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1.
The choroid plexus epithelium secretes electrolytes and fluid in the brain ventricular lumen at high rates. Several channels and ion carriers have been identified as likely mediators of this transport in rodent choroid plexus. This study aimed to map several of these proteins to the human choroid plexus. Immunoperoxidase-histochemistry was employed to determine the cellular and subcellular localization of the proteins. The water channel, aquaporin (AQP) 1, was predominantly situated in the apical plasma membrane domain, although distinct basolateral and endothelial immunoreactivity was also observed. The Na+-K+-ATPase 1-subunit was exclusively localized apically in the human choroid plexus epithelial cells. Immunoreactivity for the Na+-K+-2Cl cotransporter, NKCC1, was likewise confined to the apical plasma membrane domain of the epithelium. The Cl/HCO3 exchanger, AE2, was localized basolaterally, as was the Na+-dependent Cl/HCO3 exchanger, NCBE, and the electroneutral Na+-HCO3 cotransporter, NBCn1. No immunoreactivity was found toward the Na+-dependent acid/base transporters NHE1 or NBCe2. Hence, the human choroid plexus epithelium displays an almost identical distribution pattern of water channels and Na+ transporters as the rat and mouse choroid plexus. This general cross species pattern suggests central roles for these transporters in choroid plexus functions such as cerebrospinal fluid production. immunohistochemistry; metabolism; cerebrospinal fluid secretion 相似文献
2.
Protease-activated receptor regulation of Cl- secretion in Calu-3 cells requires prostaglandin release and CFTR activation 总被引:1,自引:0,他引:1
Palmer ML Lee SY Maniak PJ Carlson D Fahrenkrug SC O'Grady SM 《American journal of physiology. Cell physiology》2006,290(4):C1189-C1198
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
3.
Functional significance of channels and transporters expressed in the inner ear and kidney 总被引:1,自引:0,他引:1
Lang F Vallon V Knipper M Wangemann P 《American journal of physiology. Cell physiology》2007,293(4):C1187-C1208
A number of ion channels and transporters are expressed in both the inner ear and kidney. In the inner ear, K+ cycling and endolymphatic K+, Na+, Ca2+, and pH homeostasis are critical for normal organ function. Ion channels and transporters involved in K+ cycling include K+ channels, Na+-2Cl–-K+ cotransporter, Na+/K+-ATPase, Cl– channels, connexins, and K+/Cl– cotransporters. Furthermore, endolymphatic Na+ and Ca2+ homeostasis depends on Ca2+-ATPase, Ca2+ channels, Na+ channels, and a purinergic receptor channel. Endolymphatic pH homeostasis involves H+-ATPase and Cl–/HCO3– exchangers including pendrin. Defective connexins (GJB2 and GJB6), pendrin (SLC26A4), K+ channels (KCNJ10, KCNQ1, KCNE1, and KCNMA1), Na+-2Cl–-K+ cotransporter (SLC12A2), K+/Cl– cotransporters (KCC3 and KCC4), Cl– channels (BSND and CLCNKA + CLCNKB), and H+-ATPase (ATP6V1B1 and ATPV0A4) cause hearing loss. All these channels and transporters are also expressed in the kidney and support renal tubular transport or signaling. The hearing loss may thus be paralleled by various renal phenotypes including a subtle decrease of proximal Na+-coupled transport (KCNE1/KCNQ1), impaired K+ secretion (KCNMA1), limited HCO3– elimination (SLC26A4), NaCl wasting (BSND and CLCNKB), renal tubular acidosis (ATP6V1B1, ATPV0A4, and KCC4), or impaired urinary concentration (CLCNKA). Thus, defects of channels and transporters expressed in the kidney and inner ear result in simultaneous dysfunctions of these seemingly unrelated organs. cochlea; vestibular labyrinth; stria vascularis; deafness; renal tubule 相似文献
4.
