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1.
Gametophytes of the fern Asplenium trichomanes exhibit guttationwhen illuminated. Membrane potential changes evoked by lightwere measured in the presence of ion channel and proton pumpinhibitors to elucidate the nature of the response and a possiblelink to guttation. Light-induced depolarization was suppressedby the anion channel inhibitors: anthracene-9-carboxylic acidand niflumic acid. Potassium channel blockers: TEA and Ba2+caused an increase of the amplitude of light-induced membranepotential changes. Calcium channel inhibitors, La3+ Gd3+ diltiazem,nifedipine and verapamil had no significant effect on the membranepotential changes. Similarly, proton pump inhibitors, diethylstilbestroland vanadate, had only minor effects on the response. A possiblerole of Cl and K+ fluxes in light-induced guttation isdiscussed. (Received July 8, 1999; Accepted October 13, 1999)  相似文献   

2.
The role of nitric oxide (NO) in the occurrence of intracellular Ca2+ concentration ([Ca2+]i) oscillations in pituitary GH3 cells was evaluated by studying the effect of increasing or decreasing endogenous NO synthesis with L-arginine and nitro-L-arginine methyl ester (L-NAME), respectively. When NO synthesis was blocked with L-NAME (1 mM) [Ca2+]i, oscillations disappeared in 68% of spontaneously active cells, whereas 41% of the quiescent cells showed [Ca2+]i oscillations in response to the NO synthase (NOS) substrate L-arginine (10 mM). This effect was reproduced by the NO donors NOC-18 and S-nitroso-N-acetylpenicillamine (SNAP). NOC-18 was ineffective in the presence of the L-type voltage-dependent Ca2+ channels (VDCC) blocker nimodipine (1 µM) or in Ca2+-free medium. Conversely, its effect was preserved when Ca2+ release from intracellular Ca2+ stores was inhibited either with the ryanodine-receptor blocker ryanodine (500 µM) or with the inositol 1,4,5-trisphosphate receptor blocker xestospongin C (3 µM). These results suggest that NO induces the appearance of [Ca2+]i oscillations by determining Ca2+ influx. Patch-clamp experiments excluded that NO acted directly on VDCC but suggested that NO determined membrane depolarization because of the inhibition of voltage-gated K+ channels. NOC-18 and SNAP caused a decrease in the amplitude of slow-inactivating (IDR) and ether-à-go-go-related gene (ERG) hyperpolarization-evoked, deactivating K+ currents. Similar results were obtained when GH3 cells were treated with L-arginine. The present study suggests that in GH3 cells, endogenous NO plays a permissive role for the occurrence of spontaneous [Ca2+]i oscillations through an inhibitory effect on IDR and on IERG. voltage-gated potassium channels; ether-à-go-go-related gene potassium channels; slow-inactivating outward currents; fast-inactivating outward currents  相似文献   

3.
The control of the activity of the matrix-located malic enzyme(EC 1.1.1.39 [EC] ) by Mn2+ was investigated in Percoll-purified mitochondriafrom potato (Solarium tuberosum) tuber. Malic enzyme activitywas tightly controlled by the amount of Mn2+ available in thematrix space and could be stimulated by the addition of exogenousMn2+. A net uptake of Mn2+ into the matrix space of energizedmitochondria was measured. The uptake of Mn2+ was mediated bythe active cation pump present in the mitochondria. The activityof this cation pump was shown to be dependent on the membranepotential sustained by the activity of the respiratory chain.The uptake of Mn2+ was totally abolished in the presence ofan uncoupler and strongly depressed in the presence of rutheniumred, a specific inhibitor of the Ca2+-pump which is presentin animal mitochondria. Thus, the effect of Mn2+ on matrix-locatedMn2+-dependent malic enzyme was strongly influenced by the presenceof an uncoupler or of ruthenium red. In addition, this effectwas reduced in the presence of Ca2+. The possible physiologicalsignificance of the presence of this cation pump is discussedin relation to the presence of a matrix-located, NAD+-dependentmalic enzyme in plant mitochondria. (Received November 21, 1988; Accepted March 6, 1989)  相似文献   

