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1.
Originally published in Annals of Botany84: 639–644 1999.For technical reasons beyond our control the flux symbol wasomitted from this paper. The paper is reprinted here in itsentirety. Short term experiments investigated the effects of potassiumsupply on radiocaesium influx/efflux and the radiocaesium compartmentationin intact spring wheat roots. Short term (24–72 h) influxanalysis showed that net influxes of radiocaesium to both rootand xylem were reduced approximately ten-times by increasingexternal potassium concentration from 50 µM to 200 µM.Efflux analysis distinguished three components for radiocaesium(namely cell wall+free space, cytoplasm and vacuole) and showedthat the rates of Cs+efflux at an external potassium concentrationof 100 µM (19.16 and 1.70 Bq g-1min-1for coand vo, respectively)were about three-times faster than those at 50 µM (7.24and to 0.41 Bq g-1min-1for coand vo, respectively). The resultsalso showed that external potassium concentration did not havea significant effect on the distribution of137Cs between cytoplasmand vacuole, as indicated by the ratio of137Cs in the two compartments.Results obtained in this study suggested that the inhibitoryeffect of potassium on the net uptake of radiocaesium by theplant root may be partially ascribed to the fact that at higherexternal potassium concentrations Cs+efflux rates were muchhigher. The mechanisms involved are discussed. Copyright 2000Annals of Botany Company Compartmentation, efflux analysis, potassium, radiocaesium, Triticum aestivum, wheat.  相似文献   

2.
Extracellular ATP stimulates volume decrease in Necturus red blood cells   总被引:2,自引:0,他引:2  
This study examined whether extracellular ATP stimulatesregulatory volume decrease (RVD) in Necturusmaculosus (mudpuppy) red blood cells (RBCs). Thehemolytic index (a measure of osmotic fragility) decreased withextracellular ATP (50 µM). In contrast, the ATP scavenger hexokinase(2.5 U/ml, 1 mM glucose) increased osmotic fragility. In addition, theATP-dependent K+ channelantagonist glibenclamide (100 µM) increased the hemolytic index, andthis inhibition was reversed with ATP (50 µM). We also measured cellvolume recovery in response to hypotonic shock electronically with aCoulter counter. Extracellular ATP (50 µM) enhanced cell volumedecrease in a hypotonic (0.5×) Ringer solution. In contrast, hexokinase (2.5 U/ml) and apyrase (an ATP diphosphohydrolase, 2.5 U/ml)inhibited cell volume recovery. The inhibitory effect of hexokinase wasreversed with the Ca2+ ionophoreA-23187 (1 µM); it also was reversed with the cationophore gramicidin(5 µM in a choline-Ringer solution), indicating that ATP was linkedto K+ efflux. In addition,glibenclamide (100 µM) and gadolinium (10 µM) inhibited cell volumedecrease, and the effect of these agents was reversed with ATP (50 µM) and A-23187 (1 µM). Using the whole cell patch-clamp technique,we found that ATP (50 µM) stimulated a whole cell current underisosmotic conditions. In addition, apyrase (2.5 U/ml), glibenclamide(100 µM), and gadolinium (10 µM) inhibited whole cell currents thatwere activated during hypotonic swelling. The inhibitory effect ofapyrase was reversed with the nonhydrolyzable analog adenosine5'-O-(3-thiotriphosphate) (50 µM), and the effect of glibenclamide or gadolinium was reversed withATP (50 µM). Finally, anionic whole cell currents were activated withhypotonic swelling when ATP was the only significant charge carrier,suggesting that increases in cell volume led to ATP efflux through aconductive pathway. Taken together, these results indicate thatextracellular ATP stimulated cell volume decrease via aCa2+-dependent step that led toK+ efflux.