Alvarez LJ Zamudio AC Candia OA 《American journal of physiology. Cell physiology》2005,289(1):C138-C147
Experiments were conducted to determine whether the Cl secretagogue, 1-ethyl-2-benzimidazolinone (EBIO), stimulates Cl transport in the rabbit conjunctival epithelium. For this study, epithelia were isolated in an Ussing-type chamber under short-circuit conditions. The effects of EBIO on the short-circuit current (Isc) and transepithelial resistance (Rt) were measured under physiological conditions, as well as in experiments with altered electrolyte concentrations. Addition of 0.5 mM EBIO to the apical bath stimulated the control Isc by 64% and reduced Rt by 21% (P < 0.05; paired data). Under Cl-free conditions, Isc stimulation using EBIO was markedly attenuated. In the presence of an apical-to-basolateral K+ gradient and permeabilization of the apical membrane, the majority of the Isc reflected the transcellular movement of K+ via basolateral K+ channels. Under these conditions, EBIO in combination with A23187 elicited nearly instantaneous 6090% increases in Isc that were sensitive to the calmodulin antagonist calmidazolium and the K+ channel blocker tetraethyl ammonium. In the presence of an apical-to-basolateral Cl gradient and nystatin permeabilization of the basolateral aspect, EBIO increased the Cl-dependent Isc, an effect prevented by the channel blocker glibenclamide (0.3 mM). The latter compound also was used to determine the proportion of EBIO-evoked unidirectional 36Cl fluxes in the presence of the Cl gradient that traversed the epithelium transcellularly. Overall, EBIO activated apical Cl channels and basolateral K+ channels (presumably those that are Ca2+ dependent), thereby suggesting that this compound, or related derivatives, may be suitable as topical agents to stimulate fluid transport across the tissue in individuals with lacrimal gland deficiencies. Ussing chamber; short-circuit current; electrolyte transport; chloride secretagogue; potassium conductance; 1-ethyl-2-benzimidazolinone; 1,10-phenanthroline 相似文献
5.
Three distinct mechanisms of HCO3- secretion in rat distal colon 总被引:1,自引:0,他引:1
Vidyasagar S Rajendran VM Binder HJ 《American journal of physiology. Cell physiology》2004,287(3):C612-C621
HCO3 secretion has long been recognized in the mammalian colon, but it has not been well characterized. Although most studies of colonic HCO3 secretion have revealed evidence of lumen Cl dependence, suggesting a role for apical membrane Cl/HCO3 exchange, direct examination of HCO3 secretion in isolated crypt from rat distal colon did not identify Cl-dependent HCO3 secretion but did reveal cAMP-induced, Cl-independent HCO3 secretion. Studies were therefore initiated to determine the characteristics of HCO3 secretion in isolated colonic mucosa to identify HCO3 secretion in both surface and crypt cells. HCO3 secretion was measured in rat distal colonic mucosa stripped of muscular and serosal layers by using a pH stat technique. Basal HCO3 secretion (5.6 ± 0.03 µeq·h1·cm2) was abolished by removal of either lumen Cl or bath HCO3; this Cl-dependent HCO3 secretion was also inhibited by 100 µM DIDS (0.5 ± 0.03 µeq·h1·cm2) but not by 5-nitro-3-(3-phenylpropyl-amino)benzoic acid (NPPB), a Cl channel blocker. 8-Bromo-cAMP induced Cl-independent HCO3 secretion (and also inhibited Cl-dependent HCO3 secretion), which was inhibited by NPPB and by glibenclamide, a CFTR blocker, but not by DIDS. Isobutyrate, a poorly metabolized short-chain fatty acid (SCFA), also induced a Cl-independent, DIDS-insensitive, saturable HCO3 secretion that was not inhibited by NPPB. Three distinct HCO3 secretory mechanisms were identified: 1) Cl-dependent secretion associated with apical membrane Cl/HCO3 exchange, 2) cAMP-induced secretion that was a result of an apical membrane anion channel, and 3) SCFA-dependent secretion associated with an apical membrane SCFA/HCO3 exchange. chloride/bicarbonate exchange; short-chain fatty acid/bicarbonate exchange; anion channel; pH stat 相似文献
6.
