共查询到20条相似文献,搜索用时 15 毫秒
1.
Yamaya Tomoyuki; Tanigawa Motokazu; Konno Haruyoshi; Matsumoto Hideaki 《Plant & cell physiology》1982,23(7):1175-1184
In Ca2$-starved cucumber roots, about 23% of phosphatase assayedat pH 9.0 (ALPase) in the crude cell walls was solubilized witheither 2 M NaCl or purified endo type polygalacturonase (endo-PG)from yeast culture broth. Coexistence of NaCl and endo-PG hadlittle effect on further release of ALPase, and a small amountof the activity was solubilized from the NaCl-pretreated cellwalls by incubation with endo-PG. Ionically bound ALPase, therefore,seemed to be localized in the fraction which was hydrolyzedby endo-PG in the crude cell walls of Ca2$-starved cucumberroots. In the control roots, however, ALPase was not effectivelysolubilized by the treatment with endoPG. Ca2$ starvation reducedthe contents of rhamnose, uronic acids and galactose among non-cellulosicsugars in the cell walls, suggesting that the structure of pecticsubstances, possibly rhamnogalacturonan, is altered during thestarvation. Activities of both ionically and covalently bound ALPases greatlyincreased during Ca2$ starvation. The increased ALPase in theNaCl-solubilized fraction hydrolyzed most phosphate esters tested,whereas the enzyme from control roots only cleaved nucleoside2'(3')-monophosphates and p-nitrophenylphosphate. Differencesin the properties between both types of roots were also foundwhen the effects of various inhibitors were tested. Profilesof ALPase-isozymes after polyacrylamide gel electrophoresiswere also altered by Ca2$ starvation. (Received June 2, 1982; Accepted July 20, 1982) 相似文献
2.
Proton extrusion from cucumber roots decreased markedly duringCa2+ starvation in the presence of KC1. Vesicles with ATP-dependentproton transport activity were prepared from the microsomalmembrane fraction of control and Ca2+-starved roots. The protontransport rate of the vesicles from Ca2+-starved roots was repressedto less than half of the vesicles prepared from the controlroots. K+-Mg2+-ATPase activity associated with the vesiclesprepared from Ca2+-starved roots was approximately one-thirdof the activity associated with those prepared from controlroots. Km values of the proton transport rate and K+-Mg2+-ATPasefor ATP were much higher in vesicles prepared from Ca2+-starvedroots. The repression of proton extrusion linked with K+ uptake inthe Ca2+-starved roots could be largely caused by the reducedproton pumping activity associated with microsomal membranesin the roots. (Received May 25, 1987; Accepted October 14, 1987) 相似文献
3.
The ATPase activity of the plasma membrane-enriched fractionwas severely inhibited by withdrawal of Ca2+ from the mediumfor 5 days, although the root system appeared to be unaffectedto visual inspection. Partially lipid-depleted ATPases withsimilar ratios of phospholipid to protein were prepared fromthe plasma membrane-enriched fraction of cucumber roots culturedwith control medium and one lacking Ca2+, and their propertieswere compared. SDS disc polyacrylamide gel electrophoresis showedthat the polypeptide components were essentially similar betweencontrol and Ca2+-starved roots. Partially lipid-depleted ATPasereassociated with asolectin, the lecithin from soybean, showedtypical characteristics of plasma membrane type ATPase; pH optimumat 6.5, high specificity for ATP as substrate and strong inhibitionby vanadate but not nitrate. The activity of reassociated ATPaseobtained from the control roots was apparently higher than theactivity obtained from Ca2+-starved roots. The amount of asolectinrequired for maximum activation of the partially lipid-depletedATPase prepared from control roots was much lower than thatprepared from Ca2+-starved roots. Reassociation of partiallylipid-depleted ATPase with asolectin produced higher ATPaseactivity than that with individual phospholipids. The activationof partially lipid-depleted ATPase prepared from control rootswith asolectin was not inhibited by addition of a sample preparedfrom Ca2+-starved roots. Thus, a decrease in the functionalassociation of ATPase with phospholipids might be one of thephysiological injuries in root cell membranes of cucumber causedby Ca2+ starvation.