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3.
Auxin Stimulates Cl-Uptake by Oat Coleoptiles   总被引:1,自引:0,他引:1  
The effects of auxin on net ion fluxes near parenchyma of oatcoleoptiles were studied using the non-invasive MIFE systemto measure specific ion fluxes using ion selective microelectrodes.Application of 10 µM1-naphthaleneacetic acid (NAA) for3 h caused doubling of coleoptile segment growth, without changingthe pH of the unbuffered bathing solution from pH 5.4 duringthat time. Short term experiments revealed that auxin led toan immediate three-fold increase of chloride influx to 1200nmol m-2s-1, maintained for at least 1 h. In the first minutesafter auxin application, proton fluxes were small (-25 nmolm-2s-1, an efflux) and tended to decrease, whereas potassiumand calcium fluxes changed little, fluctuating from -100 to0 nmol m-2s-1and from -15 to 0 nmol m-2s-1, respectively. Itis suggested that one target of auxin action in plant cellsis the plasma membrane chloride transport system mediating increasedchloride uptake.Copyright 1998 Annals of Botany Company Auxin, chloride transport, ion flux,Avena sativaL., oat.  相似文献   

4.
Stretch-induced Ca(2+) release via an IP(3)-insensitive Ca(2+) channel   总被引:6,自引:0,他引:6  
Various mechanicalstimuli increase the intracellular Ca2+ concentration([Ca2+]i) in vascular smooth muscle cells(VSMC). A part of the increase in [Ca2+]i isdue to the release of Ca2+ from intracellular stores. Wehave investigated the effect of mechanical stimulation produced bycyclical stretch on the release of Ca2+ from theintracellular stores. Permeabilized VSMC loaded with 45Ca2+ were subjected to 7.5% average (15%maximal) cyclical stretch. This resulted in an increase in45Ca2+ rate constant by 0.126 ± 0.0035. Inhibition of inositol 1,4,5-trisphosphate (IP3),ryanodine, and nicotinic acid adenine dinucleotide phosphate channels(NAADP) with 50 µg/ml heparin, 50 µM ruthenium red, and 25 µMthio-NADP, respectively, did not block the increase in45Ca2+ efflux in response to cyclical stretch.However, 10 µM lanthanum, 10 µM gadolinium, and 10 µMcytochalasin D but not 10 µM nocodazole inhibited the increase in45Ca2+ efflux. This supports the existence of anovel stretch-sensitive intracellular Ca2+ store in VSMCthat is distinct from the IP3-, ryanodine-, and NAADP-sensitive stores.

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5.
The mechanism of the Ca2+-dependent Cl efflux was studiedin tonoplast-free cells, in which the intracellular chemicalcomposition can be freely controlled. Tonoplast-free cells wereprepared by perfusing the cell interior of internodal cellsof Chara corallina with a medium that contained EGTA. The Ca2+-inducedCl efflux was measured together with the membrane potentialduring continuous intracellular perfusion. The dependenciesof Cl efflux and the membrane potential on the intracellularCa2+ or Cl concentrations were analyzed. When perfusionwas started with medium that contained Ca2+ ions, Clefflux and membrane depolarization were induced. The amountof Cl efflux varied considerably among individual cells.The rate of efflux decreased exponentially but a residual effluxremained detectable. The Cl efflux was induced at concentrationsof Ca2+ ions above 1 µM and reached a maximum at 1 mM.By contrast, the membrane depolarization reached a maximum atabout 10 µM Ca2+. The rate of Cl efflux increasedlinearly with logarithmic increases in the intracellular Clconcentrations. These findings suggest that more than two kindsof Ca2+-dependent Cl channel might be present in theplasma membrane. Addition of ATP or its removal from the perfusion medium didnot affect the Ca2+-dependent Cl efflux. Calmodulin antagonistsslightly inhibited the Ca2+-dependent Cl efflux. 1Present address: Biological Laboratory, Hitotsubashi University,Naka 2-1, Kunitachi, Tokyo, 186 Japan.  相似文献   