Foroutan S Brillault J Forbush B O'Donnell ME 《American journal of physiology. Cell physiology》2005,289(6):C1492-C1501
Brain edema that forms during the early stages of stroke involves increased transport of Na+ and Cl across an intact blood-brain barrier (BBB). Our previous studies have shown that a luminal BBB Na+-K+-Cl cotransporter is stimulated by conditions present during ischemia and that inhibition of the cotransporter by intravenous bumetanide greatly reduces edema formation in the rat middle cerebral artery occlusion model of stroke. The present study focused on investigating the effects of hypoxia, which develops rapidly in the brain during ischemia, on the activity and expression of the BBB Na+-K+-Cl cotransporter, as well as on Na+-K+-ATPase activity, cell ATP content, and intracellular volume. Cerebral microvascular endothelial cells (CMECs) were assessed for Na+-K+-Cl cotransporter and Na+-K+-ATPase activities as bumetanide-sensitive and ouabain-sensitive 86Rb influxes, respectively. ATP content was assessed by luciferase assay and intracellular volume by [3H]-3-O-methyl-D-glucose and [14C]-sucrose equilibration. We found that 30-min exposure of CMECs to hypoxia ranging from 7.5% to 0.5% O2 (vs. 19% normoxic O2) significantly increased cotransporter activity as did 7.5% or 2% O2 for up to 2 h. This was not associated with reduction in Na+-K+-ATPase activity or ATP content. CMEC intracellular volume increased only after 4 to 5 h of hypoxia. Furthermore, glucose and pyruvate deprivation increased cotransporter activity under both normoxic and hypoxic conditions. Finally, we found that hypoxia increased phosphorylation but not abundance of the cotransporter protein. These findings support the hypothesis that hypoxia stimulation of the BBB Na+-K+-Cl cotransporter contributes to ischemia-induced brain edema formation. edema; blood-brain barrier; bumetanide; cell volume 相似文献
7.
This paper reports the effects of low O2 concentration (001,0055, and 0.115mol m3) in nutrient solutions onK+/Na+ selectivity of growing and mature root tissues of 6-to 8-d-old, intact, wheat (Triticum aestivum cv. Gamenya) seedlings. Increases in anaerobic catabolism and decreases in O2 uptake,K+ uptake and K+/Na+ selectivity were all more pronounced and/oroccurred at higher external O2 concentrations in the apex (02mm) than in the expanding tissues (24 mm); these growingtissues were, in turn, more affected than the expanded tissuesof the roots (412 mm). Selectivity for K+ over Na+ in roots and shoots was particularlysensitive to O2 deficiency. For example, in apical tissues (02mm) K + /Na+ selectivity was already reduced at 0.115 mol m3O2, yet at this O2 concentration there was no effect on eithergrowth or (K+/Na+) uptake. Upon transfer from 0.01 to 0.26 mol m3 O2, a detailedstudy of the 12 mm root tips showed that 70% of these tips regainedhigh (K+ + Na+) concentrations and K+/Na+ ratios. In contrast,there was no recovery in the remaining 30% of the 12 mm roottips. Net K+ transport to the shoots during the period afterre-aeration was negative for the population as a whole. Theseverity of these effects supports the view that the root tipsand the stele were more susceptible to O2 deficiency than wasthe cortex of the fully-developed root tissues. Key words: Hypoxia, K+/Na+ selectivity, expanded and expanding tissues 相似文献
8.
The relevance of nongenomic pathways to regulation of epithelial function by aldosterone is poorly understood. Recently, we demonstrated that aldosterone inhibits transepithelial HCO3 absorption in the renal medullary thick ascending limb (MTAL) through a nongenomic pathway. Here, we examined the transport mechanism(s) responsible for this regulation, focusing on Na+/H+ exchangers (NHE). In the MTAL, apical NHE3 mediates H+ secretion necessary for HCO3 absorption; basolateral NHE1 influences HCO3 absorption by regulating apical NHE3 activity. In microperfused rat MTALs, the addition of 1 nM aldosterone rapidly decreased HCO3 absorption by 30%. This inhibition was unaffected by three maneuvers that inhibit basolateral Na+/H+ exchange and was preserved in MTALs from NHE1 knockout mice, ruling out the involvement of NHE1. In contrast, exposure to aldosterone for 15 min caused a 30% decrease in apical Na+/H+ exchange activity over the intracellular pH range from 6.5 to 7.7, due to a decrease in Vmax. Inhibition of HCO3 absorption by aldosterone was not affected by 0.1 mM lumen Zn2+ or 1 mM lumen DIDS, arguing against the involvement of an apical H+ conductance or apical K+-HCO3 cotransport. These results demonstrate that aldosterone inhibits HCO3 absorption in the MTAL through inhibition of apical NHE3, and identify NHE3 as a target for nongenomic regulation by aldosterone. Aldosterone may influence a broad range of epithelial transport functions important for extracellular fluid volume and acid-base homeostasis through direct regulation of this exchanger. thick ascending limb; acid-base transport; epithelial Na+ transport; kidney 相似文献
9.