4.
Spiral waves of intracellularCa2+ have often been observed inXenopus oocytes. Such waves can beaccounted for by most realistic models forCa2+ oscillations taking diffusionof cytosolic Ca2+ into account,but their initiation requires rather demanding and unphysiologicalinitial conditions. Here, it is shown by means of numerical simulationsthat these spiral Ca2+ wavesnaturally arise if the cytoplasm is assumed to be heterogeneous both atthe level of the synthesis and metabolism ofD-myo-inositol 1,4,5-trisphosphate[Ins(1,4,5)P3]and at the level of the distribution of theIns(1,4,5)P3receptors. In such conditions, a spiral can be initiated in thesimulations after an increase inIns(1,4,5)P3 concentration, with the direction of rotation being determined by theposition of the region of high receptor density with respect to thelocus ofIns(1,4,5)P3production.

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5.
Effect of Sudden Salt Stress on Ion Fluxes in Intact Wheat Suspension Cells   总被引:4,自引:0,他引:4  
Although salinity is one of the major problems limiting agriculturalproduction around the world, the underlying mechanisms of highNaCl perception and tolerance are still poorly understood. Theeffects of different bathing solutions and fusicoccin (FC),a known activator of plasma membrane ATPase, on plasma membranepotential (Em) and net fluxes of Na+, K+and H+were studied inwheat suspension cells (Triticum aestivum) in response to differentNaCl treatments. Emof cells in Murashige and Skoog (MS) mediumwas less negative than in cells exposed to a medium containing10 mM KCl + 0.1 m M CaCl2(KSM) and to a basic salt medium (BSM),containing 1 m M KCl and 0.1 m M CaCl2. Multiphasic Na+accumulationin cells was observed, peaking at 13 min after addition of 120m M NaCl to MS medium. This time scale was in good agreementwith net Na+flux changes measured non-invasively by moving ion-selectivemicroelectrodes (the MIFE system). When 120 m M NaCl was addedto all media studied, a quick rise of Na+influx was reversedwithin the first 20 min. In both 120 and 20 m M NaCl treatmentsin MS medium, net Na+efflux was observed, indicating that activeNa+transporters function in the plant cell response to saltstress. Lower external K+concentrations (KSM and BSM) and FCpre-treatment caused shifts in Na+fluxes towards net influxat 120 m M NaCl stress. Copyright 2000 Annals of Botany Company Sodium, potassium, proton, membrane potential, fusicoccin, salt stress, wheat, Triticum aestivum  相似文献   

6.
Microgravity has been shown to alterprotein kinase C (PKC) activity; therefore, we investigated whethermicrogravity influences mechanically stimulated Ca2+signaling and ATP-induced Ca2+ oscillations, both of whichare modulated by PKC. Rabbit tracheal epithelial outgrowth cultures orsuspended epithelial sheets were rotated in bioreactors to simulatemicrogravity. Mechanical stimulation of a single cell increased thecytosolic Ca2+ concentration in 35-55 cells of bothoutgrowth cultures and epithelial sheets kept at unit gravity (G) or insimulated microgravity (sµG). In outgrowth cultures,12-O-tetradecanoylphorbol-13-acetate (TPA; 80 nM), a PKCactivator, restricted Ca2+ "waves" to about 10 cells inunit G and to significantly fewer cells in sµG. TPA only slightlyreduced the spread of Ca2+ waves in epithelial sheets keptin sµG but did not inhibit Ca2+ waves of sheets kept inunit G. In both cell preparations from both conditions, TPA inhibitedATP-induced Ca2+ oscillations; however, the effect was morepronounced in cells kept in sµG. These results suggest that PKCactivation is more robust in cells subjected to sµG.

