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1.
OWEN JOHN H.; HETHERINGTON ALISTAIR M.; WELLBURN ALAN R. 《Journal of experimental botany》1987,38(8):1356-1361
Owen, J. H., Hetherington, A. M. and Wellburn, A. R. 1987. Calcium,calmodulin and the control of respiration in protoplasts isolatedfrom meristematic tissues by abscisic acid.J. exp. Bot.38: 13561361. A study was made of the possible involvement of calcium channelsand calmodulin during the calcium-dependent inhibition of mitochondrialrespiration by abscisic acid (ABA) in meristematic protoplastsobtained from light-grown barley (Hordeum vulgare L. cv. Patty)seedlings. The calcium channel blockers lanthanum, verapamiland nifedipine were all found to reduce the Ca2+-dependent inhibitionof protoplast respiration by ABA. The ionophore A23187
[GenBank] itselfcaused an inhibition of protoplast respiration, possibly becauseit mimicked the action of ABA by increasing plasmalemma permeabilityto extracellular calcium. By contrast, calmodulin antagoniststrifluoperazine and compound 48/80 both caused a partial decreasein the Ca2+-dependent inhibition of protoplast respiration byABA. In contrast to the action of ABA, gibberellic acid markedlyincreased the rates of protoplast respiration but this did notappear to require the presence of extracellular calcium ions.These results support the hypothesis that ABA increases plasmalemmapermeability to extracellular calcium which might then directlyor indirectly act as a second messenger, possibly in conjunctionwith calmodulin, to regulate mitochondrial dark respirationwhich is an important part of early meristematic cell development. Key words: Abscisic acid, calcium, calmodulin, meristematic respiration 相似文献
2.
An interaction between aluminium (Al) and calcium (Ca) may bea cause of Al toxicity in plants. The pollen tube is a suitablesystem to test the interaction between Al and Ca since Ca ionsplay a pivotal role in pollen germination and tube growth. Weinvestigated how Al and other known blockers of Ca2+-permeablechannels (trivalent cations, ruthenium red, verapamil and nifedipine)influence pollen of an Australian native species Geraldton waxflower(Chamelaucium uncinatum). Pollen germination was inhibited bymicromolar concentrations of trivalent cations (La3+>Al3+>Gd3+)and ruthenium red, but it was relatively insensitive to a micromolarconcentration of verapamil. Exposure of the growing pollen tubesto micromolar concentrations of Al3+and La3+, and a millimolarconcentration of Ca2+chelator ethyleneglycol-bis(ß-aminoethylether)-N,N'-tetraacetic acid (EGTA) led to rapid tip bursting.In contrast, exposure to Gd3+, nifedipine, ruthenium red, verapamiland the organic trivalent cation tris (ethylenediamine)cobalt(TEC3+) caused only inhibition of pollen tube growth. The Al3+-relatedpollen tube bursting was reduced significantly by increasingeither solution pH from 4.5 to 6 or activity of Ca2+from 0.25to 5 m M. In contrast, La3+-related pollen tube bursting wasinsensitive to changes in Ca2+activity. The results are discussedin terms of Al interactions with cell wall Ca2+and the plasmamembrane Ca2+-permeable channels. Copyright 1999 Annals of BotanyCompany Aluminium toxicity, Ca2+-channel blockers, cell wall, Chamelaucium uncinatum, pollen germination, pollen tube growth. 相似文献
3.
4.
