似文献
12.
Properties of the nucleotide binding sites on chloroplast couplingfactor 1 (CF1) were studied by equilibrium dialysis and UV spectroscopy.From our direct binding studies, we identified at least fourkinds of ADP binding sites on CF1; a barely dissociable ADPbinding site (site A), a slowly exchangeable high affinity sitewith dissociation constant (Kd) 0.021 µM (site B), anotherslowly exchangeable high affinity site with Kd 1.6 µM(site C) and several low affinity (Kd {small tilde}30 µM)sites. The Kd values for sites B and C of the other nucleotidestested were 0.5 µM and 16 µM (GDP), 8 µM and34 µM (CDP), 17 µM and 20 µM (UDP) and 1.4µM and 1.4 µM (PP1). From a comparison of the observed UV spectral change and theamount of nucleotide bound to these sites, as calculated fromthe above Kd values, we concluded that the nucleotide bindingto site B or G induces UV spectral changes that are almost thesame in shape and magnitude. The estimated difference molarabsorption coefficient () was 3.4?103M1ADP cm1for ADP at 278 nm. Our conclusions were strengthened by thegood agreement between the observed spectra and the calculatedspectra (derived from the Kd and values of ADP and GDP) whenADP and GDP were added together to CF1. The cause of the unusual behavior of GDP in the UV differencespectrum which was unexplained in our previous report was shownto be competition between the GDP added and previously boundADP at sites B and C; this distorted the real spectrum inducedby GDP. (Received October 3, 1983; Accepted February 13, 1984) 相似文献
13.
Fioretti B Pietrangelo T Catacuzzeno L Franciolini F 《American journal of physiology. Cell physiology》2005,289(1):C89-C96
We report here the expression in C2C12 myoblasts of the intermediate-conductance Ca2+-activated K+ (IKCa) channel. The IKCa current, recorded under perforated-patch configuration, had a transient time course when activated by ionomycin (0.5 µM; peak current density 26.2 ± 3.7 pA/pF; n = 10), but ionomycin (0.5 µM) + 5,6-dichloro-1-ethyl-1,3-dihydro-2H-benzimidazol-2-one (100 µM) evoked a stable outward current (28.4 ± 8.2 pA/pF; n = 11). The current was fully inhibited by charybdotoxin (200 nM), clotrimazole (2 µM), and 5-nitro-2-(3-phenylpropylamino)benzoic acid (300 µM), but not by tetraethylammonium (1 mM) or D-tubocurarine (300 µM). Congruent with the IKCa channel, elevation of intracellular Ca2+ in inside-out patches resulted in the activation of a voltage-insensitive K+ channel with weak inward rectification, a unitary conductance of 38 ± 6 pS (at negative voltages), and an IC50 for Ca2+ of 530 nM. The IKCa channel was activated metabotropically by external application of ATP (100 µM), an intracellular Ca2+ mobilizer. Under current-clamp conditions, ATP application resulted in a membrane hyperpolarization of 35 mV. The IKCa current downregulated during myogenesis, ceasing to be detectable 4 days after the myoblasts were placed in differentiating medium. Downregulation was prevented by the myogenic suppressor agent basic FGF (bFGF). We also found that block of the IKCa channel by charybdotoxin did not inhibit bFGF-sustained myoblast proliferation. These observations show that in C2C12 myoblasts the IKCa channel expression correlates inversely with differentiation, yet it does not appear to have a role in myoblast proliferation. ATP; cell proliferation 相似文献
14.
A His-tagged PSII core complex was purified from recombinantChlamydomonas reinhardtii D2-H thylakoids by single-step Ni2+-affinitycolumn chromatography and its properties were partially characterizedin terms of their PSII functions and chemical compositions.The PSII core complex that has a His-tag extension at the C-terminusof the D2 protein evolved oxygen at a high rate of 2,400 µmol(mg Chl)1h1 at the optimum pH of 6.5 with ferricyanideand 2,6-dichlorobenzoquinone as electron acceptors in the presenceof Ca2+ as an essential cofactor, and approximately 90% of theactivity was blocked by 10 µM DCMU. The core complex exhibitedthe thermoluminescence Q-band but not the B-band regardlessof the presence or absence of DCMU, although both bands wereobserved in the His-tagged thylakoids. The core complex wasfree from PSI and contained one YD, Tyr 160 of the D2 protein,four Mn atoms, two cytochrome b-559, about 46 Chl a molecules,and probably one QA, the primary acceptor quinone of PSII. Itwas inferred from these results that His-tagging at the C-terminusof the D2 protein does not affect the functional and structuralintegrity of the PSII core complex, and that the His-tagstrategy is highly useful for biochemical, physicochemical,and structural studies of Chlamydomonas PSII. (Received October 22, 1998; Accepted December 25, 1998) 相似文献
15.