1Permanent address: Department of Horticulture, College of Agriculture,Chonnam National University, Chonnam 500, Korea. (Received February 23, 1988; Accepted August 18, 1988) 相似文献
4.
The uptake of K+ by cucumber plants decreased markedly duringCa2+ starvation. A plasma membrane-enriched fraction, judgedfrom the distribution of marker enzymes, was prepared from controland Ca2+-starved roots. The Mg2+- and K+-Mg2+-ATPase activitiesassociated with the plasma membrane-enriched fraction of controlroots were maxima at pH 6.5. Various monovalent cations andpotassium salts of monovalent anions stimulated Mg2+-ATPaseactivity. Vanadate, DES and DCCD inhibited K+- Mg2+-ATPase activity.Of the divalent cations and phosphate esters tested, Mg2+ andATP were most effective for the stimulation of ATPase by K+,whereas Ca2+ was ineffective in replacing Mg2+. Mg2+- and K+-Mg2+-ATPase activities associated with the plasmamembrane enriched fraction of Ca2+-starved roots were much lowerthan those of control roots. Km values of K+-Mg2+-ATPase forATP were comparable for control and Ca2+-starved roots. The K+-stimulated activity of Mg2+-ATPase in Ca2+-starved rootswas approximately one fourth that of the control, whereas therate of stimulation was only slightly lower in Ca2+-starvedroots. (Received May 9, 1984; Accepted September 17, 1984) 相似文献
5.
In apple fruit, active ATP-dependent microsomal Ca2$ uptakeand respiration-dependent mitochondrial Ca2$ uptake were observed. The mitochondrial Ca2$ uptake was depressed by the calmodulinantagonists chlorpromazine hydrochloride (CPZ) and N-(6-aminohexyl)-5-chloro-1-naphthalene-sulfonamidehydrochloride (W-7). The Ca2$-ATPase from apple mitochondriawas also inhibited by CPZ or W-7. The apparent Km value forCa2$ in mitochondrial Ca2$ uptake (Km=0.35 mM) was similar tothat of mitochondrial Ca2$-ATPase (Km=0.32 mM). The inhibitoryeffect of W-7 on the activity of the mitochondrial Ca2$ uptakewas closely correlated with the inhibition by W-7 of mitochondrialCa2$-ATPase (r=0.996). These findings indicate that the mitochondrialuptake of Ca2$ in apple fruit depends on the calmodulin-mediatedactivation of Ca2$-ATPase. The microsomal Ca2$ uptake was depressed by CPZ, suggestingthat the microsomal Ca2$ uptake may also be modulated by calmodulin.
1 Contribution No. C-72, Fruit Tree Research Station. (Received June 7, 1982; Accepted October 19, 1982) 相似文献
6.
This paper examines the relationship between the ability ofsubterranean clover to use P-esters as sources of P for growth,and the enzymatic hydrolysis of those P-esters at the root surface.Trifolium subterraneum (cv. Mt. Barker) was grown under sterileconditions in porous agar containing either KH2PO4 (P1), 2',3'-cyclicadenosine monophosphate (cAMP) or inositol hexaphosphate (IHP)as the source of P in the medium. Subterranean clover used cAMPas well as P1 as a source of P for growth, but made little useof IHP. This preference in the use of P-esters was associatedwith differences in the substrate specificities of the externallyaccessible root phosphatases; roots of P-deficient clover grownunder sterile conditions had high hydrolytic activity againstcAMP but not IHP. These results are discussed in terms of anhypothesis on the function of the externally accessible phosphatases,i.e. that the phosphatases are present to recapture P from organicP compounds leaked from the cells. Key words: Organic P, extracellular phosphatase, roots, P uptake, clover 相似文献
7.
Glutamate dehydrogenase (GDH) (EC 1.4.1.3
[EC]
.) purified from greentobacco callus mitochondria was activated markedly by Ca2$ inthe amination reaction. This activation was detectable evenat concentrations below 5 µM Ca2$. Saturation curves for the three substrates of the aminationreaction showed normal Michaelis-Menten kinetics in the presenceof 1 mM of Ca2$, but pronounced substrate inhibition occurredwithout Ca2$. The effect of Ca2$ was chiefly on the maximalvelocity. The saturation curve for NH4Cl in the presence of Ca2$ was modulatedby a change in pH. The apparent Km value for NH4Cl markedlydecreased whereas that for -ketoglutarate increased slightlywhen the pH was raised from 7.3 to 9.0. In contrast, the Kmfor NADH was little affected by raising the pH. The characteristicof GDH which increases its affinity for NH4Cl when the pH israised may be compatible with the detoxification of ammonia.
