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1.
Bouzinova EV Praetorius J Virkki LV Nielsen S Boron WF Aalkjaer C 《American journal of physiology. Cell physiology》2005,289(6):C1448-C1456
Several studies suggest the involvement of Na+ and HCO3 transport in the formation of cerebrospinal fluid. Two Na+-dependent HCO3 transporters were recently localized to the epithelial cells of the rat choroid plexus (NBCn1 and NCBE), and the mRNA for a third protein was also detected (NBCe2) (Praetorius J, Nejsum LN, and Nielsen S. Am J Physiol Cell Physiol 286: C601C610, 2004). Our goal was to immunolocalize the NBCe2 to the choroid plexus by immunohistochemistry and immunogold electronmicroscopy and to functionally characterize the bicarbonate transport in the isolated rat choroid plexus by measurements of intracellular pH (pHi) using a dual-excitation wavelength pH-sensitive dye (BCECF). Both antisera derived from COOH-terminal and NH2-terminal NBCe2 peptides localized NBCe2 to the brush-border membrane domain of choroid plexus epithelial cells. Steady-state pHi in choroidal cells increased from 7.03 ± 0.02 to 7.38 ± 0.02 (n = 41) after addition of CO2/HCO3 into the bath solution. This increase was Na+ dependent and inhibited by the Cl and HCO3 transport inhibitor DIDS (200 µM). This suggests the presence of Na+-dependent, partially DIDS-sensitive HCO3 uptake. The pHi recovery after acid loading revealed an initial Na+ and HCO3-dependent net base flux of 0.828 ± 0.116 mM/s (n = 8). The initial flux in the presence of CO2/HCO3 was unaffected by DIDS. Our data support the existence of both DIDS-sensitive and -insensitive Na+- and HCO3-dependent base loader uptake into the rat choroid plexus epithelial cells. This is consistent with the localization of the three base transporters NBCn1, Na+-driven Cl bicarbonate exchanger, and NBCe2 in this tissue. bicarbonate metabolism; BCECF; cerebrospinal fluid; acid/base transport; ammonium prepulse 相似文献
2.
Functional demonstration of Na+-K+-2Cl- cotransporter activity in isolated, polarized choroid plexus cells 总被引:1,自引:0,他引:1
Wu Qiang; Delpire Eric; Hebert Steven C.; Strange Kevin 《American journal of physiology. Cell physiology》1998,275(6):C1565
The function of the apicalNa+-K+-2Clcotransporter in mammalian choroid plexus (CP) is uncertain andcontroversial. To investigate cotransporter function, we developed anovel dissociated rat CP cell preparation in which single, isolatedcells maintain normal polarized morphology. Immunofluorescencedemonstrated that in isolated cells theNa+-K+-ATPase,Na+-K+-2Clcotransporter, and aquaporin 1 water channel remained localized to thebrush border, whereas theCl/HCO3(anion) exchanger type 2 was confined to the basolateral membrane. Weutilized video-enhanced microscopy and cell volume measurementtechniques to investigate cotransporter function. Application of 100 µM bumetanide caused CP cells to shrink rapidly. Elevation ofextracellular K+ from 3 to 6 or 25 mM caused CP cells to swell 18 and 33%, respectively. Swelling wasblocked completely by Na+ removalor by addition of 100 µM bumetanide. Exposure of CP cells to 5 mMBaCl2 induced rapid swelling thatwas inhibited by 100 µM bumetanide. We conclude that the CPcotransporter is constitutively active and propose that it functions inseries with Ba2+-sensitiveK+ channels to reabsorbK+ from cerebrospinal fluid to blood. 相似文献
3.