Fatty acid metabolites accumulate in the heart underpathophysiological conditions that affect -oxidation and can elicit marked electrophysiological changes that are arrhythmogenic. The purpose of the present study was to determine the impact of amphiphilic fatty acid metabolites on K+currents that control cardiac refractoriness and excitability. Transient outward(Ito) andinward rectifier(IK1)K+ currents were recorded by thewhole cell voltage-clamp technique in rat ventricular myocytes, and theeffects of two major fatty acid metabolites were examined:palmitoylcarnitine and palmitoyl-coenzyme A (palmitoyl-CoA).Palmitoylcarnitine (0.5-10 µM) caused a concentration-dependent decrease in Itodensity in myocytes internally dialyzed with the amphiphile; 10 µMreduced mean Itodensity at +60 mV by 62% compared with control(P < 0.05). In contrast, externalpalmitoylcarnitine at the same concentrations had no effect, nor didinternal dialysis significantly alterIK1. Dialysiswith palmitoyl-CoA (1-10 µM) produced a smaller decrease inIto densitycompared with that produced by palmitoylcarnitine; 10 µM reduced meanIto density at+60 mV by 37% compared with control(P < 0.05). Both metabolites delayedrecovery of Itofrom inactivation but did not affect voltage-dependent properties.Moreover, the effects of palmitoylcarnitine were relatively specific,as neither palmitate (10 µM) nor carnitine (10 µM) alone significantly influencedIto when added tothe pipette solution. These data therefore suggest that amphiphilicfatty acid metabolites downregulateIto channels by amechanism confined to the cytoplasmic side of the membrane. Thisdecrease in cardiac K+ channelactivity may delay repolarization under pathophysiological conditionsin which amphiphile accumulation is postulated to occur, such asdiabetes mellitus or myocardial infarction. 相似文献
16.
Photosynthetic Carbon Sources of Stream Macrophytes 总被引:15,自引:0,他引:15
Rates of photosynthesis of four submerged stream macrophyteswere examined under varying pH and composition of inorganiccarbon species. Callitriche stagnatis and Sparganium simplexused only CO2 for photosynthesis. Potamogeton crispus and P.pectinatus used HCO3 in addition to CO2, but with much lowerefficiency. The photosynthetic rates at air equilibrium anda total inorganic carbon concentration of 5.0 mM were 23times lower than maximum rates at CO2 saturation for the HCO3users and 1014 times lower for the CO2 users. The CO2compensation point of entire plants of Callitriche (2.5 µM)and Sparganium (6.0µM) was well below the equilibriumconcentration (15 µM). and the low saturation points (250500µM) also pointed to efficient use of CO2. Callitricheand Sparganium compete successfully with HCO3 users inhardwater streams, which have a higher exchange and generationcapacity of CO2 than stagnant and more soft waters. Rates ofphotosynthesis of Potamogeton crispus and P. pectinatus decreasedat high pH. Depending on the two alternative hypotheses forHCO3use, this decline can be explained by CO3inhibition of HCO3 uptake or by increasing capacity tobuffer H+efflux from the plant. Habitats subject to high pH,e. g. small ponds with dense vegetation, may have a strong selectionfor efficient mechanisms of HCO3 use. Key words: Photosynthesis, Macrophytes, Carbon-source 相似文献
17.
A Cyt P450 (P450C4H) possessing trans-cinnamate 4-hydroxylase(C4H) activity was purified to apparent homogeneity from microsomesof etiolated mung bean seedlings. Upon SDS-polyacrylamide gelelectrophoresis, the purified preparation gave a single proteinband with a molecular mass of 58-kDa. Its specific P450 contentwas 12.6 nmol (mg protein)1. Using NADPH as electrondonor, purified P450C4H aerobically converted trans-cinnamicacid to p-coumaric acid with a specific activity of 68 nmolmin1 nmol1 P450 in a reconstituted system containingNADPH-Cyt P450 reductase purified from the seedlings or rabbitliver microsomes, dilauroyl phosphatidylcholine, and cholate.This specific activity is by far the highest for reconstitutedC4H systems so far reported and provides direct evidence thatC4H activity is actually associated with a P450 protein. Inthe oxidized state P450C4H showed a typical low-spin type absorptionspectrum with a Soret peak at 419 nm. A partial spectral shiftto the high spin state was observed when trans-cinnamic acidwas added to oxidized P450C4H. By spectral titration, the dissociationconstant of the cinnamic acid-P450C4H complex was determinedto be 2.8 µM. This value is similar to the Km value (1.8µM) for trans-cinnamic acid determined in the reconstitutedsystem. (Received November 20, 1992; Accepted February 17, 1993) 相似文献
18.