1 Present address: Mochida Pharmaceutical Co., Ltd. (Received August 24, 1981; Accepted November 28, 1981) 相似文献
8.
Chromatin-associated nucleoside triphosphate diphosphatase (NTDPase)activity was detected in Alaska pea plant only at the germinationstage in a study of the plant's development over 5 month fromthe dormant to fruiting stages. This enzyme activity was alsodetected in seedlings of several dicotyledonous plants includingsoybean, Usui pea, cowpea and cucumber, but almost none wasfound in monocotyledonous corn and rice plants. When the chromatin of pea epicotyl was fractionated into template-activeand -inactive forms by DNase II digestion, most of the NTDPaseactivity was found in the active chromatin. A new method to rapidly isolate and purify NTDPase from peaepicotyl chromatin was developed in which NTDPase was elutedwith a linear gradient of NaCl on a column packed with cellulosepowder and chromatin. DNA remained on the column and the elutedNTDPase was purified further by chromatography using trimethylamino-2-hydroxypropylcellulose (TMAP-cellulose) and a Sephadex G-100 column, whichgive chromatin 18-fold purer than the starting sample. This purified NTDPase was adsorbed by DNA-cellulose, which isfurther evidence that NTDPase is a kind of non-histone proteinassociated with DNA. Several cations including Ca2$, Mg2$, Mn2$and Zn2$ stimulated the enzyme activity, with the maximal eightfoldactivation by Ca2$. NTDPase activity was clearly inhibited byKCN and pyrophosphate, but not by SH-blocking inhibitors andvarious metal chelators at 1 mM. 相似文献
9.
Vela J Pérez-Millán MI Becu-Villalobos D Díaz-Torga G 《American journal of physiology. Cell physiology》2007,293(3):C951-C959
The L-type Ca2+ channel is the primary voltage-dependent Ca2+-influx pathway in many excitable and secretory cells, and direct phosphorylation by different kinases is one of the mechanisms involved in the regulation of its activity. The aim of this study was to evaluate the participation of Ser/Thr kinases and tyrosine kinases (TKs) in depolarization-induced Ca2+ influx in the endocrine somatomammotrope cell line GH3. Intracellular Ca2+ concentration ([Ca2+]i) was measured using a spectrofluorometric method with fura 2-AM, and 12.5 mM KCl (K+) was used as a depolarization stimulus. K+ induced an abrupt spike (peak) in [Ca2+]i that was abolished in the presence of nifedipine, showing that K+ enhances [Ca2+]i, preferably activating L-type Ca2+ channels. H89, a selective PKA inhibitor, significantly reduced depolarization-induced Ca2+ mobilization in a concentration-related manner when it was applied before or after K+, and okadaic acid, an inhibitor of Ser/Thr phosphatases, which has been shown to regulate PKA-stimulated L-type Ca2+ channels, increased K+-induced Ca2+ entry. When PKC was activated by PMA, the K+-evoked peak in [Ca2+]i, as well as the plateau phase, was significantly reduced, and chelerythrine (a PKC inhibitor) potentiated the K+-induced increase in [Ca2+]i, indicating an inhibitory role of PKC in voltage-dependent Ca2+ channel (VDCC) activity. Genistein, a TK inhibitor, reduced the K+-evoked increase in [Ca2+]i, but, unexpectedly, the tyrosine phosphatase inhibitor orthovanadate reduced not only basal Ca2+ levels but, also, Ca2+ influx during the plateau phase. Both results suggest that different TKs may act differentially on VDCC activation. Activation of receptor TKs with epidermal growth factor (EGF) or vascular endothelial growth factor potentiated K+-induced Ca2+ influx, and AG-1478 (an EGF receptor inhibitor) decreased it. However, inhibition of the non-receptor TK pp60 c-Src enhanced K+-induced Ca2+ influx. The present study strongly demonstrates that a complex equilibrium among different kinases and phosphatases regulates VDCC activity in the pituitary cell line GH3: PKA and receptor TKs, such as vascular endothelial growth factor receptor and EGF receptor, enhance depolarization-induced Ca2+ influx, whereas PKC and c-Src have an inhibitory effect. These kinases modulate membrane depolarization and may therefore participate in the regulation of a plethora of intracellular processes, such as hormone secretion, gene expression, protein synthesis, and cell proliferation, in pituitary cells. phosphatases; protein kinase A; protein kinase C; epidermal growth factor 相似文献
10.