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7.
We investigatedthe relationship between voltage-operatedCa2+ channel current and thecorresponding intracellular Ca2+concentration([Ca2+]i)change (Ca2+ transient) in guineapig gastric myocytes. Fluorescence microspectroscopy was combined withconventional whole cell patch-clamp technique, and fura 2 (80 µM) wasadded to CsCl-rich pipette solution. Step depolarization to 0 mVinduced inward Ca2+ current(ICa) andconcomitantly raised[Ca2+]i.Both responses were suppressed by nicardipine, an L-typeCa2+ channel blocker, and thevoltage dependence of Ca2+transient was similar to the current-voltage relation ofICa. When pulseduration was increased by up to 900 ms, peakCa2+ transient increased andreached a steady state when stimulation was for longer. The calculatedfast Ca2+ buffering capacity(B value), determined as the ratio ofthe time integral ofICa divided bythe amplitude of Ca2+ transient,was not significantly increased after depletion of Ca2+ stores by the cyclicapplication of caffeine (10 mM) in the presence of ryanodine (4 µM).The addition of cyclopiazonic acid (CPA, 10 µM), a sarco(endo)plasmicreticulum Ca2+-ATPase inhibitor,decreased B value by ~20% in areversible manner. When KCl pipette solution was used,Ca2+-activatedK+ current[IK(Ca)]was also recorded during step depolarization. CPA sensitivelysuppressed the initial peak and oscillations of IK(Ca) withirregular effects on Ca2+transients. The above results suggest that, in guinea pig gastric myocyte, Ca2+ transient is tightlycoupled to ICaduring depolarization, and global[Ca2+]iis not significantly affected byCa2+-inducedCa2+ release from sarcoplasmicreticulum during depolarization.

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8.
Movement of Ions and Electrogenesis in Microorganisms   总被引:5,自引:0,他引:5  
The relationship between movement of ions and the electricalproperties of microorganisms (algae, fungi, and bacteria) arereviewed, with particular emphasis on the giant alga, Nitella,and the fungus, Neurospora. The hypothesis is presented thatthere are two basically different components to the membranepotential of both organisms: (1) one arising from the diffusionof sodium, potassium, and hydrogen ions down their chemicalgradients, and (2) one associated with the utilization of energyand the active efflux of hydrogen ions, and attributed to an"electrogenic H+ pump." Numerous discrepancies between the measuredelectrical properties of the algae or fungi and the predictionsof ordinary ion-diffusion theory can be accounted for by suchan H+ pump, and its existence is further supported by a fewindirect experiments on the bacteria.  相似文献   

9.
LocalCa2+ transients("Ca2+ sparks") caused bythe opening of one or the coordinated opening of a number of tightlyclustered ryanodine-sensitiveCa2+-release (RyR) channels in thesarcoplasmic reticulum (SR) activate nearbyCa2+-dependentK+(KCa) channels to cause anoutward current [referred to as a "spontaneous transientoutward current" (STOC)]. TheseKCa currents cause membranepotential hyperpolarization of arterial myocytes, which would lead tovasodilation through decreasingCa2+ entry throughvoltage-dependent Ca2+ channels.Therefore, modulation of Ca2+spark frequency should be a means to regulation ofKCa channel currents and hencemembrane potential. We examined the frequency modulation ofCa2+ sparks and STOCs byactivation of protein kinase C (PKC). The PKC activators, phorbol12-myristate 13-acetate (PMA; 10 nM) and 1,2-dioctanoyl-sn-glycerol (1 µM),decreased Ca2+ spark frequency by72% and 60%, respectively, and PMA reduced STOC frequency by 83%.PMA also decreased STOC amplitude by 22%, which could be explained byan observed reduction (29%) inKCa channel open probability inthe absence of Ca2+ sparks. Thereduction in STOC frequency occurred in the presence of an inorganicblocker (Cd2+) ofvoltage-dependent Ca2+ channels.The reduction in Ca2+ sparkfrequency did not result from SRCa2+ depletion, sincecaffeine-induced Ca2+ transientsdid not decrease in the presence of PMA. These results suggest thatactivators of PKC can modulate the frequency ofCa2+ sparks, through an effect onthe RyR channel, which would decrease STOC frequency (i.e.,KCa channel activity).