Channel-forming peptide modulates transepithelial electrical conductance and solute permeability 总被引:3,自引:0,他引:3
Broughman JR Brandt RM Hastings C Iwamoto T Tomich JM Schultz BD 《American journal of physiology. Cell physiology》2004,286(6):C1312-C1323
NC-1059, a synthetic channel-forming peptide, transiently increases transepithelial electrical conductance (gTE) and ion transport (as indicated by short-circuit current) across Madin-Darby canine kidney (MDCK) cell monolayers in a time- and concentration-dependent manner when apically exposed. gTE increases from <2 to >40 mS/cm2 over the low to middle micromolar range. Dextran polymer (9.5 but not 77 kDa) permeates the monolayer following apical NC-1059 exposure, suggesting that modulation of the paracellular pathway accounts for changes in gTE. However, concomitant alterations in junctional protein localization (zonula occludens-1, occludin) and cellular morphology are not observed. Effects of NC-1059 on MDCK gTE occur in nominally Cl- and Na+-free apical media, indicating that permeation by these ions is not required for effects on gTE, although two-electrode voltage-clamp assays with Xenopus oocytes suggest that both Cl and Na+ permeate NC-1059 channels with a modest Cl permselectivity (PCl:PNa = 1.3). MDCK monolayers can be exposed to multiple NC-1059 treatments over days to weeks without diminution of response, alteration in the time course, or loss of responsiveness to physiological and pharmacological secretagogues. Together, these results suggest that NC-1059 represents a valuable tool to investigate tight junction regulation and may be a lead compound for therapeutic interventions. transepithelial resistance; cystic fibrosis; tight junction; epithelial barrier; amphipathic -helix 相似文献
10.
K+ channel KVLQT1 located in the basolateral membrane of distal colonic epithelium is not essential for activating Cl- secretion 总被引:1,自引:0,他引:1
Liao T Wang L Halm ST Lu L Fyffe RE Halm DR 《American journal of physiology. Cell physiology》2005,289(3):C564-C575
The cellular mechanism for Cl and K+ secretion in the colonic epithelium requires K+ channels in the basolateral and apical membranes. Colonic mucosa from guinea pig and rat were fixed, sectioned, and then probed with antibodies to the K+ channel proteins KVLQT1 (Kcnq1) and minK-related peptide 2 (MiRP2, Kcne3). Immunofluorescence labeling for Kcnq1 was most prominent in the lateral membrane of crypt cells in rat colon. The guinea pig distal colon had distinct lateral membrane immunoreactivity for Kcnq1 in crypt and surface cells. In addition, Kcne3, an auxiliary subunit for Kcnq1, was detected in the lateral membrane of crypt and surface cells in guinea pig distal colon. Transepithelial short-circuit current (Isc) and transepithelial conductance (Gt) were measured for colonic mucosa during secretory activation by epinephrine (EPI), prostaglandin E2 (PGE2), and carbachol (CCh). HMR1556 (10 µM), an inhibitor of Kcnq1 channels (Gerlach U, Brendel J, Lang HJ, Paulus EF, Weidmann K, Brüggemann A, Busch A, Suessbrich H, Bleich M, and Greger R. J Med Chem 44: 38313837, 2001), partially (50%) inhibited Cl secretory Isc and Gt activated by PGE2 and CCh in rat colon with an IC50 of 55 nM, but in guinea pig distal colon Cl secretory Isc and Gt were unaltered. EPI-activated K+-secretory Isc and Gt also were essentially unaltered by HMR1556 in both rat and guinea pig colon. Although immunofluorescence labeling with a Kcnq1 antibody supported the basolateral membrane presence in colonic epithelium of the guinea pig as well as the rat, the Kcnq1 K+ channel is not an essential component for producing Cl secretion. Other K+ channels present in the basolateral membrane presumably must also contribute directly to the K+ conductance necessary for K+ exit during activation of Cl secretion in the colonic mucosa. HMR1556; K+ secretion; epinephrine; prostaglandin E2; cholinergic 相似文献
11.