The movement of calcium across the elongation zone of gravistimulatedprimary roots of maize (Zea mays L.) was measured using 45Ca2$.Radioactive calcium was applied to one side of the elongationzone about 4 mm back from the root tip and the distributionof radioactivity across the root in the region of applicationwas determined using scintillation spectrometry. The movementof 45Ca2$ across the elongation zone was non-polar in verticallyoriented roots. In gravistimulated roots the movement of labelwas polarized with about twice as much label moving from topto bottom as from bottom to top. A variety of treatments whichinterfere with gravitropism was found to eliminate the polarmovement of 45Ca2$ across the elongation zone. In maize cultivarswhich require light for gravitropic competency, dark grown rootsexhibited neither gravitropism nor polar movement of 45Ca2$across the elongation zone. Upon illumination the roots developedboth gravitropic competency and gravity-induced polar movementof 45Ca2$ across the elongation zone. Similarly, roots of light-grownseedlings lost both gravitropic competency and 45Ca2$ transportpolarity upon transfer to the dark. The results indicate a closecorrelation between calcium movement and gravitropism in primaryroots of maize. (Received July 20, 1985; Accepted September 25, 1985) 相似文献
11.
Activity of glucose 6-phosphate dehydrogenase (D-glucose 6-phosphate:NADP oxidoreductase, EC 1.1.1.49
[EC]
) preparation from sweet potatoroot tissue was markedly altered in the presence of variousions. Cations or anions were effective in the following order:Na$, K$>Tris$>NH4$>Mg2$>Ca2$, or Cl>NO3,HPO42>SO42>HCO3. Activity was inhibitedat high concentrations of Ca2$, and HCO3,. In an investigationon the dependence of the activity on pH, two activity peakswere clearly observed at low ionic strength. Ionic strength altered both the Km and Vmax for glucose 6-phosphate(G6P). A Lineweaver-Burk plot for the enzyme, with respect toG6P, showed a bimodal nature at low ionic strength; suggestingnegative cooperativity. Deviation from linearity of the plotwas less with an increase in the ionic strength.
1 Present address: Institute of Applied Microbiology, Universityof Tokyo, Bunkyo-ku, Tokyo 113. (Received September 18, 1971; ) 相似文献
12.
Long-Term Phosphate Starvation and Respiratory Metabolism in Suspension-Cultured Catharanthus roseus Cells 总被引:1,自引:0,他引:1
In order to clarify the metabolic adaptation of respiratorypathways in plants to limited levels of Pi, the effects of long-termstarvation of Pi on the activities of various enzymes relatedto respiratory metabolism were examined in suspension-culturedCatharanthus roseus cells. When the activities were expressedas units per g fresh weight, only those of phosphoenolpyruvate-hydrolyzing(PEP-hydrolyzing) enzyme (which may possibly be equivalent tothe acid phosphatase activity derived from vacuoles) and PEPcarboxylase were higher in the Pi-starved cells than in controlcells. Activities of other enzymes in the Pi-starved cells werelower than or similar to those of the control cells. Time-coursestudies indicated that PEP-hydrolyzing activity was inducibleby starvation of Pi. However, in contrast to the results reportedby Duff et al. [(1989a) Plant Physiol. 90: 1275.], fluctuationsin the activity of PP1:fructose-6-phosphate 1-phosphotransferaseduring starvation of Pi were similar to those in levels of phosphofructokinaseand 6-phosphogluconate dehydrogenase. These data suggest thatthe concept of the phosphate starvation-inducible bypasses,which are engineered via the coarse control (i.e., induction)of specified enzymes and were proposed initially by Duff etal. in Brassica nigra cells, is not directly applicable to Catharanthusroseus cells in suspension. Tracer experiments using [U-14C]glutamineindicated that a significant proportion of respiratory substratescould be supplied from the enlarged pool of amino acids duringstarvation of Pi. These assumptions are supported by the observedfluctuations in levels of free amino acids and of protein inP1-fed and P1-deficient Catharanthus roseus cells.