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10.
Agonist stimulation of human pulmonary artery smooth muscle cells (PASMC) and endothelial cells (PAEC) with histamine showed similar spatiotemporal patterns of Ca2+ release. Both sustained elevation and oscillatory patterns of changes in cytosolic Ca2+ concentration ([Ca2+]cyt) were observed in the absence of extracellular Ca2+. Capacitative Ca2+ entry (CCE) was induced in PASMC and PAEC by passive depletion of intracellular Ca2+ stores with 10 µM cyclopiazonic acid (CPA; 15–30 min). The pyrazole derivative BTP2 inhibited CPA-activated Ca2+ influx, suggesting that depletion of CPA-sensitive internal stores is sufficient to induce CCE in both PASMC and PAEC. The recourse of histamine-mediated Ca2+ release was examined after exposure of cells to CPA, thapsigargin, caffeine, ryanodine, FCCP, or bafilomycin. In PASMC bathed in Ca2+-free solution, treatment with CPA almost abolished histamine-induced rises in [Ca2+]cyt. In PAEC bathed in Ca2+-free solution, however, treatment with CPA eliminated histamine-induced sustained and oscillatory rises in [Ca2+]cyt but did not affect initial transient increase in [Ca2+]cyt. Furthermore, treatment of PAEC with a combination of CPA (or thapsigargin) and caffeine (and ryanodine), FCCP, or bafilomycin did not abolish histamine-induced transient [Ca2+]cyt increases. These observations indicate that 1) depletion of CPA-sensitive stores is sufficient to cause CCE in both PASMC and PAEC; 2) induction of CCE in PAEC does not require depletion of all internal Ca2+ stores; 3) the histamine-releasable internal stores in PASMC are mainly CPA-sensitive stores; 4) PAEC, in addition to a CPA-sensitive functional pool, contain other stores insensitive to CPA, thapsigargin, caffeine, ryanodine, FCCP, and bafilomycin; and 5) although the CPA-insensitive stores in PAEC may not contribute to CCE, they contribute to histamine-mediated Ca2+ release. intracellular calcium stores; oscillations; pulmonary hypertension  相似文献   

11.
Enterochromaffin-like (ECL) cells are histamine-containingendocrine cells in the gastric mucosa that maintain a negative membranepotential of about 50 mV, largely due to voltage-gated K+ currents [D. F. Loo, G. Sachs, and C. Prinz. Am. J. Physiol. 270 (Gastrointest Liver Physiol. 33):G739-G745, 1996]. The current study investigated thepresence of voltage-gated Ca2+channels in single ECL cells. ECL cells were isolated from rat fundicmucosa by elutriation, density gradient centrifugation, and primaryculture to a purity >90%. Voltage-gatedCa2+ currents were measured insingle ECL cells using the whole cell configuration of the patch-clamptechnique. Depolarization-activated currents were recorded in thepresence of Na+ orK+ blocking solutions and additionof 20 mM extracellular Ca2+. ECLcells showed inward currents in response to voltage steps that wereactivated at a test potential of around 20 mV with maximalinward currents observed at +20 mV and 20 mM extracellular Ca2+. The inactivation rate of thecurrent decreased with increasingly negative holding potentials and wastotally abolished at a holding potential of 30 mV. Addition ofextracellular 20 mM Ba2+ insteadof 20 mM Ca2+ increased thedepolarization-induced current and decreased the inactivation rate. Theinward current was fully inhibited by the specific L-typeCa2+ channel inhibitor verapamil(0.2 mM) and was augmented by the L-typeCa2+ channel activator BAY K 8644 (0.07 mM). We conclude that depolarization activateshigh-voltage-activated Ca2+channels in ECL cells. Activation characteristics,Ba2+ effects, and pharmacologicalresults imply the presence of L-type Ca2+ channels, whereasinactivation kinetics suggest the presence of additional N-typechannels in rat gastric ECL cells.

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12.
The relationship between dissipation of the flash-induced membranepotential across the thylakoid membrane and the high energystate was studied in Zea mays leaves. The dark decay of theflash-induced 515-nm absorbance change was accelerated by shortpreillumination of the leaf. No acceleration of the decay bypreillumination was observed when leaves were incubated in argonor CO2 gas or treated with DCMU. These effects of preilluminationand incubation were reversible. The delayed fluorescence from chlorophyll a was reversibly decreasedby incubating leaves in argon or CO2 gas, though the modes ofdepression were somewhat different from each other. In leavesincubated in argon or CO2 gas, the phase of slow decrease ofthe intensity of prompt fluorescence during illumination reversiblydisappeared. The results suggested that the dissipation of membrane potentialgenerated by a flash was accelerated after the energizationof chloroplasts in leaves, probably by increased H permeabilityof the thylakoid membrane. O2 was important in maintaining (indarkness) and forming (under illumination) the high energy statein chloroplasts in intact leaves. (Received October 1, 1980; Accepted December 15, 1980)  相似文献   

