共查询到20条相似文献,搜索用时 15 毫秒
1.
Raquel L. Bernardino Ana D. Martins Sílvia Socorro Marco G. Alves Pedro F. Oliveira 《The Journal of membrane biology》2013,246(12):877-883
The formation of competent spermatozoa is a complex event that depends on the establishment of adequate environments throughout the male reproductive tract. This includes the control of bicarbonate (HCO3 ?) concentration, which plays an essential role in the maintenance of extracellular and intracellular pH (pHi) values. Diabetes mellitus alters pHi regulation in mammalian cells, mainly by altering the activity of ion transporters, particularly HCO3 ?-dependent mechanisms. Yet, little is known about the effects of this pathology and its prodromal stage, prediabetes, on the membrane transport mechanisms of male reproductive tract cells. Herein, we analyzed protein and mRNA levels of the most relevant HCO3 ? transporters of the SLC4 family [anion exchanger 2 (AE2), Na+-driven Cl?/HCO3 ? exchanger (NDCBE), electrogenic Na+/HCO3 ? cotransporter 1 (NBCe1), electroneutral Na+/HCO3 ? cotransporter 1 (NBCn1)] in the testis and epididymis of a prediabetic animal model. Firstly, we identified the HCO3 ? transporters of the SLC4 family, in both testicular and epididymal tissue. Secondly, although no alterations were detected in protein expression, mRNA levels of NBCe1, NBCn1 and NDCBE were significantly increased in the testis of prediabetic rats. On the other hand, in the epididymis, prediabetes caused an increase of AE2 and a decrease of NDCBE protein levels. These alterations may be translated into changes of HCO3 ? transepithelial epididymal fluxes in vivo, which may represent a threat for sperm survival. Moreover, these results provide evidence of the molecular mechanism that may be responsible for the significant increase in abnormal sperm morphology already reported in prediabetic rats. 相似文献
2.
Zinnia N. Noor Joachim W. Deitmer Shefeeq M. Theparambil 《Journal of cellular physiology》2019,234(1):89-99
Sodium plays a major role in different astrocytic functions, including maintenance of ion homeostasis and uptake of neurotransmitters and metabolites, which are mediated by different Na+-coupled transporters. In the current study, the role of an electrogenic sodium-bicarbonate cotransporter (NBCe1), a sodium-potassium-chloride transporter 1 (NKCC1) and sodium-potassium ATPase (Na+-K+-ATPase) for the maintenance of [Na+]i was investigated in cultured astrocytes of wild-type (WT) and of NBCe1-deficient (NBCe1-KO) mice using the Na+-sensitive dye, asante sodium green-2. Our results suggest that cytosolic Na+ was higher in the presence of CO2/HCO3− (15 mM) than CO2/HCO3−-free, HEPES-buffered solution in WT, but not in NBCe1-KO astrocytes (12 mM). Surprisingly, there was a strong dependence of cytosolic [Na+] on the extracellular [HCO3−] attributable to NBCe1 activity. Pharmacological blockage of NKCC1 with bumetanide led to a robust drop in cytosolic Na+ in both WT and NBCe1-KO astrocytes by up to 6 mM. There was a strong dependence of the cytosolic [Na+] on the extracellular [K+]. Inhibition of the Na+-K+-ATPase led to larger increase in cytosolic Na+, both in the absence of K+ as compared with the presence of ouabain and in NBCe1-KO astrocytes as compared with WT astrocytes. Our results show that cytosolic Na+ in mouse cortical astrocytes can vary considerably and depends greatly on the concentrations of HCO3− and K+, attributable to the activity of the Na+-K+-ATPase, of NBCe1 and NKCC1. 相似文献
3.
HCO3
− translocation across the plasma membrane via the electrogenic Na/HCO3
− cotransporter NBCe1 plays an important role in intracellular pH regulation and transepithelial HCO3
− transport. However, the structural determinants of transporter function remain largely unknown. A previous study showed that
the putative fourth extracellular loop (EL4) plays an essential role in determining the electrogenicity of NBCe1. In the present
study, we generated eight new chimeras of human NBCe1-A and NBCn1-A. All possess the putative NBCe1 EL4 and are electrogenic.
Chimera O, in which the putative sixth transmembrane segment (TM6) and EL5 through the C terminus (Ct) of NBCe1 was replaced
by corresponding NBCn1 sequence, produces the smallest hyperpolarization (1–2 mV) when CO2/HCO3
− is added to the extracellular solution. Biotinylation experiments show that O has a very low abundance at the plasma membrane.
However, chimeras in which we simultaneously replaced the putative TM6 and smaller subdomains of the EL5-Ct region for the
NBCn1 sequence were strongly electrogenic except for chimera T, in which we replaced TM6 and TM12 of NBCe1 with the corresponding
regions of NBCn1. T exhibited greatly reduced transporter surface expression compared to wild-type NBCe1-A, while retaining
at least some electrogenic character. We hypothesize that putative TM6 and TM12 are part of a functional unit and that if
the two TMs are replaced by those of the same transporter type, high surface expression would require that the surrounding
TMs are also from the same transporter type. 相似文献
4.