Banizs B Komlosi P Bevensee MO Schwiebert EM Bell PD Yoder BK 《American journal of physiology. Cell physiology》2007,292(4):C1409-C1416
Tg737orpk mice have defects in cilia assembly and develop hydrocephalus in the perinatal period of life. Hydrocephalus is progressive and is thought to be initiated by abnormal ion and water transport across the choroid plexus epithelium. The pathology is further aggravated by the slow and disorganized beating of motile cilia on ependymal cells that contribute to decreased cerebrospinal fluid movement through the ventricles. Previously, we demonstrated that the hydrocephalus phenotype is associated with a marked increase in intracellular cAMP levels in choroid plexus epithelium, which is known to have regulatory effects on ion and fluid movement in many secretory epithelia. To evaluate whether the hydrocephalus in Tg737orpk mutants is associated with defects in ion transport, we compared the steady-state pHi and Na+-dependent transport activities of isolated choroid plexus epithelium tissue from Tg737orpk mutant and wild-type mice. The data indicate that Tg737orpk mutant choroid plexus epithelium have lower pHi and higher Na+-dependent HCO3 transport activity compared with wild-type choroid plexus epithelium. In addition, wild-type choroid plexus epithelium could be converted to a mutant phenotype with regard to the activity of Na+-dependent HCO3 transport by addition of dibutyryl-cAMP and mutant choroid plexus epithelium toward the wild-type phenotype by inhibiting PKA activity with H-89. Together, these data suggest that cilia have an important role in regulating normal physiology of choroid plexus epithelium and that ciliary dysfunction in Tg737orpk mutants disrupts a signaling pathway leading to elevated intracellular cAMP levels and aberrant regulation of pHi and ion transport activity. cAMP; ion transport 相似文献
4.
Nejsum LN Praetorius J Nielsen S 《American journal of physiology. Cell physiology》2005,289(2):C333-C340
In isolated sweat glands, bumetanide inhibits sweat secretion. The mRNA encoding bumetanide-sensitive Na+-K+-Cl cotransporter (NKCC) isoform 1 (NKCC1) has been detected in sweat glands; however, the cellular and subcellular protein localization is unknown. Na+/H+ exchanger (NHE) isoform 1 (NHE1) protein has been localized to both the duct and secretory coil of human sweat duct; however, the NHE1 abundance in the duct was not compared with that in the secretory coil. The aim of this study was to test whether mRNA encoding NKCC1, NKCC2, and Na+-coupled acid-base transporters and the corresponding proteins are expressed in rodent sweat glands and, if expressed, to determine the cellular and subcellular localization in rat, mouse, and human eccrine sweat glands. NKCC1 mRNA was demonstrated in rat palmar tissue, including sweat glands, using RT-PCR, whereas NKCC2 mRNA was absent. Also, NHE1 mRNA was demonstrated in rat palmar tissue, whereas NHE2, NHE3, NHE4, electrogenic Na+-HCO3 cotransporter 1 NBCe1, NBCe2, electroneutral Na+-HCO3 cotransporter NBCn1, and Na+-dependent Cl/HCO3 exchanger NCBE mRNA were not detected. The expression of NKCC1 and NHE1 proteins was confirmed in rat palmar skin by immunoblotting, whereas NKCC2, NHE2, and NHE3 proteins were not detected. Immunohistochemistry was performed using sections from rat, mouse, and human palmar tissue. Immunoperoxidase labeling revealed abundant expression of NKCC1 and NHE1 in the basolateral domain of secretory coils of rat, mouse, and human sweat glands and low expression was found in the coiled part of the ducts. In contrast, NKCC1 and NHE1 labeling was absent from rat, mouse, and human epidermis. Immunoelectron microscopy demonstrated abundant NKCC1 and NHE1 labeling of the basolateral plasma membrane of mouse sweat glands, with no labeling of the apical plasma membranes or intracellular structures. The basolateral NKCC1 of the secretory coils of sweat glands would most likely account for the observed bumetanide-sensitive NaCl secretion in the secretory coils, and the basolateral NHE1 is likely to be involved in Na+-coupled acid-base transport. bumetanide; eccrine glands; immunohistochemistry; immunoblotting 相似文献
5.
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
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.