Bahadi R Farrelly PV Kenna BL Curtain CC Masters CL Cappai R Barnham KJ Kourie JI 《American journal of physiology. Cell physiology》2003,285(4):C873-C880
We found that the amyloid peptide A(1-42) is capable of interacting with membrane and forming heterogeneous ion channels in the absence of any added Cu2+ or biological redox agents that have been reported to mediate A(1-42) toxicity. The A(1-42)-formed cation channel was inhibited by Cu2+ in cis solution ([Cu2+]cis) in a voltage- and concentration-dependent manner between 0 and 250 µM. The [Cu2+]cis-induced channel inhibition is fully reversible at low concentrations between 50 and 100 µM [Cu2+]cis and partially reversible at 250 µM [Cu2+]cis. The inhibitory effects of [Cu2+]cis between 50 and 250 µM on the channel could not be reversed with addition of Cu2+-chelating agent clioquinol (CQ) at concentrations between 64 and 384 µM applied to the cis chamber. The effects of 200-250 µM [Cu2+]cis on the burst and intraburst kinetic parameters were not fully reversible with either wash or 128 µM [CQ]cis. The kinetic analysis of the data indicate that Cu2+-induced inhibition was mediated via both desensitization and an open channel block mechanism and that Cu2+ binds to the histidine residues located at the mouth of the channel. It is proposed that the Cu2+-binding site of the A(1-42)-formed channels is modulated with Cu2+ in a similar way to those of channels formed with the prion protein fragment PrP(106-126), suggesting a possible common mechanism for Cu2+ modulation of A and PrP channel proteins linked to neurodegenerative diseases. neurodegenerative diseases; transitional metals; ion channel pathologies; membrane injuries; calcium homeostasis 相似文献
19.
In "air-grown" Chroomonas sp. cells, low concentrations of DCMU(less than 0.1 µM) could prevent the inhibition of 14CO2fixation by anaerobiosis under light-saturating conditions (morethan 40 W.m2), with phenazine methosulfate showing asimilar effect. Antimycin A, carbonyl cyanide m-chlorophenylhydrazone(CCCP), and N,N'-dicyclohexylcarbodiimide strongly inhibitedanaerobic photosynthesis at concentrations which did not significantlyinhibit the rate under 2% O2 at high light intensity (200 W.m2),although 0.2 µM CCCP stimulated the rate under 2% O2 tosome extent. On the other hand, KCN inhibited the rate muchmore strongly under 2% O2 than N2, although it inhibited therate very strongly at concentrations above 5 µM both underN2 and 2% O2. These results suggest that the inhibition of photosynthetic14CO2 fixation by anaerobiosis in this alga result from ATPdeficiency caused by over-reduction of electron carriers ofthe cyclic electron flow and that oxygen can prevent the over-reduction.Cyclic electron flow seems to be necessary to provide additionalATP for CO2 reduction under anaerobic conditions, although itseems to be less necessary under aerobic conditions. (Received July 21, 1983; Accepted January 23, 1984) 相似文献
20.
p38 mitogen-activated protein kinase inhibits calcium-dependent chloride secretion in T84 colonic epithelial cells 总被引:1,自引:0,他引:1
We havepreviously shown that Ca2+-dependent Clsecretion across intestinal epithelial cells is limited by a signalingpathway involving transactivation of the epidermal growth factorreceptor (EGFR) and activation of ERK mitogen-activated protein kinase (MAPK). Here, we have investigated a possible role for p38 MAPK inregulation of Ca2+-dependent Cl secretion.Western blot analysis of T84 colonic epithelial cells revealed that the muscarinic agonist carbachol (CCh; 100 µM)stimulated phosphorylation and activation of p38 MAPK. The p38inhibitor SB-203580 (10 µM) potentiated and prolonged short-circuitcurrent (Isc) responses to CCh acrossvoltage-clamped T84 cells to 157.4 ± 6.9% of thosein control cells (n = 21; P < 0.001).CCh-induced p38 phosphorylation was attenuated by the EGFR inhibitortyrphostin AG-1478 (0.1 nM-10 µM) and by the Src family kinaseinhibitor PP2 (20 nM-2 µM). The effects of CCh on p38phosphorylation were mimicked by thapsigargin (TG; 2 µM), whichspecifically elevates intracellular Ca2+, and wereabolished by the Ca2+ chelator BAPTA-AM (20 µM), implyinga role for intracellular Ca2+ in mediating p38 activation.SB-203580 (10 µM) potentiated Isc responses toTG to 172.4 ± 18.1% of those in control cells (n = 18; P < 0.001). When cells were pretreated withSB-203580 and PD-98059 to simultaneously inhibit p38 and ERK MAPKs,respectively, Isc responses to TG and CCh weresignificantly greater than those observed with either inhibitor alone.We conclude that Ca2+-dependent agonists stimulate p38 MAPKin T84 cells by a mechanism involving intracellularCa2+, Src family kinases, and the EGFR. CCh-stimulated p38activation constitutes a similar, but distinct and complementary,antisecretory signaling pathway to that of ERK MAPK. 相似文献