Ca(2+) regulates fluid shear-induced cytoskeletal reorganization and gene expression in osteoblasts 总被引:13,自引:0,他引:13
Chen NX Ryder KD Pavalko FM Turner CH Burr DB Qiu J Duncan RL 《American journal of physiology. Cell physiology》2000,278(5):C989-C997
Osteoblasts subjected to fluid shearincrease the expression of the early response gene, c-fos, andthe inducible isoform of cyclooxygenase, COX-2, two proteins linked tothe anabolic response of bone to mechanical stimulation, in vivo. Theseincreases in gene expression are dependent on shear-induced actinstress fiber formation. Here, we demonstrate that MC3T3-E1osteoblast-like cells respond to shear with a rapid increase inintracellular Ca2+ concentration([Ca2+]i) that wepostulate is important to subsequent cellular responses to shear. Totest this hypothesis, MC3T3-E1 cells were grown on glass slides coatedwith fibronectin and subjected to laminar fluid flow (12 dyn/cm2). Before application of shear, cells were treatedwith two Ca2+ channel inhibitors or various blockers ofintracellular Ca2+ release for 0.5-1 h. Althoughgadolinium, a mechanosensitive channel blocker, significantly reducedthe [Ca2+]i response, neithergadolinium nor nifedipine, an L-type channel Ca2+ channelblocker, were able to block shear-induced stress fiber formation andincrease in c-fos and COX-2 in MC3T3-E1 cells. However, 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraaceticacid-AM, an intracellular Ca2+ chelator, or thapsigargin,which empties intracellular Ca2+ stores, completelyinhibited stress fiber formation and c-fos/COX-2 production in shearedosteoblasts. Neomycin or U-73122 inhibition of phospholipase C, whichmediates D-myo-inositol 1,4,5-trisphosphate (IP3)-induced intracellular Ca2+ release, alsocompletely suppressed actin reorganization and c-fos/COX-2 production.Pretreatment of MC3T3-E1 cells with U-73343, the inactive isoform ofU-73122, did not inhibit these shear-induced responses. These resultssuggest that IP3-mediated intracellular Ca2+release is required for modulating flow-induced responses in MC3T3-E1 cells. 相似文献
5.
Effects of Calcium and Abscisic Acid on Volume Changes of Guard Cell Protoplasts of Commelina 总被引:1,自引:0,他引:1
Calcium ions contracted guard cell protoplasts (GCP) of Commelinacommunis L., being particularly effective within the concentrationrange of 0 to 0.2 mol m3. Abscisic acid (ABA) in thepresence of EGTA, which chelates free Ca2+ in the medium, contractedGCP to a similar extent to Ca2+ alone or Ca2+ and ABA together.Similarly, ABA in the absence of free Ca2+ (i.e. an ABA/EGTAtreatment) inhibited K+-induced swelling of contracted GCP,as did Ca2+ alone or ABA and Ca2+ together. Lanthanum, a Ca2+channel blocker, prevented the contraction of GCP by Ca2+ buthad no effect if ABA was also present with Ca2+. The inhibitionof swelling of GCP by Ca2+ was also prevented by the presenceof lanthanum or verapamil (another Ca2+ channel blocker). These results indicate that Ca2+ and ABA can act independentlyof each other in contracting swollen GCP and in preventing K+-inducedswelling of contracted GCP of C. communis. If swelling and contractionof GCP are equivalent to stomatal opening and closure, respectively,the results do not support the hypothesis that ABA opens Ca2+channels in the plasma membrane of guard cells allowing Ca2+to enter the cells and, as a second messenger, to set in motionclosing processes. Key words: Abscisic acid, calcium, guard cell protoplasts, stomata 相似文献
6.
Cui XL Jin WW Ding YX Alexander LD Hopfer U Douglas JG 《American journal of physiology. Cell physiology》2000,279(2):C403-C409
Previous work from this laboratorydemonstrated that arachidonic acid activates c-junNH2-terminal kinase (JNK) through oxidative intermediatesin a Ca2+-independent manner (Cui X and Douglas JG.Arachidonic acid activates c-jun N-terminal kinase throughNADPH oxidase in rabbit proximal tubular epithelial cells. ProcNatl Acad Sci USA 94: 3771-3776, 1997.). We now report thatJNK can also be activated via a Ca2+-dependent mechanism byagents that increase the cytosolic Ca2+ concentration(Ca2+ ionophore A23187, Ca2+-ATPaseinhibitor thapsigargin) or deplete intracellular Ca2+stores [intracellular Ca2+ chelator1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid(BAPTA)-AM]. The activation of JNK by BAPTA-AM occurs despite adecrease in cytosolic Ca2+ concentration as detected by theindicator dye fura 2, but appears to be related to Ca2+metabolism, because modification of BAPTA with two methyl groups increases not only the chelation affinity for Ca2+, butalso the potency for JNK activation. BAPTA-AM stimulates Ca2+ influx across the plasma membrane, and the resultinglocal Ca2+ increases are probably involved in activation ofJNK because Ca2+ influx inhibitors (SKF-96365, nifedipine)and lowering of the free extracellular Ca2+ concentrationwith EGTA reduce the BAPTA-induced JNK activation. 相似文献
7.