Role of NBC1 in apical and basolateral HCO3- permeabilities and transendothelial HCO3- fluxes in bovine corneal endothelium 总被引:1,自引:0,他引:1
Corneal transparency and hydration control are dependent on HCO3 transport properties of the corneal endothelium. Recent work (13) suggested the presence of an apical 1Na+-3HCO3 cotransporter (NBC1) in addition to a basolateral 1Na+-2HCO3 cotransporter. We examined whether the NBC1 cotransporter contributes significantly to basolateral or apical HCO3 permeability and whether the cotransporter participates in transendothelial net HCO3 flux in cultured bovine corneal endothelium. NBC1 protein expression was reduced using small interfering RNA (siRNA). Immunoblot analysis showed that 515 nM siRNA decreased NBC1 expression by 8095%, 4 days posttransfection. Apical and basolateral HCO3 permeabilities were determined by measuring the rate of pHi change when HCO3 was removed from the bath under constant pH or constant CO2 conditions. Using either protocol, we found that cultures treated with NBC1 siRNA had sixfold lower basolateral HCO3 permeability than untreated or siCONTROL siRNA-treated cells. Apical HCO3 permeability was unaffected by NBC1 siRNA treatment. Net non-steady-state HCO3 flux was 0.707 ± 0.009 mM·min1·cm2 in the basolateral-to-apical direction and increased to 1.74 ± 0.15 when cells were stimulated with 2 µM forskolin. Treatment with 5 nM siRNA decreased basolateral-to-apical flux by 67%, whereas apical-to-basolateral flux was unaffected, significantly decreasing net HCO3 flux to 0.236 ± 0.002. NBC1 siRNA treatment or 100 µM ouabain also eliminated steady-state HCO3 flux, as measured by apical compartment alkalinization. Collectively, reduced basolateral HCO3 permeability, basolateral-to-apical fluxes, and net HCO3 flux as a result of reduced expression of NBC1 indicate that NBC1 plays a key role in transendothelial HCO3 flux and is functional only at the basolateral membrane. corneal endothelium; sodium bicarbonate cotransporter; small interfering RNA; bicarbonate transport 相似文献
8.
Cowley EA Sellers MC Illsley NP 《American journal of physiology. Cell physiology》2005,288(4):C891-C898
Resting or basal intracellular pH (pHi) measured in cultured human syncytiotrophoblast cells was 7.26 ± 0.04 (without HCO3) or 7.24 ± 0.03 (with HCO3). Ion substitution and inhibitor experiments were performed to determine whether common H+-transporting species were operating to maintain basal pHi. Removal of extracellular Na+ or Cl or addition of amiloride or dihydro-4,4'-diisothiocyanatostilbene-2,2'-disulfonate (H2DIDS) had no effect. Acidification with the K+/H+ exchanger nigericin reduced pHi to 6.25 ± 0.15 (without HCO3) or 6.53 ± 0.10 (with HCO3). In the presence of extracellular Na+, recovery to basal pHi was prompt and occurred at similar rates in the absence and presence of HCO3. Ion substitution and inhibition experiments were also used to identify the species mediating the return to basal pHi after acidification. Recovery was inhibited by removal of Na+ or addition of amiloride, whereas removal of Cl and addition of H2DIDS were ineffective. Addition of the Na+/H+ exchanger monensin to cells that had returned to basal pHi elicited a further increase in pHi to 7.48 ± 0.07. Analysis of recovery data showed that there was a progressive decrease in pH per minute as pHi approached the basal level, despite the continued presence of a driving force for H+ extrusion. These data show that in cultured syncytial cells, in the absence of perturbation, basal pHi is preserved despite the absence of active, mediated pH maintenance. They also demonstrate that an Na+/H+ antiporter acts to defend the cells against acidification and that it is the sole transporter necessary for recovery from an intracellular acid load. sodium/hydrogen antiporter; pH regulation; fluorescence; 2',7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein 相似文献
9.
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
10.