13.
We employed a glycogen-depleting session of exercise followed by a low-carbohydrate (CHO) diet to investigate modifications that occur in muscle sarcoplasmic reticulum (SR) Ca2+-cycling properties compared with low-CHO diet alone. SR properties were assessed in nine untrained males [peak aerobic power (O2 peak) = 43.6 ± 2.6 (SE) ml·kg–1·min–1] during prolonged cycle exercise to fatigue performed at 58% O2 peak after 4 days of low-CHO diet (Lo CHO) and after glycogen-depleting exercise plus 4 days of low-CHO (Ex+Lo CHO). Compared with Lo CHO, Ex+Lo CHO resulted in 12% lower (P < 0.05) resting maximal Ca2+-ATPase activity (Vmax = 174 ± 12 vs. 153 ± 10 µmol·g protein–1·min–1) and smaller reduction in Vmax induced during exercise. A similar effect was observed for Ca2+ uptake. The Hill coefficient, defined as slope of the relationship between cytosolic free Ca2+ concentration and Ca2+-ATPase activity, was higher (P < 0.05) at rest (2.07 ± 0.15 vs. 1.90 ± 0.10) with Ex+Lo CHO, an effect that persisted throughout the exercise. The coupling ratio, defined as the ratio of Ca2+ uptake to Vmax, was 23–30% elevated (P < 0.05) at rest and during the first 60 min of exercise with Ex+Lo CHO. The 27 and 34% reductions (P < 0.05) in phase 1 and phase 2 Ca2+ release, respectively, observed during exercise with Lo CHO were not altered by Ex+Lo CHO. These results indicate that when prolonged exercise precedes a short-term Lo CHO diet, Ca2+ sequestration properties and efficiency are improved compared with those during Lo CHO alone. calcium cycling; vastus lateralis; contractile activity; glycogen; phosphorylation potential  相似文献   

14.
The intent of this work was to evaluate the role of cAMP inregulation of ciliary activity in frog mucociliary epithelium and toexamine the possibility of cross talk between the cAMP- andCa2+-dependent pathways in thatregulation. Forskolin and dibutyryl cAMP induced strong transientintracellular Ca2+ concentration([Ca2+]i)elevation and strong ciliary beat frequency enhancement with prolongedstabilization at an elevated plateau. The response was not affected byreduction of extracellular Ca2+concentration. The elevation in[Ca2+]iwas canceled by pretreatment with1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid-AM, thapsigargin, and a phospholipase C inhibitor, U-73122. Underthose experimental conditions, forskolin raised the beat frequency to amoderately elevated plateau, whereas the initial strong rise infrequency was completely abolished. All effects were canceled by H-89,a selective protein kinase A (PKA) inhibitor. The results suggest adual role for PKA in ciliary regulation. PKA releasesCa2+ from intracellular stores,strongly activating ciliary beating, and, concurrently, producesmoderate prolonged enhancement of the beat frequency by aCa2+-independent mechanism.

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15.
In this report we describe a mathematical model for the regulation of cAMP dynamics in pancreatic β-cells. Incretin hormones such as glucagon-like peptide 1 (GLP-1) increase cAMP and augment insulin secretion in pancreatic β-cells. Imaging experiments performed in MIN6 insulinoma cells expressing a genetically encoded cAMP biosensor and loaded with fura-2, a calcium indicator, showed that cAMP oscillations are differentially regulated by periodic changes in membrane potential and GLP-1. We modeled the interplay of intracellular calcium (Ca2+) and its interaction with calmodulin, G protein-coupled receptor activation, adenylyl cyclases (AC), and phosphodiesterases (PDE). Simulations with the model demonstrate that cAMP oscillations are coupled to cytoplasmic Ca2+ oscillations in the β-cell. Slow Ca2+ oscillations (<1 min–1) produce low-frequency cAMP oscillations, and faster Ca2+ oscillations (>3–4 min–1) entrain high-frequency, low-amplitude cAMP oscillations. The model predicts that GLP-1 receptor agonists induce cAMP oscillations in phase with cytoplasmic Ca2+ oscillations. In contrast, observed antiphasic Ca2+ and cAMP oscillations can be simulated following combined glucose and tetraethylammonium-induced changes in membrane potential. The model provides additional evidence for a pivotal role for Ca2+-dependent AC and PDE activation in coupling of Ca2+ and cAMP signals. Our results reveal important differences in the effects of glucose/TEA and GLP-1 on cAMP dynamics in MIN6 β-cells. adenylyl cyclase; calcium ion; glucagon-like peptide 1; modeling; oscillations  相似文献   