Inhibition of Ion Transport in Excised Barley Roots by Abscisic Acid; Relation to Water Permeability of the Roots 总被引:4,自引:0,他引:4
Previous papers have shown that abscisic acid can inhibit transportof ions across the root to the xylem vessels, resulting in reducedexudation from excised roots or inhibiting guttation from intactplants. However, it has not been established whether the inhibitionwas due to a reduction in salt transport (Js) or in permeabilityof the roots to water (Lp). This paper investigates the effectof ABA on Lp and Js separately. It is shown that Lp increasedin ABA and then fell, but was about the same as in control rootswhen transport was inhibited. The effect of ABA on exudationtherefore appeared to be mainly due to reduction in Js. Inhibitionof Js was also present in intact, transpiring plants and sowas not due to reduced water flow. The inhibition of ion releaseto the xylem affected Na+, Mg2+, Ca2+, and phosphate as wellas the major ion in the exudate, K+. It is concluded that ABAinhibits salt transport to the shoot by acting on ion transportinto the xylem, and not by reducing water flow coupled withsalt transport. 相似文献
8.
Wheat (Triticum aestivum L.) embryos form in dynamically-regulatedovular environments. Our objectives were to improve developmentof cultured immature wheat embryos by simulating, in vitro,abscisic acid (ABA) levels and O2 tensions as found in wheatovules during zygotic embryogenesis. We characterized from intactwheat kernels embryo respiration, embryo morphology and embryoand endosperm + ABA levels at 13, 19 and 25 d post-anthesis(DPA). Young (13 DPA) embryos were then excised and culturedin vitro, where they were exposed to 0·2 or 2·Ommol m3 ±ABA and 2.·1, 2·5 or 7·4mol m3 (6, 7 and 21%, respectively) gaseous O2. At 6and 12 d in culture, + ABA levels, embryo respiration and embryomorphology were characterized by treatment. Thirteen-day-oldembryos from two different plant populations differed by 17-foldin initial ABA content. However, this difference did not affectprecocious germination in vitro, nor did it affect the amountof exogenous ABA required to reduce precocious germination by40%. In this respect, embryos from both populations were equallysensitive to exogenous ABA. Cavity sap O2 levels (2·1to 2·5 mol m3) were much more effective in preventingprecocious germination of cultured embryos than were cavitysap levels of ABA (0·2 to 2·0 mmol m3).The combination of physiological levels of both ABA and O2 largelynormalized DW accumulation and embryo morphology without alteringendogenous + ABA levels. Residual respiration of cultured embryoswas higher than that of embryos grown in situ, and was not influencedby the exogenous O2 and ABA treatments Key words: Abscisic acid, embryo development, oxygen tensions, respiration, wheat 相似文献
9.
Yu X Chen XW Zhou P Yao L Liu T Zhang B Li Y Zheng H Zheng LH Zhang CX Bruce I Ge JB Wang SQ Hu ZA Yu HG Zhou Z 《American journal of physiology. Cell physiology》2007,292(3):C1147-C1155
The hyperpolarization-activated, cyclic nucleotide-gated (HCN) channels, or cardiac (If)/neuronal (Ih) time- and voltage-dependent inward cation current channels, are conventionally considered as monovalent-selective channels. Recently we discovered that calcium ions can permeate through HCN4 and Ih channels in neurons. This raises the possibility of Ca2+ permeation in If, the Ih counterpart in cardiac myocytes, because of their structural homology. We performed simultaneous measurement of fura-2 Ca2+ signals and whole cell currents produced by HCN2 and HCN4 channels (the 2 cardiac isoforms present in ventricles) expressed in HEK293 cells and by If in rat ventricular myocytes. We observed Ca2+ influx when HCN/If channels were activated. Ca2+ influx was increased with stronger hyperpolarization or longer pulse duration. Cesium, an If channel blocker, inhibited If and Ca2+ influx at the same time. Quantitative analysis revealed that Ca2+ flux contributed to 0.5% of current produced by the HCN2 channel or If. The associated increase in Ca2+ influx was also observed in spontaneously hypertensive rat (SHR) myocytes in which If current density is higher than that of normotensive rat ventricle. In the absence of EGTA (a Ca2+ chelator), preactivation of If channels significantly reduced the action potential duration, and the effect was blocked by another selective If channel blocker, ZD-7288. In the presence of EGTA, however, preactivation of If channels had no effects on action potential duration. Our data extend our previous discovery of Ca2+ influx in Ih channels in neurons to If channels in cardiac myocytes. calcium ion flux; hyperpolarization-activated, cyclic nucleotide-gated/cardiac time- and volume-dependent cation current channels 相似文献
10.