Gagnon KB England R Delpire E 《American journal of physiology. Cell physiology》2006,290(1):C134-C142
In the present study, we have demonstrated functional interaction between Ste20-related proline-alanine-rich kinase (SPAK), WNK4 [with no lysine (K)], and the widely expressed Na+-K+-2Cl cotransporter type 1 (NKCC1). NKCC1 function, which we measured in Xenopus laevis oocytes under both isosmotic (basal) and hyperosmotic (stimulated) conditions, was unaffected when SPAK and WNK4 were expressed alone. In contrast, expression of both kinases with NKCC1 resulted in a significant increase in cotransporter activity and an insensitivity to external osmolarity or cell volume. NKCC1 activation is dependent on the catalytic activity of SPAK and likely also of WNK4, because mutations in their catalytic domains result in an absence of cotransporter stimulation. The results of our yeast two-hybrid experiments suggest that WNK4 does not interact directly with NKCC1 but does interact with SPAK. Functional experiments demonstrated that the binding of SPAK to WNK4 was also required because a SPAK-interaction-deficient WNK4 mutant (Phe997Ala) did not increase NKCC1 activity. We also have shown that the transport function of K+-Cl cotransporter type 2 (KCC2), a neuron-specific KCl cotransporter, was diminished by the expression of both kinases under both isosmotic and hyposmotic conditions. Our data are consistent with WNK4 interacting with SPAK, which in turn phosphorylates and activates NKCC1 and phosphorylates and deactivates KCC2. bumetanide; Na+-K+-2Cl cotransporter; K+-Cl cotransporter; Xenopus oocytes 相似文献
11.
Na+ influx and Na+-K+ pump activation during short-term exposure of cardiac myocytes to aldosterone 总被引:1,自引:0,他引:1
Mihailidou Anastasia S.; Buhagiar Kerrie A.; Rasmussen Helge H. 《American journal of physiology. Cell physiology》1998,274(1):C175
To examine the effect of aldosterone on sarcolemmalNa+ transport, we measuredouabain-sensitive electrogenicNa+-K+pump current(Ip) involtage-clamped ventricular myocytes and intracellularNa+ activity(aiNa) in right ventricularpapillary muscles. Aldosterone (10 nM) induced an increase in bothIp and the rateof rise of aiNa duringNa+-K+pump blockade with the fast-acting cardiac steroid dihydroouabain. Thealdosterone-induced increase inIp and rate ofrise of aiNa was eliminated bybumetanide, suggesting that aldosterone activates Na+ influx through theNa+-K+-2Clcotransporter. To obtain independent support for this, theNa+,K+, andCl concentrations in thesuperfusate and solution of pipettes used to voltage clamp myocyteswere set at levels designed to abolish the inward electrochemicaldriving force for theNa+-K+-2Clcotransporter. This eliminated the aldosterone-induced increase inIp. We concludethat in vitro exposure of cardiac myocytes to aldosterone activates theNa+-K+-2Clcotransporter to enhance Na+influx and stimulate theNa+-K+pump. 相似文献
12.
Substance P inhibits bicarbonate secretion from guinea pig pancreatic ducts by modulating an anion exchanger 总被引:2,自引:0,他引:2
The stimulatory pathways controlling HCO3- secretion by the pancreatic ductal epithelium are well described. However, only a few data are available concerning inhibitory mechanisms, which may play an important role in the physiological control of the pancreas. The aim of this study was to investigate the cellular mechanism by which substance P (SP) inhibits pancreatic ductal HCO3- secretion. Small intra/interlobular ducts were isolated from the pancreas of guinea pigs. During overnight culture the ducts seal to form a closed sac. Transmembrane HCO3- fluxes were calculated from changes in intracellular pH (measured using the pH-sensitive dye BCECF) and the buffering capacity of the cells. We found that secretin can stimulate HCO3- secretion in guinea pig pancreatic ducts about fivefold and that this effect could be totally blocked by SP. The inhibitory effect of SP was relieved by spantide, an SP receptor antagonist. SP had no effect on the activity of basolateral Na+-HCO3- cotransporters and Na+/H+ exchangers. However, the peptide did inhibit a Cl--dependent HCO3- efflux (secretory) mechanism, most probably the Cl-/HCO3 exchanger on the apical membrane of the duct cell. pancreas; Cl-/HCO3- exchanger; tachykinin 相似文献
13.