6.
White  P. J. 《Annals of botany》1993,72(4):349-358
The development and growth of rye (Secale cereale L. cv. Rheidol)was studied in seedlings grown hydroponically in complete nutrientsolutions containing between 10 and 600 µM K+. The phyllochron(defined as the interval between the appearance of successiveleaves) was used as a developmental timescale to compare plants.The pattern of both shoot and root development was strictlyordered on a phyllochron basis and was unaffected by solutionK+ concentration, with the exception that tillers in plantsgrown at the lowest K+ concentrations were occasionally eithernot initiated or aborted at an early stage of development. However,both the rate of leaf appearance on the main stem and successivetillers and the rate of tiller appearance were slower in plantsgrown at lower K+ concentrations. The rate of leaf appearanceon the main stem was reduced to below 90% of its maximal valueat solution concentrations below about 50 µM K+. Plantrelative growth rate (RGR) was also reduced by lowering theK+ concentration of the nutrient solution and fell to below90% of its maximal value at solution concentrations below about200 µM K+. There was a complex relationship between tissueK+ concentration and the K+ concentration of the nutrient solution,which differed between leaves and root. Leaf K+ concentrationincreased steadily from about 50 µmol g-1 f. wt to about200 µmol g-1 f. wt as solution K+ concentration was increasedfrom 10 to 400 µM. In contrast, root K+ concentrationexhibited a sigmoidal dependence on solution K+ concentration,maintaining a minimal value of approximately 20 µmol g-1f. wt at concentration below 100 µM K+, then increasingprogressively to about 120 µmol g-1 f. wt at a solutionconcentration of 600 µM K+. The 'critical' leaf K+ concentration,i.e. the concentration at which either plant RGR or plant developmentwas reduced 90% of its maximal value, was 86 µmol g-1f. wt for plant RGR and 150 µmol g-1 f. wt for plant development.The 'critical' root K+ concentration was 24 µmol g-1 f.wt K+ for both RGR and development. A decline in tissue K+ concentrationbelow these thresholds reduced plant growth considerably. RootK+ concentration was a sensitive indicator of the K+ statusof the plant with respect to potential growth since plant growthdeclined abruptly as root K+ concentration approached its 'critical'value, whereas plant growth showed a less defined relationshipwith shoot K+ concentration.Copyright 1993, 1999 Academic Press Critical K+ concentration, development, potassium, relative growth rate (RGR), rye, Secale cereale L. cv. Rheidol  相似文献   

7.
In fura 2-loaded N1E-115 cells, regulationof intracellular Ca2+ concentration([Ca2+]i) following a Ca2+ loadinduced by 1 µM thapsigargin and 10 µM carbonylcyanidep-trifluoromethyoxyphenylhydrazone (FCCP) wasNa+ dependent and inhibited by 5 mM Ni2+. Incells with normal intracellular Na+ concentration([Na+]i), removal of bath Na+,which should result in reversal of Na+/Ca2+exchange, did not increase [Ca2+]i unlesscell Ca2+ buffer capacity was reduced. When N1E-115 cellswere Na+ loaded using 100 µM veratridine and 4 µg/mlscorpion venom, the rate of the reverse mode of theNa+/Ca2+ exchanger was apparently enhanced,since an ~4- to 6-fold increase in [Ca2+]ioccurred despite normal cell Ca2+ buffering. In SBFI-loadedcells, we were able to demonstrate forward operation of theNa+/Ca2+ exchanger (net efflux ofCa2+) by observing increases (~ 6 mM) in[Na+]i. These Ni2+ (5 mM)-inhibited increases in [Na+]i could onlybe observed when a continuous ionomycin-induced influx ofCa2+ occurred. The voltage-sensitive dyebis-(1,3-diethylthiobarbituric acid) trimethine oxonol was used tomeasure changes in membrane potential. Ionomycin (1 µM) depolarizedN1E-115 cells (~25 mV). This depolarization was Na+dependent and blocked by 5 mM Ni2+ and 250-500 µMbenzamil. These data provide evidence for the presence of anelectrogenic Na+/Ca2+ exchanger that is capableof regulating [Ca2+]i after release ofCa2+ from cell stores.