Absorptive epithelial cells must admit large quantities of salt (NaCl) during the transport process. How these cells avoid swelling to protect functional integrity in the face of massive salt influx is a fundamental, unresolved problem. A special preparation of the human sweat duct provides critical insights into this crucial issue. We now show that negative feedback control of apical salt influx by regulating the cystic fibrosis transmembrane conductance regulator (CFTR) Cl channel activity is key to this protection. As part of this control process, we report a new physiological role of K+ in intracellular signaling and provide the first direct evidence of acute in vivo regulation of CFTR dephosphorylation activity. We show that cytosolic K+ concentration ([K+]c) declines as a function of increasing cellular NaCl content at the onset of absorptive activity. Declining [K+]c cause parallel deactivation of CFTR by dephosphorylation, thereby limiting apical influx of Cl (and its co-ion Na+) until [K+]c is stabilized. We surmise that [K+]c stabilizes when Na+ influx decreases to a level equal to its efflux through the basolateral Na+-K+ pump thereby preventing disruptive changes in cell volume. electrolytes; phosphatases; protein kinase A; cystic fibrosis transmembrane conductance regulator; epithelial Na+ channel 相似文献
12.
The Ionic Relations of Acetabularia mediterranea 总被引:3,自引:0,他引:3
The concentrations of K+, Na+, and Cl in the cytoplasmand the vacuole of Acetabularia mediterranea have been measured,as have the vacuolar concentrations of SO4 andoxalate. The electrical potential difference between externalsolution, and vacuole and cytoplasm has been measured. The resultsindicate that Cl and SO4 are probably transportedactively into the cell, and that active transport of Na+ isoutwards. The results for K+ are equivocal. The fluxes of K+,Na+, Cl, and S04 into the cell and theeffluxes of Na+ and Cl have been determined. The Clfluxes are extremely large. In all cases the plasmalemma isthe rate-limiting membrane for ion movement. A technique isdescribed for the preparation of large, completely viable cellfragments containing only cytoplasm, with no vacuole. 相似文献
13.
Hydrogen peroxide inhibits cAMP-induced Cl- secretion across colonic epithelial cells 总被引:1,自引:0,他引:1
DuVall Michael D.; Guo Yi; Matalon Sadis 《American journal of physiology. Cell physiology》1998,275(5):C1313
We examined the effects ofH2O2on Cl secretion acrosshuman colonic T84 cells grown on permeable supports and mounted in modified Ussing chambers. Forskolin-induced short-circuit current, ameasure of Cl secretion,was inhibited in a concentration-dependent fashion when monolayers werepretreated withH2O2for 30 min (30-100% inhibition between 500 µM and 5 mM).Moreover,H2O2inhibited 76% of the Clcurrent across monolayers when the basolateral membranes were permeabilized with nystatin (200 µg/ml). When the apical membrane waspermeabilized with amphotericin B,H2O2inhibited the Na+ current (ameasure ofNa+-K+-ATPaseactivity) by 68% but increased theK+ current more than threefold. Inaddition to its effects on ion transport pathways,H2O2also decreased intracellular ATP levels by 43%. We conclude that theprincipal effect ofH2O2on colonic Cl secretion isinhibitory. This may be due to a decrease in ATP levels followingH2O2treatment, which subsequently results in an inhibition of the apicalmembrane Cl conductance andbasolateral membraneNa+-K+-ATPaseactivity. Alternatively,H2O2may alter Cl secretion bydirect action on the transporters or alterations in signal transductionpathways. 相似文献
14.