Differing temporal roles of Ca2+ and cAMP in nicotine-elicited elevation of tyrosine hydroxylase mRNA 总被引:1,自引:0,他引:1
Gueorguiev Volodia D.; Zeman Richard J.; Hiremagalur Bhargava; Menezes Ana; Sabban Esther L. 《American journal of physiology. Cell physiology》1999,276(1):C54
The involvement of cAMP- andCa2+-mediated pathways in theactivation of tyrosine hydroxylase (TH) gene expression by nicotine wasexamined in PC-12 cells. ExtracellularCa2+ and elevations inintracellular Ca2+ concentration([Ca2+]i)were required for nicotine to increase TH mRNA. The nicotine-elicited rapid rise in[Ca2+]iwas inhibited by blockers of either L-type or N-type, and to a lesserextent P/Q-, but not T-type, voltage-gatedCa2+ channels. With continualnicotine treatment,[Ca2+]ireturned to basal levels within 3-4 min. After a lag of~5-10 min, there was a smaller elevation in[Ca2+]ithat persisted for 6 h and displayed different responsiveness toCa2+ channel blockers. This secondphase of elevated[Ca2+]iwas blocked by an inhibitor of store-operatedCa2+ channels, consistent with theobserved generation of inositol trisphosphate.1,2-Bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid-AM (BAPTA-AM), when added before or 2 h after nicotine,prevented elevation of TH mRNA. Nicotine treatment significantly raised cAMP levels. Addition of the adenylyl cyclase inhibitor2',5'-dideoxyadenosine (DDA) prevented thenicotine-elicited phosphorylation of cAMP response element bindingprotein. DDA also blocked the elevation of TH mRNA only when addedafter the initial transient rise in [Ca2+]iand not after 1 h. This study reveals that several temporal phases areinvolved in the induction of TH gene expression by nicotine, each ofthem with differing requirements forCa2+ and cAMP. 相似文献
11.
Modulation of K+ channels by arachidonic acid in T84 cells. I.Inhibition of the Ca2+-dependent K+ channel 总被引:1,自引:0,他引:1
Devor Daniel C.; Frizzell Raymond A. 《American journal of physiology. Cell physiology》1998,274(1):C138
TheCl secretory response ofcolonic cells to Ca2+-mediatedagonists is transient despite a sustained elevation of intracellular Ca2+. We evaluated the effects ofsecond messengers proposed to limit Ca2+-mediatedCl secretion on thebasolateral membrane,Ca2+-dependentK+ channel(KCa) in colonic secretorycells, T84. Neither protein kinase C (PKC) nor inositoltetrakisphosphate (1,3,4,5 or 3,4,5,6 form) affectedKCa in excised inside-out patches.In contrast, arachidonic acid (AA; 3 µM) potently inhibitedKCa, reducingNPo, the productof number of channels and channel open probability, by 95%. Theapparent inhibition constant for this AA effect was 425 nM. AAinhibited KCa in the presence ofboth indomethacin and nordihydroguaiaretic acid, blockers of thecyclooxygenase and lipoxygenase pathways. In the presence of albumin,the effect of AA on KCa wasreversed. A similar effect of AA was observed onKCa during outside-out recording.We determined also the effect of thecis-unsaturated fatty acid linoleate,the trans-unsaturated fatty acidelaidate, and the saturated fatty acid myristate. At 3 µM, all ofthese fatty acids inhibited KCa,reducing NPo by 72-86%. Finally, the effect of the cytosolic phospholipaseA2 inhibitorarachidonyltrifluoromethyl ketone(AACOCF3) on thecarbachol-induced short-circuit current(Isc) responsewas determined. In the presence ofAACOCF3, the peakcarbachol-inducedIsc response wasincreased ~2.5-fold. Our results suggest that AA generation inducedby Ca2+-mediated agonists maycontribute to the dissociation observed between the rise inintracellular Ca2+ evoked by theseagonists and the associatedCl secretory response. 相似文献
12.