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8.
K+ efflux from tobacco (Nicotiana tabacum L, cv. Samsun NN)leaf discs into the external medium was increased and the membranepotential (Em) changed in the positive direction with a changein pH from 8.0 to 4.0. Em was affected by the external concentrationof KCl, greatly decreasing with a change in concentration from1 mM to 100 mM. The equilibrium potential of the membrane forK+ (Ek) was decreased in a Nernst fashion with increasing externalconcentrations of KCl. Ek is more positive than Em above ca.50 µM KCl. Most of the experiments were carried out underconditions in which the difference between the electrochemicalpotential for K+ on the inside to the outside of the cell (µkis positive. Thus, K+ may passively flow to the outside of thecells accompanied by the depolarization of the membrane. Abscisic acid (ABA) increased the K+ efflux under conditionsof passive transport. K+ efflux was accelerated with an increasingconcentration of ABA, being maximal at 10–4 M–10–3M. This acceleration was due to the enhancement of the potassiummotive force (µk/F) which is the force causing the netpassive transport of K+. The membrane potential was decreasedfrom –205 mV to –170 mV by 2 x 10–4 M ABAwithin 10 min. The depolarization was not transient, being lostfor at least 3 hr. These results show that ABA accelerated passive K+ efflux, whichaccompanied depolarization of the membrane. (Received June 22, 1981; Accepted August 24, 1981)  相似文献   

9.
This paper examines the ionic composition of wound-induced electricalcurrents in higher plant tissue, using two non-injurious electrophysiologicaltechniques. By simultaneous recording of K+, H+ , and Ca2+ ionfluxes with extracellular ion-selective microelectrodes, wehave determined that a Ca2+ influx (2.4 µA cm–2),a small H+ influx (0.17 µA cm–2) and a large K+efflux (16 µA cm–2) occur immediately after woundingin roots of Pisum sativum L. var. Greenfeast. Using an extracellularvibrating probe at the wound site, net ion currents of 26 µAcm–2 were measured 5 min after wounding. In a more concentratedbathing medium (1/4 rather than 1/16 strength Hoagland's solution),net ion currents of 59 µA cm–2 were measured, andthese would appear to be the largest extracellular currentsthat have been measured in plants. We made a quantitative comparisonof the summed ion fluxes with the net ion currents and thisrevealed that ion fluxes, in addition to those measured here,occur after wounding. Key words: Wounding, ion flux, electric current, calcium, potassium  相似文献   

10.
In the present study, we used laser scanning confocal microscopy in combination with fluorescent indicator dyes to investigate the effects of nitric oxide (NO) produced endogenously by stimulation of the mitochondria-specific NO synthase (mtNOS) or applied exogenously through a NO donor, on mitochondrial Ca2+ uptake, membrane potential, and gating of mitochondrial permeability transition pore (PTP) in permeabilized cultured calf pulmonary artery endothelial (CPAE) cells. Higher concentrations (100–500 µM) of the NO donor spermine NONOate (Sper/NO) significantly reduced mitochondrial Ca2+ uptake and Ca2+ extrusion rates, whereas low concentrations of Sper/NO (<100 µM) had no effect on mitochondrial Ca2+ levels ([Ca2+]mt). Stimulation of mitochondrial NO production by incubating cells with 1 mM L-arginine also decreased mitochondrial Ca2+ uptake, whereas inhibition of mtNOS with 10 µM L-N5-(1-iminoethyl)ornithine resulted in a significant increase of [Ca2+]mt. Sper/NO application caused a dose-dependent sustained mitochondrial depolarization as revealed with the voltage-sensitive dye tetramethylrhodamine ethyl ester (TMRE). Blocking mtNOS hyperpolarized basal mitochondrial membrane potential and partially prevented Ca2+-induced decrease in TMRE fluorescence. Higher concentrations of Sper/NO (100–500 µM) induced PTP opening, whereas lower concentrations (<100 µM) had no effect. The data demonstrate that in calf pulmonary artery endothelial cells, stimulation of mitochondrial Ca2+ uptake can activate NO production in mitochondria that in turn can modulate mitochondrial Ca2+ uptake and efflux, demonstrating a negative feedback regulation. This mechanism may be particularly important to protect against mitochondrial Ca2+ overload under pathological conditions where cellular [NO] can reach very high levels. nitric oxide synthase; permeability transition pore; endothelium  相似文献   