Salinity-induced Malate Accumulation in Chara 总被引:3,自引:0,他引:3
Ion absorption by Chara corallina from solutions containingpredominantly KC1 or RbCl at up to 100 mol m3 resultedin accumulation of salts and turgor regulation. Turgor regulationdid not occur in solutions containing Na+ or Li+salts. Duringion absorption from various salts of K+ and Rb+ vacuolar cationconcentration exceeded Cl concentration. This differencewas shown to be balanced by the synthesis and accumulation ofmalate. Vacuolar malate concentration reached 48 mol m3,with accumulation occurring at rates of up to 0.45 mol m3h1. Malate accumulation was inhibited by low externalpH and was dependent upon external HCO3 concentration.The synthesis of malic acid and its subsequent dissociationimposed a severe acid load on the cell. Biophysical regulationof cellular pH was achieved by a H+efflux at a rate of about40 nmol m2 s1from the cell. The results presentedargue against cytoplasmic Cl, HCO3 or pH regulatingmalate accumulation in Chara and it is suggested that malatetransport across the tonoplast may regulate malate accumulation. Key words: Malate, Chara corallina, pH regulation, salinity 相似文献
14.
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
15.
Millhouse, J. and Strother, S. 1987. Further characteristicsof salt-dependent bicarbonate use by the seagrass Zostera muelleri.J.exp. Bot. 38: 10551068. The contribution of HCO3to photosynthetic O2 evolutionin the seagrass Zostera muelleri Irmisch ex Aschers. increasedwith increasing salinity of the bathing seawater when the inorganiccarbon concentration was kept constant. K1/2 (seawater salts)for HCO3 -dependent photosynthesis was 66% of seawatersalinity. Both short- and long-term pretreatment at low salinitiesstimulated photosynthesis in full strength seawater. Twentyfour hours pre-incubation of seagrass plants in 3·0 molm3 NaHCO3 resulted in increased photosynthesis at allsalinities, apparently due to stimulation of HCO3 use(K1/2 (seawater salts) = 26%). Vmax (HCO3) was not affectedby low salinity pretreatment. The kinetics of HCO3 stimulationby the major seawater cations was investigated. Ca2+ was themost effective cation with the highest Vmax (HCO3) andwith K1/2(Ca2+) = 14 mol m3. Mg2+ was also very effectiveat less than 50 mol m3 but higher concentrations wereinhibitory. This inhibition cannot be accounted for solely byprecipitation of MgCO3. Na+ and K+ were both capable of stimulatingHCO3 use. Stimulation was in two distinct parts. Up to500 mol m3, both citrate and chloride salts gave similarresults (K1/2(Na+) 81 mol m3, Vmax(HCO3) 0·26µmol O2 mg1 chl min1), but use of citratesalts above 500 mol m2 caused a second stimulation ofHCO3 use (K1/2(Na+) 830 mol m3, Vmax(HCO3)0·68 µmol O2 mg1 chl min1). Vmax(HCO3)for the second-phase Na+ or K+ stimulation was of the same orderas for Ca2+-stimulated HCO3 use. To further characterizesalt-dependent HCO3 use, the sensitivity of photosynthesisto Tris and TES buffers was investigated. The effects of Trisappear to be due to the action of Tris+ causing stimulationof HCO3 -dependent photosynthesis in the absence of salt,but inhibition of HCO3 use in saline media. TES has noeffect on photosynthesis. External carbonic anhydrase, althoughimplicated in salt-dependent HCO3 use in Z. muelleri,could not be detected in whole leaves. Key words: Zostera muelleri, HCO3 use, salinity 相似文献
16.
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
17.
The effect of changes in ambient oxygen concentration on the bioelectric properties of middle ear mucosa 总被引:2,自引:0,他引:2
Mandell DL Devor DC Madia JV Lo CY Hake H Hebda PA 《American journal of physiology. Cell physiology》2003,285(3):C618-C622
The purpose of the present study was to compare the effect of 24 h of exposure to 7% O2 (normal middle ear physiological conditions) vs. 21% O2 (found in the middle ear after ventilation tube placement) on transepithelial Na+ absorption and Cl secretion in cultured gerbil middle ear epithelial cell monolayers. Although no difference in apical Na+ absorption was identified, the UTP-induced stimulation of apical Cl secretion in the presence of apical Na+ channel blockade with amiloride was significantly enhanced after exposure to 21% O2 compared with 7% O2 exposure. In the presence of a calcium-activated Cl channel inhibitor, DIDS, UTP-induced stimulation of Cl secretion after 21% O2 exposure was decreased, suggesting a role for calcium-activated Cl channels in middle ear Cl secretion in response to relative hyperoxia. ion channels; sodium; chloride; hypoxia 相似文献
18.