Cytosolic calcium concentrations (Cai) of barley aleurone protoplasts after stimulation with the plant hormone abscisic acid (ABA) were measured by using the calcium-sensitive fluorescent dye Indo-1. The measured basal Cai is about 200 nM. Stimulation with ABA induces a strong dose-dependent decrease in Cai to a minimal value of about 50 nM. This decrease occurs within 5 s. The Ca2+ antagonists La3+ and Cd2+ inhibit the ABA-induced Cai decrease in a dose-dependent manner, while the Ca2+ channel blockers verapamil and nifedipine give no inhibition. The induction of Cai decrease by ABA is consistent with activation of the plasma membrane Ca2(+)-ATPase by ABA. The possible role of this ABA-induced Cai decrease in ABA signal transduction and in counteracting the effects of gibberellic acid are discussed. 相似文献
13.
Hydrogen peroxide generated by copper amine oxidase is involved in abscisic acid-induced stomatal closure in Vicia faba 总被引:1,自引:0,他引:1
H2O2 is an essential signal in absicic acid (ABA)-induced stomatalclosure. It can be synthesized by several enzymes in plants.In this study, the roles of copper amine oxidase (CuAO) in H2O2production and stomatal closure were investigated. ExogenousABA stimulated apoplast CuAO activity, increased H2O2 productionand [Ca2+]cyt levels in Vicia faba guard cells, and inducedstomatal closure. These processes were impaired by CuAO inhibitor(s).In the metabolized products of CuAO, only H2O2 could inducestomatal closure. By the analysis of enzyme kinetics and polyaminecontents in leaves, putrescine was regarded as a substrate ofCuAO. Putrescine showed similar effects with ABA on the regulationof H2O2 production, [Ca2+]cyt levels, as well as stomatal closure.The results suggest that CuAO in V. faba guard cells is an essentialenzymatic source for H2O2 production in ABA-induced stomatalclosure via the degradation of putrescine. Calcium messengeris an important intermediate in this process. Key words: Abscisic acid, calcium, copper amine oxidase, hydrogen peroxide, putrescine, stomatal closure, Vicia faba
Received 13 October 2007; Revised 16 December 2007 Accepted 20 December 2007 相似文献
14.
The objective of this work was to test whether Ca2+, a second messenger in stress response, is involved in ABA-induced antioxidant enzyme activities in Stylosanthes guianensis. Plants were sprayed with abscisic acid (ABA), calcium channel blocker, LaCl3, calcium chelator, ethylene glycol-bis(β-amino ethyl ether)-N,N,N′, N′-tetraacetid acid (EGTA), and ABA in combination with LaCl3 or EGTA. Their effects on superoxide dismutase (SOD) and ascorbate peroxidase (APX) activities and chilling resistance were
compared. The results showed that ABA decreased electrolyte leakage and lipid peroxidation but increased maximum photochemical
efficiency measured as variable to maximum fluorescence ratio (Fv/Fm) under chilling stress. Treatment with LaCl3 or EGTA alone and in combination with ABA increased electrolyte leakage and lipid peroxidation, decreased Fv/Fm, suggesting
that the block in Ca2+ signalling decreased chilling resistance of S. guianensis and the ABA-enhanced chilling resistance. ABA-induced SOD and APX activities were suppressed by LaCl3 or EGTA. The results suggested that Ca2+ is involved in the ABA-enhanced chilling resistance and the ABA-induced SOD and APX activities in S. guianensis. 相似文献
15.