11.
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 min–1 mg–1protein. 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   

12.
Hypotonicswelling increases the intracellular Ca2+ concentration([Ca2+]i) in vascular smooth muscle cells(VSMC). The source of this Ca2+ is not clear. To study thesource of increase in [Ca2+]i in response tohypotonic swelling, we measured [Ca2+]i infura 2-loaded cultured VSMC (A7r5 cells). Hypotonic swelling produced a40.7-nM increase in [Ca2+]i that was notinhibited by EGTA but was inhibited by 1 µM thapsigargin. Priordepletion of inositol 1,4,5-trisphosphate (IP3)-sensitive Ca2+ stores with vasopressin did not inhibit the increasein [Ca2+]i in response to hypotonic swelling.Exposure of 45Ca2+-loaded intracellular storesto hypotonic swelling in permeabilized VSMC produced an increase in45Ca2+ efflux, which was inhibited by 1 µMthapsigargin but not by 50 µg/ml heparin, 50 µM ruthenium red, or25 µM thio-NADP. Thus hypotonic swelling of VSMC causes a release ofCa2+ from the intracellular stores from a novel sitedistinct from the IP3-, ryanodine-, and nicotinic acidadenine dinucleotide phosphate-sensitive stores.

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13.
Ascorbate has previously been shown to enhance both 1- and 2-adrenergic activity. This activity is mediated by ascorbate binding to the extracellular domain of the adrenergic receptor, which also decreases the oxidation rate of ascorbate. H1 histamine receptors have extracellular agonist or ascorbate binding sites with strong similarities to 1- and 2-adrenergic receptors. Physiological concentrations of ascorbate (50 µM) significantly enhanced histamine contractions of rabbit aorta on the lower half of the histamine dose-response curve, increasing contractions of 0.1, 0.2, and 0.3 µM histamine by two- to threefold. Increases in ascorbate concentration significantly enhanced 0.2 µM histamine (5–500 µM ascorbate) and 0.3 µM histamine (15–500 µM ascorbate) in a dose-dependent manner. Histamine does not measurably oxidize over 20 h in oxygenated PSS at 37°C. Thus the ascorbate enhancement is independent of ascorbate's antioxidant effects. Ascorbate in solution oxidizes rapidly. Transfected histamine receptor membrane suspension with protein concentration at >3.1 µg/ml (56 nM maximum histamine receptor) decreases the oxidation rate of 392 µM ascorbate, and virtually no ascorbate oxidation occurs at >0.0004 mol histamine receptor/mol ascorbate. Histamine receptor membrane had an initial ascorbate oxidation inhibition rate of 0.094 min·µg protein–1·ml–1, compared with rates for transfected ANG II membrane (0.055 min·µg protein–1·ml–1), untransfected membrane (0.052 min·µg protein–1·ml–1), creatine kinase (0.0082 min·µg protein–1·ml–1), keyhole limpet hemocyanin (0.00092 min·µg protein–1·ml–1), and osmotically lysed aortic rings (0.00057 min·µg wet weight–1·ml–1). Ascorbate enhancement of seven-transmembrane-spanning membrane receptor activity occurs in both adrenergic and histaminergic receptors. These receptors may play a significant role in maintaining extracellular ascorbate in a reduced state. molecular complementarity; vitamin C; seven-transmembrane-spanning membrane receptors  相似文献   