Hirono C Nakamoto T Sugita M Iwasa Y Akagawa Y Shiba Y 《The Journal of membrane biology》2001,180(1):11-19
Forskolin-induced anion currents and depolarization were investigated to clarify the mechanism of HCO3
− secretion in the intralobular duct cells of rat parotid glands. Anion currents of the cells were measured at the equilibrium
potential of K+, using a gramicidin-perforated patch technique that negligibly affects intracellular anion concentration. The forskolin-induced
anion current was sustained and significantly (54%) suppressed by glibenclamide (200 μm), a blocker of the cystic fibrosis transmembrane conductance regulator (CFTR) Cl− channel. The anion current was markedly suppressed by addition of 1 mm methazolamide, a carbonic anhydrase inhibitor, and removal of external HCO3
−. Forskolin depolarized the cells in the current-clamp mode. Addition of methazolamide and removal of external HCO3
− significantly decreased the depolarizing level. These results suggest that activation of anion channels (mainly the CFTR
Cl− channel located in luminal membranes) and production of cytosolic HCO3
− induce the inward anion current and resulting depolarization. Inhibition of the Na+-K+-2Cl− cotransporter and the Cl−-HCO3
− exchanger had no significant effect on the current or depolarization, indicating that the uptake of Cl− via the Na+-K+-2Cl− cotransporter or the Cl−-HCO3
− exchanger is not involved in the responses. Taken together, we conclude that forskolin activates the outward movement (probably
secretion) of HCO3
− produced intracellularly, but not of Cl− due to lack of active Cl− transport in parotid duct cells, and that the gramicidin-perforated patch method is very useful to analyze anion transport.
Received: 17 June 2000/Revised: 14 November 2000 相似文献
19.
Carlin RW Sedlacek RL Quesnell RR Pierucci-Alves F Grieger DM Schultz BD 《American journal of physiology. Cell physiology》2006,290(6):C1560-C1571
Epithelial ion transport disorders, including cystic fibrosis, adversely affect male reproductive function by nonobstructive mechanisms and by obstruction of the distal duct. Continuous cell lines that could be used to define ion transport mechanisms in this tissue are not readily available. In the present study, porcine vas deferens epithelial cells were isolated by standard techniques, and the cells spontaneously immortalized to form a porcine vas deferens epithelial cell line that we have titled PVD9902. Cells were maintained in continuous culture for >4 yr and 200 passages in a typical growth medium. Frozen stocks were generated, and thawed cells exhibited growth characteristics indistinguishable from their nonfrozen counterparts. Molecular and immunocytochemical studies confirmed the origin and epithelial nature of these cells. When seeded on permeable supports, PVD9902 cells grew as electrically tight (>6,000 ·cm2), confluent monolayers that responded to forskolin with an increase in short-circuit current (Isc; 8 ± 1 µA/cm2) that required Cl, HCO3, and Na+, and was partially sensitive to bumetanide. mRNA was expressed for a number of anion transporters, including CFTR, electrogenic Na+-HCO3 cotransporter 1b (NBCe1b), downregulated in adenoma, pendrin, and Cl/formate exchanger. Both forskolin and isoproterenol caused an increase in cellular cAMP levels. In addition, PVD9902 cell monolayers responded to physiological (i.e., adenosine, norepinephrine) and pharmacological [i.e., 5'-(N-ethylcarboxamido)adenosine, isoproterenol] agonists with increases in Isc. Unlike their freshly isolated counterparts, however, PVD9902 cells did not respond to glucocorticoid exposure with an increase in amiloride-sensitive Isc. RT-PCR analysis revealed the presence of both glucocorticoid and mineralocorticoid receptor mRNA as well as mRNA for the - and -subunits of the epithelia Na+ channels (- and -ENaC), but not -ENaC. Nonetheless, PVD9902 cells recapitulated most observations in freshly isolated cells and thus represent a powerful new tool to characterize mechanisms that contribute to male reproductive function. male reproductive tract; cystic fibrosis; epithelial Na+ channel expression; glucocorticoid receptor; adrenergic; vasopressin 相似文献
20.
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