1Part 41 in the series Metabolic Regulation in PlantCell Cultrue
2Present Address: Morinaga Mild Industry, 5-1-83, Higashihara,Zamma-shi, Kanagawa, 228 Japan 相似文献
13.
Reactivation of photosynthetic oxygen-evolution was investigatedwith chloroplasts inhibited by 0.8 M Tris-, 0.8 M Tris-20% acetone-,0.8 M KCl-, 0.5 M NaClO4- or 1 mM NH2OH-washing, and with heat-treatedor aged chloroplasts. These chloroplasts restored oxygen evolvingactivity by two successive treatments; incubation of chloroplastswith reduced DPIP, then with Mn2$, Ca2$, dithiothreitol andbovine serum albumin under weak illumination (light-reactivation). Some factors required for light-reactivation could be omitteddepending on the inhibition treatment. For example, Mn2$, Ca2$and dithiothreitol were not necessary for (1 mM NH2OH-STN (pH7.0)-washed)-DPIP-treated chloroplasts, and dithiothreitol for(Tris-acetone (pH 8.4)-washed)-DPIP-treated chloroplasts. Uncouplers, such as atebrin, CCCP, DCCD and NH4Cl, inhibitedthe lightreactivation. The Mn and Ca contents of the chloroplasts were determined withinhibited and DPIP-treated chloroplasts. The Mn content of thechloroplasts tended to decrease with increasing pH of the washingmedium for inhibition. The Ca content decreased when chloroplastswere washed with 0.8 M KCl. (Received November 22, 1974; ) 相似文献
14.
Yamamoto Yoko; Hachiya Akiko; Hamada Hiroki; Matsumoto Hideaki 《Plant & cell physiology》1998,39(9):950-957
Aluminum (Al) enhances ferrous ion [Fe(II)]-mediated peroxidationof lipids, which is lethal to normal tobacco cells, but notto phosphate (Pi)-starved cells ( P cells). We foundthat tobacco cells accumulated phenylpropanoid compounds includingchlorogenic acid (CGA) and caffeic acid (CA) during Pi starvation.The accumulation was inhibited by 2-aminoindan-2-phosphonicacid (AIP), a specific inhibitor of L-phenylalanine ammonialyase (PAL). CGA, CA and also an extract containing the phenylpropanoidcompounds from P cells protected normal cells ( +P cells)efficiently from both lipid peroxidation and the loss of viabilitycaused by the combined application of Al and Fe(II), indicatingthat the phenylpropanoids acted as antioxidant molecules. Pcells exhibited approximately 25-fold higher specific activityof PAL than +P cells. The content of the phenylpropanoids andthe activity of PAL were not affected by the combined treatmentwith Al and Fe(II) in either +P cells or P cells. Theseresults suggest that an increase in PAL activity during Pi starvationenhances the accumulation of phenylpropanoids, and that thephenylpropanoids protect tobacco cells from cytotoxic lipidperoxidation caused by the combination of Al and Fe(II)
4CREST, Japan Science and Technology Corporation (JST). 相似文献
15.
16.