16.
Inisolated rat pancreatic -cells, the nitric oxide (NO) donor NOC-7 at1 µM reduced the amplitude of the oscillations of cytosolicCa2+ concentration ([Ca2+]c)induced by 11.1 mM glucose, and at 10 µM terminated them. In thepresence of NG-nitro-L-arginine(L-NNA), however, NOC-7 at 0.5 and 1 µM increased theamplitude of the [Ca2+]c oscillations,although the NO donor at 10 µM still suppressed them. Aqueous NOsolution also had a dual effect on the[Ca2+]c oscillations. The soluble guanylatecyclase inhibitor LY-83583 and the cGMP-dependent protein kinaseinhibitor KT5823 inhibited the stimulatory effect of NO, and8-bromo-cGMP increased the amplitude of the[Ca2+]c oscillations. Patch-clamp analyses inthe perforated configuration showed that 8-bromo-cGMP inhibited wholecell ATP-sensitive K+ currents in the isolated ratpancreatic -cells, suggesting that the inhibition by cGMP ofATP-sensitive K+ channels is, at least in part, responsiblefor the stimulatory effect of NO on the[Ca2+]c oscillations. In the presence ofL-NNA, the glucose-induced insulin secretion from isolatedislets was facilitated by 0.5 µM NOC-7, whereas it was suppressed by10 µM NOC-7. These results suggest that NO facilitatesglucose-induced [Ca2+]c oscillations of-cells and insulin secretion at low concentrations, which effectsare mediated by cGMP, whereas NO inhibits them in a cGMP-independentmanner at high concentrations.

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17.
The mechanism involved inN-methyl-D-glucamine(NMDA)-induced Ca2+-dependentintracellular acidosis is not clear. In this study, we investigated indetail several possible mechanisms using cultured rat cerebellargranule cells and microfluorometry [fura 2-AM or 2',7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein-AM].When 100 µM NMDA or 40 mM KCl was added, a marked increase in theintracellular Ca2+ concentration([Ca2+]i)and a decrease in the intracellular pH were seen. Acidosis wascompletely prevented by the use ofCa2+-free medium or1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid-AM, suggesting that it resulted from an influx of extracellular Ca2+. The following fourmechanisms that could conceivably have been involved were excluded:1)Ca2+ displacement of intracellularH+ from common binding sites;2) activation of an acid loader or inhibition of acid extruders; 3)overproduction of CO2 or lactate; and 4) collapse of the mitochondrialmembrane potential due to Ca2+uptake, resulting in inhibition of cytosolicH+ uptake. However,NMDA/KCl-induced acidosis was largely prevented by glycolyticinhibitors (iodoacetate or deoxyglucose in glucose-free medium) or byinhibitors of the Ca2+-ATPase(i.e.,Ca2+/H+exchanger), including La3+,orthovanadate, eosin B, or an extracellular pH of 8.5. Our results therefore suggest that Ca2+-ATPaseis involved in NMDA-induced intracellular acidosis in granule cells. Wealso provide new evidence that NMDA-evoked intracellular acidosisprobably serves as a negative feedback signal, probably with theacidification itself inhibiting the NMDA-induced[Ca2+]i increase.