The conversion of 1-aminocyclopropane 1-carboxylic acid (ACC) to ethylene by hypocotyl segments of sunflower (Helianthus annuus L.) seedlings was inhibited by abscisic acid (ABA) and methyl jasmonate (Me-Ja), and this inhibitory effect increased with increasing concentration of both growth regulators. On the contrary, CaCl, enhanced ACC conversion to ethylene at the concentrations of 10-4 M and 5 x 10-4 M, however lower and higher concentrations had no significant action. CaCl, (5 x 10-4M) seemed to magnify the inhibition of the reaction induced by ABA, whereas it reduced (5 x 10-4M) and even abolished (10-3M) the inhibitory action of Me-Ja. The results obtained with a Ca2+ chelator (EGTA), a Ca2+ channel blocker (nifedipine) and calmodulin antagonists (W7 and TFP), given in association with ABA or Me-Ja, suggested that calcium was involved in the inhibition of ACC conversion to ethylene by ABA and Me-Ja through an interaction with calmodulin. However, the mechanism of action of the two growth regulators seemed to be different, since all treatments which resulted in a decrease in cytosolic Ca2+ concentration or in calmodulin action induced a decrease in the effect of ABA and an increase in the effect of Me-Ja.Abbreviations ABA
abscisic acid
- ACC
1-aminocyclopropane 1-carboxylic acid
- EFE
ethylene for enzyme
- EGTA
ethylene glycol-bis-2-aminoethyl tetraacetic acid
- Me-Ja
methyl jasmonate
- NIF
nifedipine
- TFP
trifluoperazine dihydrochloride
- W7
N-(6-aminohexyl)5-chloro-l-naphthalenesulfonamide hydrochloride 相似文献
16.
Phototropins (phot1 and phot2) are blue light (BL) receptorsthat mediate responses including phototropism, chloroplast movementand stomatal opening, and increased cytosolic Ca2+. BL absorbedby phototropins activates plasma membrane H+-ATPase in guardcells, resulting in membrane hyperpolarization, and drives K+uptake and stomatal opening. However, it is unclear whetherthe phototropin-mediated Ca2+ increase activates the H+-ATPase.Here, we determined cytosolic Ca2+ concentrations in guard cellprotoplasts (GCPs) from Arabidopsis transformed with aequorin.Cytosolic Ca2+ increased rapidly in response to BL in GCPs fromboth the wild type and phot1 phot2 double mutants, but was mostlysuppressed by an inhibitor of photosynthetic electron flow (DCMU).With depleted external K+, we observed another slower Ca2+ increase,which was phototropin- dependent. Fusicoccin, a H+-ATPase activator,mimicked the effect of BL. The slow Ca2+ increase thus appearsto result from membrane hyperpolarization. The slow Ca2+ increasewas suppressed by external K+ and was restored by blockers ofinward-rectifying K+ channels, CsCl and tetraethylammonium,suggesting the preferential uptake of K+ over Ca2+. Such efficientK+ uptake in response to BL was not found in mesophyll cells.Both the fast and the slow Ca2+ increases were inhibited byCa2+ channel blockers (CoCl2 and LaCl3) and a chelating agent(EGTA). These results indicate that the phototropin-mediatedCa2+ increase was not observed prior to H+-ATPase activationin guard cells and that Ca2+ entered guard cells via Ca2+ channelsthrough photosynthesis and phototropin-mediated membrane hyperpolarization. 相似文献
17.
We isolated a mutant from Vicia faba L. cv. House Ryousai. Itwilts easily under strong light and high temperature conditions,suggesting that its stomatal movement may be disturbed. We determinedresponses of mutant guard cells to some environmental stimuli.Mutant guard cells demonstrated an impaired ability to respondto ABA in 0.1 mM CaCl2 and stomata did not close in thepresence of up to 1 mM ABA, whereas wild-type stomata closedwhen exposed to 10 µM ABA. Elevating external Ca2+caused a similar degree of stomatal closure in the wild typeand the mutant. A high concentration of CO2 (700 µlliter1) induced stomatal closure in the wild type, butnot in the mutant. On the basis of these results, we proposethe working hypothesis that the mutation occurs in the regiondownstream of CO2 and ABA sensing and in the region upstreamof Ca2+ elevation. The mutant is named fia (fava bean impairedin ABA-induced stomatal closure).
3 Corresponding author: E-mail, smoiwai{at}agri.kagoshima-u.ac.jp;Fax, +81-99-285-8556. 相似文献
18.