Nakamura Yoshiyuki; Kasamo Kunihiro; Sakata Makato; Ohta Eiji 《Plant & cell physiology》1992,33(2):139-149
Extrusion of protons as a response to high-NaCl stress in intactmung bean roots was investigated at different external concentrationsof Ca2+ ions ([Ca2+]ex). The extrusion of protons was graduallyenhanced in the roots exposed to 100 mM NaCl, and high [Ca2+]exdiminished this enhancement of the extrusion. Vesicles of plasmalemmaand tonoplast were prepared from the roots and the H+-translocatingATPase (H+-ATPase) activities associated with the two typesof membrane and the H+-pyrophosphatase (H+-PPase) activity ofthe tonoplast were assayed. The plasmalemma ATPase was stimulatedin parallel with dramatic increases in the intracellular concentrationof Na+([Na+]in). High [Ca2+]ex prevented the increase in [Na+]inand diminished the stimulation of ATPase activity. The tonoplastATPase showed a rapid response to salt stress and was similarlystimulated even at high [Ca2+]M. The activities of both ATPaseswere, however, insensitive to concentrations of Na+ ions upto 100 HIM. By contrast, H+-PPase activity of the tonoplastwas severely inhibited with increasing [Na+]in under salt stressand recovered with high [Ca2+]ex. These findings suggest thathigh-NaCl stress increases the intracellular concentration ofNa+ ions in mung bean roots, which inhibits the tonoplast H+-PPase,and the activity of the plasmalemma H+-ATPase is thereby stimulatedand regulates the cytoplasmic pH. (Received March 26, 1991; Accepted December 13, 1991) 相似文献
17.
Yeung HM Kravtsov GM Ng KM Wong TM Fung ML 《American journal of physiology. Cell physiology》2007,292(6):C2046-C2056
This study examined Ca2+ handling mechanisms involved in cardioprotection induced by chronic intermittent hypoxia (CIH) against ischemia-reperfusion (I/R) injury. Adult male Sprague-Dawley rats were exposed to 10% inspired O2 continuously for 6 h daily from 3, 7, and 14 days. In isolated perfused hearts subjected to I/R, CIH-induced cardioprotection was most significant in the 7-day group with less infarct size and lactate dehydrogenase release, compared with the normoxic group. The I/R-induced alterations in diastolic Ca2+ level, amplitude, time-to-peak, and the decay time of both electrically and caffeine-induced Ca2+ transients measured by spectrofluorometry in isolated ventricular myocytes of the 7-day CIH group were less than that of the normoxic group, suggesting an involvement of altered Ca2+ handling of the sarcoplasmic reticulum (SR) and sarcolemma. We further determined the protein expression and activity of 45Ca2+ flux of SR-Ca2+-ATPase, ryanodine receptor (RyR) and sarcolemmal Na+/Ca2+ exchange (NCX) in ventricular myocytes from the CIH and normoxic groups before and during I/R. There were no changes in expression levels of the Ca2+-handling proteins but significant increases in the RyR and NCX activities were remarkable during I/R in the CIH but not the normoxic group. The augmented RyR and NCX activities were abolished, respectively, by PKA inhibitor (0.5 µM KT5720 or 0.5 µM PKI14-22) and PKC inhibitor (5 µM chelerythrine chloride or 0.2 µM calphostin C) but not by Ca2+/calmodulin-dependent protein kinase II inhibitor KN-93 (1 µM). Thus, CIH confers cardioprotection against I/R injury in rat cardiomyocytes by altered Ca2+ handling with augmented RyR and NCX activities via protein kinase activation. cardioprotection; intracellular calcium 相似文献
18.
Chen L Lu XY Li J Fu JD Zhou ZN Yang HT 《American journal of physiology. Cell physiology》2006,290(4):C1221-C1229
We have previously demonstrated that intermittent high-altitude (IHA) hypoxia significantly attenuates ischemia-reperfusion (I/R) injury-induced excessive increase in resting intracellular Ca2+ concentrations ([Ca2+]i). Because the sarcoplasmic reticulum (SR) and Na+/Ca2+ exchanger (NCX) play crucial roles in regulating [Ca2+]i and both are dysfunctional during I/R, we tested the hypothesis that IHA hypoxia may prevent I/R-induced Ca2+ overload by maintaining Ca2+ homeostasis via SR and NCX mechanisms. We thus determined the dynamics of Ca2+ transients and cell shortening during preischemia and I/R injury in ventricular cardiomyocytes from normoxic and IHA hypoxic rats. IHA hypoxia did not affect the preischemic dynamics of Ca2+ transients and cell shortening, but it significantly suppressed the I/R-induced increase in resting [Ca2+]i levels and attenuated the depression of the Ca2+ transients and cell shortening during reperfusion. Moreover, IHA hypoxia significantly attenuated I/R-induced depression of the protein contents of SR Ca2+ release channels and/or ryanodine receptors (RyRs) and SR Ca2+ pump ATPase (SERCA2) and SR Ca2+ release and uptake. In addition, a delayed decay rate time constant of Ca2+ transients and cell shortening of Ca2+ transients observed during ischemia was accompanied by markedly inhibited NCX currents, which were prevented by IHA hypoxia. These findings indicate that IHA hypoxia may preserve Ca2+ homeostasis and contraction by preserving RyRs and SERCA2 proteins as well as NCX activity during I/R. intracellular Ca2+ concentration; Ca2+ transients; Ca2+ transporters; myofilament Ca2+ sensitivity 相似文献
19.