Distinct K+ conductive pathways are required for Cl- and K+ secretion across distal colonic epithelium 总被引:1,自引:0,他引:1
Secretion of Cl and K+ in the colonic epithelium operates through a cellular mechanism requiring K+ channels in the basolateral and apical membranes. Transepithelial current [short-circuit current (Isc)] and conductance (Gt) were measured for isolated distal colonic mucosa during secretory activation by epinephrine (Epi) or PGE2 and synergistically by PGE2 and carbachol (PGE2 + CCh). TRAM-34 at 0.5 µM, an inhibitor of KCa3.1 (IK, Kcnn4) K+ channels (H. Wulff, M. J. Miller, W. Hänsel, S. Grissmer, M. D. Cahalan, and K. G. Chandy. Proc Natl Acad Sci USA 97: 81518156, 2000), did not alter secretory Isc or Gt in guinea pig or rat colon. The presence of KCa3.1 in the mucosa was confirmed by immunoblot and immunofluorescence detection. At 100 µM, TRAM-34 inhibited Isc and Gt activated by Epi (4%), PGE2 (30%) and PGE2 + CCh (60%). The IC50 of 4.0 µM implicated involvement of K+ channels other than KCa3.1. The secretory responses augmented by the K+ channel opener 1-EBIO were inhibited only at a high concentration of TRAM-34, suggesting further that KCa3.1 was not involved. Sensitivity of the synergistic response (PGE2 + CCh) to a high concentration TRAM-34 supported a requirement for multiple K+ conductive pathways in secretion. Clofilium (100 µM), a quaternary ammonium, inhibited Cl secretory Isc and Gt activated by PGE2 (20%) but not K+ secretion activated by Epi. Thus Cl secretion activated by physiological secretagogues occurred without apparent activity of KCa3.1 channels but was dependent on other types of K+ channels sensitive to high concentrations of TRAM-34 and/or clofilium. epinephrine; prostaglandin E2; cholinergic; Kcnn4; TRAM-34; clofilium 相似文献
15.
Osmotic and Ionic Regulation in Chara L-cell Fragments 总被引:1,自引:0,他引:1
Ion absorption from rather complicated artificial pond water(APW) by cell fragments having a lower osmotic pressure thanthe intact internodal cell (L-cell fragments) was studied. L-cellfragments were prepared by taking advantage of trans cellularosmosis and ligating the cell with thread. The results wereas follows: (1) L-cell fragments absorbed more K+ than Na+ fromaKCL + NaCl mixture in the presence of Ca2+, Mg2+ and SO24 inthe light; (2) the influx of KCI was larger than that of KNO3;(3) the amount of positive charge carried by K+, Na+ and Mg2+across the cell membrane balanced well with the amount of negativecharge carried by Cl in Cl-containing and NO3-free APW; (4) no conclusion could be made as to whether ornot the rule of electro neutrality held for the K+, Na+, Ca2+and NO3 fluxes across the cell membrane, because dilutedKNO3 is unstable; (5) L-cell fragments in KCl-containing APWsurvived longer than those in KNO3-containing and Cl-free APW; (6) after incubation in KNO3-containing and Cl-freeAPW, L-cell fragments absorbed a great amount of KCI immediatelyafter being transferred to KCl-containing and NO3 -freeAPW; and (7) lowering the turgor pressure of the intact cellby raising the external osmotic pressure did not induce ionflux into the cell. Thus, we concluded that the L-cell fragmentsabsorbed ions from the external solution not because of theirlower turgor pressure, but because of the diluted ion concentrationof the cytoplasm and the vacuole. The electroneutrality ruleheld, at least, for K+, Na+, Mg2+ and Cl influxes acrossthe cell membrane inthe KCl-containing and NO3-free APW.These results were analyzed on the basis of an extended poremodel which presumed the existence of ATP-dependent processesin the membrane, and suggested that K+, Na+ and Mg2+ inflowsinto an L-cell fragment are likely to be induced by active Clinflow. (Received May 18, 1987; Accepted September 29, 1987) 相似文献
16.
Possible reasons for relative salt stress tolerance in nodules of white lupin cv. Multolupa 总被引:5,自引:2,他引:3
Fernndez-Pascual M.; de Lorenzo C.; de Felipe M.R.; Rajalakshmi S.; Gordon A.J.; Thomas B.J.; Minchin F.R. 《Journal of experimental botany》1996,47(11):1709-1716
The effects of different NaCl concentrations on the growth andnitrogen fixation activity of white lupin (Lupinus albus [L.])was studied over a 6 d period. Plant growth parameters, photosynthesisand shoot respiration were unaffected by NaCl concentrationsup to 150 mol m3. However, nitrogenase activity decreasedwith increased NaCl concentration up to 100 mol m3, whilstthe O2 diffusion resistance increased with 100 mol m3NaCl, but showed no further change when 150 mol m3 NaClwas applied for 6 d. Increases in NaCl concentration decreasednodular starch content while increasing sucrose content, suggestingan osmotic regulation. These changes were associated with a77% decrease in sucrose synthase activity. The effect on theO2 diffusion resistance was paralleled by changes in glycoproteincontent of the nodules, as determined by immunogold localizationand ELISA. X-ray microanalysis studies of nodules showed that,following a 6 d exposure to 150 mol m3 NaCl, Na+ ionswere largely excluded from the infected zone, whilst only lowlevels of Cl- ions penetrated into this region. Na+ entry intoroots and leaves was also at a low level. Leghaemoglobin contentdecreased with saline stress, as did superoxide dismutase; whichdecreased by 36% following exposure to 100 mol m3 saltfor 6 d. These results are discussed in relation to the relativesalt tolerance of the Multolupa/ISLU-16 symbiosis. Key words: Salt stress, nodules, nitrogen fixation, oxygen diffusion, carbohydrates, Lupinus albus 相似文献
17.