14.
Human lung epithelial (Calu-3) cells were used to investigate the effects of protease-activated receptor (PAR) stimulation on Cl secretion. Quantitative RT-PCR (QRT-PCR) showed that Calu-3 cells express PAR-1, -2, and -3 receptor mRNAs, with PAR-2 mRNA in greatest abundance. Addition of either thrombin or the PAR-2 agonist peptide SLIGRL to the basolateral solution of monolayers mounted in Ussing chambers produced a rapid increase in short-circuit current (Isc: thrombin, 21 ± 2 µA; SLIGRL, 83 ± 22 µA), which returned to baseline within 5 min after stimulation. Pretreatment of monolayers with the cell-permeant Ca2+-chelating agent BAPTA-AM (50 µM) abolished the increase in Isc produced by SLIGRL. When monolayers were treated with the cyclooxygenase inhibitor indomethacin (10 µM), nearly complete inhibition of both the thrombin- and SLIGRL-stimulated Isc was observed. In addition, basolateral treatment with the PGE2 receptor antagonist AH-6809 (25 µM) significantly inhibited the effects of SLIGRL on Isc. QRT-PCR revealed that Calu-3 cells express mRNAs for CFTR, the Ca2+-activated KCNN4 K+ channel, and the KCNQ1 K+ channel subunit, which, in association with KCNE3, is known to be regulated by cAMP. Stimulation with SLIGRL produced an increase in apical Cl conductance that was blocked in cells expressing short hairpin RNAs designed to target CFTR. These results support the conclusion that PAR stimulation of Cl secretion occurs by an indirect mechanism involving the synthesis and release of prostaglandins. In addition, PAR-stimulated Cl secretion requires activation of CFTR and at least two distinct K+ channels located in the basolateral membrane. cystic fibrosis transmembrane conductance regulator; KCNQ1; calcium-activated potassium channels; KCNN4; cAMP  相似文献   

15.
A study has been made of photosynthetic 14CO2 fixation by isolated‘mature’ internodes of Nitella translucens. Experimentalconditions were similar to those used in studies of the ionicrelations of these cells. Maximum rates of photosynthesis were33–40µµmoles CO2, fixed per cm2 of surfacearea per second (equivalent to 12–15 /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   

16.
The effects ofcyclopiazonic acid (CPA) were investigated on isolated skeletal musclefibers of frog semitendinosus muscle. CPA (0.5-10 µM) enhancedisometric twitch but produced little change in resting tension. Athigher concentrations (10-50 µM), CPA depressed twitch andinduced sustained contracture without affecting resting and actionpotentials. In Triton-skinned fibers, CPA had no significant effect onmyofibrillar Ca2+ sensitivity butdecreased maximal activated force at concentrations >5 µM. Inintact cells loaded with the Ca2+fluorescence indicator indo 1, CPA (2 µM) induced an increase inCa2+-transient amplitude (10 ± 2.5%), which was associated with an increase in time to peak and inthe time constant of decay. Consequently, peak force was increased by35 ± 4%, and both time to peak and the time constant of relaxationwere prolonged. It is concluded that CPA effects, at a concentration ofup to 2 µM, were associated with specific inhibition of sarcoplasmicreticulumCa2+-adenosinetriphosphatase inintact skeletal muscle and that inhibition of the pump directlyaffected the handling of intracellularCa2+ and force production.

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17.
The aim of the present study was to investigate the properties and role of capacitative Ca2+ entry (CCE) in interstitial cells (IC) isolated from the rabbit urethra. Ca2+ entry in IC was larger in cells with depleted intracellular Ca2+ stores compared with controls, consistent with influx via a CCE pathway. The nonselective Ca2+ entry blockers Gd3+ (10 µM), La3+ (10 µM), and Ni2+ (100 µM) reduced CCE by 67% (n = 14), 65% (n = 11), and 55% (n = 9), respectively. These agents did not inhibit Ca2+ entry when stores were not depleted. Conversely, CCE in IC was resistant to SKF-96365 (10 µM), wortmannin (10 µM), and nifedipine (1 µM). Spontaneous transient inward currents were recorded from IC voltage-clamped at –60 mV. These events were not significantly affected by Gd3+ (10 µM) or La3+ (10 µM) and were only slightly decreased in amplitude by 100 µM Ni2+. The results from this study demonstrate that freshly dispersed IC from the rabbit urethra possess a CCE pathway. However, influx via this pathway does not appear to contribute to spontaneous activity in these cells. smooth muscle; patch clamp; spontaneous transient inward currents  相似文献   