Regulation of exocytosis by purinergic receptors in pancreatic duct epithelial cells 总被引:2,自引:0,他引:2
Jung SR Kim MH Hille B Nguyen TD Koh DS 《American journal of physiology. Cell physiology》2004,286(3):C573-C579
In epithelial cells, several intracellular signals regulate the secretion of large molecules such as mucin via exocytosis and the transport of ions through channels and transporters. Using carbon fiber amperometry, we previously reported that exocytosis of secretory granules in dog pancreatic duct epithelial cells (PDEC) can be stimulated by pharmacological activation of cAMP-dependent protein kinase (PKA) or protein kinase C (PKC), as well as by an increase of intracellular free Ca2+ concentration ([Ca2+]i). In this study, we examined whether exocytosis in these cells is modulated by activation of endogenous P2Y receptors, which increase cAMP and [Ca2+]i. Low concentrations of ATP (<10 µM) induced intracellular Ca2+ oscillation but no significant exocytosis. In contrast, 100 µM ATP induced a sustained [Ca2+]i rise and increased the exocytosis rate sevenfold. The contribution of Ca2+ or cAMP pathways to exocytosis was tested by using the Ca2+ chelator BAPTA or the PKA inhibitors H-89 or Rp-8-bromoadenosine 3',5'-cyclic monophosphorothioate. Removal of [Ca2+]i rise or inhibition of PKA each partially reduced exocytosis; when combined, they abolished exocytosis. In conclusion, ATP at concentrations >10 µM stimulates exocytosis from PDEC through both Ca2+ and cAMP pathways. secretion; amperometry; photometry; calcium, adenosine 3',5'-cyclic monophosphate 相似文献
20.
SYNOPSIS. Crayfish have a long evolutionary history in temperatefresh water (FW). Ion regulation is challenged by low externalconcentrations of Na, Cl, and Ca (<1 mM). In intermolt theprimary concern is Na and Cl balance; around ecdysis the emphasisswitches to Ca regulation as the cuticle is decalcified/calcified.Compared with marine crustaceans, intermolt crayfish maintaina reduced extracellular (EC) osmolality and have lower permeabilityto both ions and water. Hyperregulation involves active branchialuptake of Na and Cl and the unique ability to produce a hypotonicurine. Ion uptake involves apical electroneutral ion exchange(Na$ for H$; Cl for HCO3; counterions providedfrom CO2 via carbonic anhydrase) followed by active basolateraltransport of Na via the Na pump, with Cl following passively.Reabsorption of 95% of filtered electrolytes at the antennalgland (kidney) involves similar subcellular mechanisms in amorphologically differentiated region of the distal tubule.Intermolt crayfish exhibit negative Ca balance (passive effluxunopposed by uptake) tolerable in view of the large cuticularCaCO3 reserve. In premolt, cuticular Ca is reabsorbed. A smallamount is stored as gastroliths, the remainder is lost via branchialexcretion and in the discarded exuviae. At ecdysis, FW uptakegenerates the physical force for shedding, leaving the crayfishwith dilute hemolymph and a Ca deficiency. Levels of EC Na andCl are restored by intensive postmolt branchial uptake. Mineralizationof the soft exoskeleton involves remobilization of stored Caand branchial uptake of Ca and HCO3. Transepithelial Ca transportinvolves Ca2$ ATPase and Ca2$/Na$ exchange. The importance ofexternal electrolytes and pH in postmolt ion regulation is explored,as are some allometric considerations. 相似文献