Involvement of anion channel(s) in the modulation of the transient outward K(+) channel in rat ventricular myocytes 总被引:5,自引:0,他引:5
Lai XG Yang J Zhou SS Zhu J Li GR Wong TM 《American journal of physiology. Cell physiology》2004,287(1):C163-C170
The cardiac Ca2+-independent transient outward K+ current (Ito), a major repolarizing ionic current, is markedly affected by Cl substitution and anion channel blockers. We reexplored the mechanism of the action of anions on Ito by using whole cell patch-clamp in single isolated rat cardiac ventricular myocytes. The transient outward current was sensitive to blockade by 4-aminopyridine (4-AP) and was abolished by Cs+ substitution for intracellular K+. Replacement of most of the extracellular Cl with less permeant anions, aspartate (Asp) and glutamate (Glu), markedly suppressed the current. Removal of external Na+ or stabilization of F-actin with phalloidin did not significantly affect the inhibitory action of less permeant anions on Ito. In contrast, the permeant Cl substitute Br did not markedly affect the current, whereas F substitution for Cl induced a slight inhibition. The Ito elicited during Br substitution for Cl was also sensitive to blockade by 4-AP. The ability of Cl substitutes to induce rightward shifts of the steady-state inactivation curve of Ito was in the following sequence: NO3 > Cl Br > gluconate > Glu > Asp. Depolymerization of actin filaments with cytochalasin D (CytD) induced an effect on the steady-state inactivation of Ito similar to that of less permeant anions. Fluorescent phalloidin staining experiments revealed that CytD-pretreatment significantly decreased the intensity of FITC-phalloidin staining of F-actin, whereas Asp substitution for Cl was without significant effect on the intensity. These results suggest that the Ito channel is modulated by anion channel(s), in which the actin cytoskeleton may be implicated. transient outward potassium current; anion channel; actin cytoskeleton; myocyte; potassium ion 相似文献
18.
MURALITHARAN MORLEY S.; CHANDLER STEPHEN F.; VAN STEVENINCK REINHARD F. M. 《Annals of botany》1992,69(5):459-465
Non-selected and Na2SO-, K2SO4- or KCl-selected callus culturesof Vaccinium corymbosum L. cv. Blue Crop were grown on mediasupplemented with 0, 25 and 50 mM Na2SO4 (non-selected and Na2SO(-selectedonly), 0, 25 and 50mMK2SO4 (non-selected and K2SO4-selectedonly) or 0, 50 and 100 mM KCl (non-selected and KCl-selectedonly). On all media, growth of selected callus (on a fresh-weightor dry-weight basis) was greater than that of non-selected callus,and selected callus grew optimally on the level and type ofsalt on which it was selected. Selected callus was friable andmaintained a higher f. wt:d. wt ratio. Tissue water potentialin selected callus was more negative than in non-selected callus. Flame photometry and chloridometry showed Na+, K+ and Claccumulated in callus to concentrations equal to or greaterthan the initial concentration in the medium. Turbidometry showedthat tissue SO42- concentration was lower than the concentrationin the medium. In most cases selected callus accumulated moreNa+, Ksup, SO42 or Cl than non-selected callus.Vacuolar ion concentration was measured by electronprobe X-raymicroanalysis, and on most media selected callus had highervacuolar ion concentrations than non-selected callus. SO42and Cl were accumulated in the vacuoles at concentrationshigher than the external medium, but vacuolar Na+ concentrationdid not reach external concentration on Na2SO4 and on potassiumsalts was maintained between 12 and 17 mM. Vacuolar K+ concentration(approx. 142191 mM on no salt) decreased on Na2SO4 andincreased on K2SO4 and KCl. There was no precise correlation between total or specific ionaccumulation (Na+, K+, SO42 and Cl and fresh-weightyield. Results suggest that selection results in adaptationin response to decreased water potential of the medium. Vaccinium corymbosum, blueberry, electronprobe X-ray microanalysis, callus, in vitro selection, salt tolerance, KCl, K2SO4, Na2SO4 相似文献
19.