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18.
Calcium ion is a key messenger in turgor regulation of internodalcells of Lamprothamnium succinctum in response to hypoosmotictreatment. An increase in the concentration of cytosolic freecalcium ion ([Ca2+]c) is prerequisite for the turgor regulation[Okazaki and Tazawa (1990) J. Membr. Biol. 114: 189], We examinedwhether or not a calcium-dependent protein kinase (CDPK) isinvolved in the Ca2+-mediated turgor regulation of Lamprothamniumcells. A 53-kDa CDPK which phosphorylated preferentially histoneH1 but poorly myelin basic protein or casein, was detected inthe cell extract of Lamprothamnium by an in-gel protein kinaseassay. This protein kinase was detected by Western blottingand was immunoprecipitated using an anti-Dunaliella tertiolectaCDPK antibody which can neutralize the Dunaliella CDPK activity[Yuasa et al. (1995) Plant Cell Physiol. 36: 699]. The 53-kDaCDPK was partially purified from Lamprothamnium and its activitywas shown to be inhibited by the antibody and K-252a, a proteinkinase inhibitor. Microinjection of the antibody into the cytosblof Lamprothamnium cells inhibited the decrease in turgor pressurein response to hypoosmotic treatment. However, a transient increasein [Ca2+]c, which was suggested by a transient reduction ofthe velocity of cytoplasmic streaming, was induced in antibody-injectedcells after hypoosmotic treatment. Turgor regulation upon hypoosmotictreatment was inhibited when the cells were treated with K-252a.These results imply that CDPK of Lamprothamnium functions ata down-stream position of Ca2+-mobilization in processing turgorregulation in response to hypoosmotic treatment. 2 These authors contributed equally to the work.  相似文献   

19.
Using glass capillary microelectrodes for the measurement ofpotential differences (PD) and antimony microelectrodes forthe measurement of pH, we investigated the light-induced changesof PD between the central vacuole and the external medium, ofpH in the vacuole (pHv), as well as of pH in the external medium(pHo) of the green marine alga Valonia ventricosa. PD in thedark was about +30 to +40 mV (vacuole positive), pHv 6.3, andthe resistance of the protoplast (cell wall-plasmalemma-tonoplast)17.8 kOhm cm2. Illumination caused an increase of the positivePD (after a few oscillations) up to +80 to +100 mV, acidificationof the vacuolar sap, alkalinization of the external medium,and a decrease in the resistance of the protoplast to 7.6 kOhmcm2. The kinetics of the changes of PD, pHv, and pHo were similarto each other. It is concluded that a light-stimulated activeH+ flow occurs from the external medium into the central vacuoleof Valonia ventricosa as a result of the onset of photosyntheticactivity.  相似文献   

20.
Pulmonary vasoconstriction and vascularmedial hypertrophy greatly contribute to the elevated pulmonaryvascular resistance in patients with pulmonary hypertension. A rise incytosolic free Ca2+ ([Ca2+]cyt)in pulmonary artery smooth muscle cells (PASMC) triggers vasoconstriction and stimulates cell growth. Membrane potential (Em) regulates[Ca2+]cyt by governing Ca2+influx through voltage-dependent Ca2+ channels. Thusintracellular Ca2+ may serve as a shared signaltransduction element that leads to pulmonary vasoconstriction andvascular remodeling. In PASMC, activity of voltage-gated K+(Kv) channels regulates resting Em. In thisstudy, we investigated whether changes of Kv currents[IK(V)], Em, and[Ca2+]cyt affect cell growth by comparingthese parameters in proliferating and growth-arrested PASMC. Serumdeprivation induced growth arrest of PASMC, whereas chelation ofextracellular Ca2+ abolished PASMC growth. Resting[Ca2+]cyt was significantly higher, andresting Em was more depolarized, inproliferating PASMC than in growth-arrested cells. Consistently, wholecell IK(V) was significantly attenuated in PASMCduring proliferation. Furthermore, Emdepolarization significantly increased resting[Ca2+]cyt and augmented agonist-mediatedrises in [Ca2+]cyt in the absence ofextracellular Ca2+. These results demonstrate that reducedIK(V), depolarized Em, and elevated [Ca2+]cyt may play a criticalrole in stimulating PASMC proliferation. Pulmonary vascular medialhypertrophy in patients with pulmonary hypertension may be partlycaused by a membrane depolarization-mediated increase in[Ca2+]cyt in PASMC.

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