Activation of chloride currents in murine portal vein smooth muscle cells by membrane depolarization involves intracellular calcium release 总被引:3,自引:0,他引:3
The present study describes the first characterization of Ca2+-activated Cl currents (IClCa) in single smooth muscle cells from a murine vascular preparation (portal veins). IClCa was recorded using the perforated patch version of the whole cell voltage-clamp technique and was evoked using membrane depolarization. Generation of IClCa relied on Ca2+ entry through dihydropyridine-sensitive Ca2+ channels because IClCa was abolished by 1 µM nicardipine and enhanced by raising external Ca2+ concentration or by application of BAY K 8644. IClCa was characterized by the sensitivity to Cl channel blockers and the effect of altering the external anion on reversal potential. Activation of IClCa after membrane depolarization was dependent on Ca2+ release from intracellular stores. Thus the amplitude of IClCa was diminished by the SR-ATPase inhibitor cyclopiazonic acid, the inositol 1,4,5-trisphosphate receptor antagonist 2-aminoethoxydiphenyl borate (2-APB), and the ryanodine receptor blocker tetracaine. The degree of inhibition produced by the application of 2-APB and tetracaine together was significantly greater than the effect of each agent applied alone. In current-clamp mode, injection of depolarizing current elicited a biphasic action potential, with the later depolarization being sensitive to niflumic acid (NFA; 10 µM). In isometric tension recordings, NFA inhibited spontaneous contractions. These data support a role for this conductance in portal vein excitability. 相似文献
19.
Lee S Kim JC Li Y Son MJ Woo SH 《American journal of physiology. Cell physiology》2008,294(4):C966-C976
This study examines whether fluid pressure (FP) modulates the L-type Ca2+ channel in cardiomyocytes and investigates the underlying cellular mechanism(s) involved. A flow of pressurized (16 dyn/cm2) fluid, identical to that bathing the myocytes, was applied onto single rat ventricular myocytes using a microperfusion method. The Ca2+ current (ICa) and cytosolic Ca2+ signals were measured using a whole cell patch-clamp and confocal imaging, respectively. It was found that the FP reversibly suppressed ICa (by 25%) without altering the current-voltage relationships, and it accelerated the inactivation of ICa. The level of ICa suppression by FP depended on the level and duration of pressure. The Ba2+ current through the Ca2+ channel was only slightly decreased by the FP (5%), suggesting an indirect inhibition of the Ca2+ channel during FP stimulation. The cytosolic Ca2+ transients and the basal Ca2+ in field-stimulated ventricular myocytes were significantly increased by the FP. The effects of the FP on the ICa and on the Ca2+ transient were resistant to the stretch-activated channel inhibitors, GsMTx-4 and streptomycin. Dialysis of myocytes with high concentrations of BAPTA, the Ca2+ buffer, eliminated the FP-induced acceleration of ICa inactivation and reduced the inhibitory effect of the FP on ICa by 80%. Ryanodine and thapsigargin, abolishing sarcoplasmic reticulum Ca2+ release, eliminated the accelerating effect of FP on the ICa inactivation, and they reduced the inhibitory effect of FP on the ICa. These results suggest that the fluid pressure indirectly suppresses the Ca2+ channel by enhancing the Ca2+-induced intracellular Ca2+ release in rat ventricular myocytes. L-type Ca2+ current; fluid pressure; ventricular myocytes; cytosolic Ca2+ transient 相似文献
20.
The effect of Ca2+ and ammonia on mitochondrial NADH-glutamatedehydrogenase (GDH: EC 1.4.1.2
[EC]
) isolated from turnip root (Brassicarapa L.) activity was examined. Increasing the ammonia [(NH4)2SO4]concentration led to significant substrate inhibition whichcould be reversed by micromolar levels of Ca2+. The sensitivityof the enzyme to ammonia inhibition and its reversal by Ca2+was affected by proteolysis. After treatment with various proteases,lower concentrations of Ca2+ were capable of fully activatingthe enzyme or overcoming the inhibitory effects of high ammonium,compared to non-treated enzyme. However, the protease-treatedenzyme was still sensitive to ethylene glycol-bis(ß-aminoethylether) N,N,N',N'-tetraacetate (EGTA). In contrast, NADH-GDHactivity was inhibited approx. 30% by organic mercurials (200µm), but the residual activity was not affected by thesubsequent additions of EGTA. NADH-GDH activity could also bestimulated by additions of high concentrations of NaCl (300mM) in the absence of added Ca2+. These results suggest thathydrophobic and -SH groups may be involved in the regulationof mitochondrial NADH-GDH activity by Ca2+.
2 Present address: CSIRO Division of Horticulture, Urrbrae,S.A. 5064, Australia (Received April 18, 1990; Accepted July 23, 1990) 相似文献