Ion Composition of the Chara Internode 总被引:2,自引:0,他引:2
Ion compositions of the cytoplasm and the vacuole of Chara australiswere analyzed according to Kishimoto and Tazawa (1964) and Kiyosawa(1979a). The ions in the cytoplasm and the vacuole analyzedwere K+, Na+, Ca2+, Mg2+, Cl, NO3 and H2PO4.Assuming that the volume of the cytoplasm Vp is 10% of thatof the whole cell V, the concentrations of K+, Na+, Ca2+, Mg2+,Cl, NO3 and H2PO4 in the cytoplasm averaged70, 15, 13, 4.6, 31, 2.2 and 16 mM, respectively. If the volumeof the cytoplasm was assumed to be 5% of that of the whole cell,their averaged concentrations were 139, 31, 25, 9.2, 62, 4.4and 33 mM, respectively. The averaged ion compositions of thecell sap were K+, 111; Na+, 47; Ca2+, 4.4; Mg2+, 8.9; Cl,91; NO3, 3.3 and H2PO4, 6.0 mM. These values,taking the concentrations and the charges of the protein (Kiyosawa1979b) and amino acids (Sakano and Tazawa 1984) into accountand assuming the presence of some uni- or oligovalent anionsand/or small nonelectrolyte molecules, could explain fairlywell both the electroneutrality and the osmotic pressure ofthe cell, except when Vp/V = 5%. (Received May 18, 1987; Accepted September 29, 1987) 相似文献
20.
Plants of Lupinus albus L., cv. Ultra, were grown hydroponicallywith NO3-nutrition for 51 d under control (0.05 mol m3Na+ and 10 mol m3 Cl) and saline (40 mol m3NaCI) conditions. Plants were harvested 41 and 51 d after germinationand analysed for content and net increment of C, N and the mineralcations K+, Na+, Mg2+, and Ca2+ and the anions Cl, NOJ,malate, phosphate, and SO42. Roots, stem interaodes,petioles and leaflets were analysed separately. During the studyperiod net photosynthesis, respiratory losses of CO2 from shootand root and the composition of the spontaneously bleeding phloemsap and the root pressure xylem exudate were also determined.Using molar ratios of C over N in the transport fluids, incrementsof C and N, and photosynthetic gains as well as respiratorylosses of C, the net flows of C and N in the xylem and phloemwere then calculated as in earlier studies (Pate, Layzell andMcNeill, 1979a). Knowing the carbon flows, the ratios of ionto carbon in the phloem sap, and ion increments in individualorgans, net flows of K+, Na+, and Cl over the study periodwere also calculated. Salt stress led to a general decrease of all partial componentsof C and N partitioning indicating that inhibitions were notdue to specific effects of NaCI salinity on photosynthesis oron NO3 uptake. However, there were differences between variouslyaged organs, and net phloem export of nitrogenous compoundsfrom ageing leaves was substantially enhanced under saline conditions.In addition, NO3reduction in the roots was specificallyinhibited. Uptake and xylem transport of K+ was more severelyinhibited than photosynthetic carbon gain or NO3 uptakeby the root. K+ transport in the phloem was even more severelyrestricted under saline conditions. Na+ and Cl flowsand uptake, on the other hand, were substantially increasedin the presence of salt and, in particular, there were thenmassive flows of Na in the phloem. The results are discussedin relation to the causes of salt sensitivity of Lupinus albus.The data suggest that both a restriction of K+ supply and astrongly increased phloem translocation of Na+ contribute tothe adverse effects of salt in this species. Restriction ofK+ supply occurs by diminished K+ uptake and even more by reducedK+ cycling within the plant. Key words: Lupinus albus, salt stress, phloem transport, xylem transport, partitioning, carbon, nitrogen, K+, Na+, CI 相似文献