18.
Light-induced H+ transport of spinach chloroplasts was investigatedin the temperature range from 5° to 30°C with a glasselectrode. The rate of H+ transport was reduced by lowering the temperature.Addition of 1 µM phenazine methosulfate (PMS) considerablystimulated the H+ uptake in chloroplasts. PMS was also effectivein stimulating the H+ efflux when the illumination was turnedoff. The latter effect became more marked at lower temperatures.These results indicate that electron transfer reactions in thechloroplast not only drive the forward process of H+ gradientformation, but also participate in the backward H+ efflux. The Arrhenius plot applied to the first-order rate constantof the H+ efflux showed a discontinuity at about 20°C. Nohysteresis was detected with the temperature dependence andits discontinuity in the H+ transport. On the other hand, theaddition of PMS abolished the discontinuity and a linear relationshipwas observed in the Arrhenius plot. Probably, temperature-dependentphysical changes in the microenvironment of the chloroplastlamellae are responsible for determining the characteristicsof the H+transport. (Received September 11, 1975; )  相似文献   

19.
Seedlings of Italian ryegrass (Lolium multiflorum Lam. cv. RVP)and clonal stolon cuttings of white clover (Trifolium repensL. cv. Blanca) were grown for 19 d in flowing solution culture,with N supplied as either 250 mmol m–3 NO3 or NH3+.Rates of net uptake, influx and translocation of NO3and NH4+ were then determined using 15N and 13N labelling techniques:between 3–5 h into the photoperiod following 8 h darknessfor white clover (CL), and for ryegrass plants that were eitherentire (IL) or with shoots excised 90 min prior to 13N influx(IC); and 75 min into the photoperiod following 37–39h darkness for ryegrass (ID). Rates of net uptake, influx andefflux of NH4+ exceeded those of NO3 in IL and IC ryegrassplants: the opposite occurred in white clover (CL). The decreasein net uptake following defoliation of ryegrass was greaterfor NH4+ (62%) than NO3 (40%). For NH4+ this was associatedwith a large decrease in influx from 110 to 6.0µmol h–1g–1 root fr. wt; but for NO3, influx only decreasedfrom 42 to 37 µmol h–1 g–1. Prolonged exposureto darkness (ID plants) also lowered net uptake of NO3and NH4+ by, respectively, 86% and 95% of IL levels. For NH4+this was characterized by a large decrease in influx and a smalldecrease in efflux; whilst for NO3 the effect of a largedecrease in influx was reinforced by a smaller increase in efflux. The data were used to estimate the translocatory fluxes of NO3(03–20µmol h–1 g–1) and NH4+ (003–0.4µmolh–1 g–1), assimilation in the roots of NO3(02–26µmol h–1 g–1) and NH+4 (05–89 µmolh–1 g–1), and the concentrations of NO3 (9–15mol m–3) in the cytoplasmic compartment of the roots.The relevance of variable influx and efflux to models for theregulation of N uptake is discussed. Key words: Lolium multiflorum, Trifolium repens, influx, efflux, nitrate, ammonium, 13N  相似文献   

20.
This study reports the identification and characterization ofallyl diphosphatases (EC 3.1.7.1) in plants by using rice seedlings.Two distinct Mg2+-independent allyl diphosphatases, which convertfarnesyl diphosphate (FDP) and geranylgeranyl diphosphate (GGDP)into farnesol and geranylgeraniol, respectively, were inducedin rice seedlings irradiated with UV-C. Farnesyl diphosphatase(FDPase) and geranylgeranyl diphosphatase (GGDPase) are locatedin the microsomal fraction. The relative specific activity ofFDPase was much higher than the specific activity of GGDPase.FDPase activity was inhibited by GGDP (50% inhibition at 5 µM)and geranyl diphosphate (50% inhibition at 100 µM).In contrast, GGDPase activity was inhibited 50% by 50 µMisopentenyl diphosphate or 100 µM FDP. The optimalpH for FDPase was 6.3 and for GGDPase was 7.9. 1 Corresponding author: E-mail, kback@chonnam.chonnam.ac.kr;Fax, +82-62-530-2169.  相似文献   

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