Inyeong Choi Hansoo Yang Eunjin Kim Soojung Lee 《Current issues in molecular biology》2022,44(3):1284
The sodium bicarbonate cotransporter NBCn1 is an electroneutral transporter with a channel activity that conducts Na+ in a HCO3–-independent manner. This channel activity was suggested to functionally affect other membrane proteins which permeate Na+ influx. We previously reported that NBCn1 is associated with the NMDA receptors (NMDARs) at the molecular and physiological levels. In this study, we examined whether NBCn1 channel activity affects NMDAR currents and whether this effect involves the interaction between the two proteins. NBCn1 and the NMDAR subunits GluN1A/GluN2A were expressed in Xenopus oocytes, and glutamate currents produced by the receptors were measured using two-electrode voltage clamp. In the absence of CO2/HCO3–, NBCn1 channel activity decreased glutamate currents mediated by GluN1A/GluN2A. NBCn1 also decreased the slope of the current–voltage relationships for the glutamate current. Similar effects on the glutamate current were observed with and without PSD95, which can cluster NBCn1 and NMDARs. The channel activity was also observed in the presence of CO2/HCO3–. We conclude that NBCn1 channel activity decreases NMDAR function. Given that NBCn1 knockout mice develop a downregulation of NMDARs, our results are unexpected and suggest that NBCn1 has dual effects on NMDARs. It stabilizes NMDAR expression but decreases receptor function by its Na+ channel activity. The dual effects may play an important role in fine-tuning the regulation of NMDARs in the brain. 相似文献
5.
Andreas A. Danielsen Mark D. Parker Soojung Lee Walter F. Boron Christian Aalkjaer Ebbe Boedtkjer 《The Journal of biological chemistry》2013,288(12):8146-8155
Activation of Na+,HCO3− cotransport in vascular smooth muscle cells (VSMCs) contributes to intracellular pH (pHi) control during artery contraction, but the signaling pathways involved have been unknown. We investigated whether physical and functional interactions between the Na+,HCO3− cotransporter NBCn1 (slc4a7) and the Ca2+/calmodulin-activated serine/threonine phosphatase calcineurin exist and play a role for pHi control in VSMCs. Using a yeast two-hybrid screen, we found that splice cassette II from the N terminus of NBCn1 interacts with calcineurin Aβ. When cassette II was truncated or mutated to disrupt the putative calcineurin binding motif PTVVIH, the interaction was abolished. Native NBCn1 and calcineurin Aβ co-immunoprecipitated from A7r5 rat VSMCs. A peptide (acetyl-DDIPTVVIH-amide), which mimics the putative calcineurin binding motif, inhibited the co-immunoprecipitation whereas a mutated peptide (acetyl-DDIATAVAA-amide) did not. Na+,HCO3− cotransport activity was investigated in VSMCs of mesenteric arteries after an NH4+ prepulse. During depolarization with 50 mm extracellular K+ to raise intracellular [Ca2+], Na+,HCO3− cotransport activity was inhibited 20–30% by calcineurin inhibitors (FK506 and cyclosporine A). FK506 did not affect Na+,HCO3− cotransport activity in VSMCs when cytosolic [Ca2+] was lowered by buffering, nor did it disrupt binding between NBCn1 and calcineurin Aβ. FK506 augmented the intracellular acidification of VSMCs during norepinephrine-induced artery contractions. No physical or functional interactions between calcineurin Aβ and the Na+/H+ exchanger NHE1 were observed in VSMCs. In conclusion, we demonstrate a physical interaction between calcineurin Aβ and cassette II of NBCn1. Intracellular Ca2+ activates Na+,HCO3− cotransport activity in VSMCs in a calcineurin-dependent manner which is important for protection against intracellular acidification. 相似文献
6.
Eun Namkoong Yong-Hwan Shin Jun-Seok Bae Seulki Choi Minkyoung Kim Nahyun Kim Sung-Min Hwang Kyungpyo Park 《PloS one》2015,10(9)
Sodium bicarbonate cotransporters (NBCs) are involved in the pH regulation of salivary glands. However, the roles and regulatory mechanisms among different NBC isotypes have not been rigorously evaluated. We investigated the roles of two different types of NBCs, electroneutral (NBCn1) and electrogenic NBC (NBCe1), with respect to pH regulation and regulatory mechanisms using human submandibular glands (hSMGs) and HSG cells. Intracellular pH (pHi) was measured and the pHi recovery rate from cell acidification induced by an NH4Cl pulse was recorded. Subcellular localization and protein phosphorylation were determined using immunohistochemistry and co-immunoprecipitation techniques. We determined that NBCn1 is expressed on the basolateral side of acinar cells and the apical side of duct cells, while NBCe1 is exclusively expressed on the apical membrane of duct cells. The pHi recovery rate in hSMG acinar cells, which only express NBCn1, was not affected by pre-incubation with 5 μM PP2, an Src tyrosine kinase inhibitor. However, in HSG cells, which express both NBCe1 and NBCn1, the pHi recovery rate was inhibited by PP2. The apparent difference in regulatory mechanisms for NBCn1 and NBCe1 was evaluated by artificial overexpression of NBCn1 or NBCe1 in HSG cells, which revealed that the pHi recovery rate was only inhibited by PP2 in cells overexpressing NBCe1. Furthermore, only NBCe1 was significantly phosphorylated and translocated by NH4Cl, which was inhibited by PP2. Our results suggest that both NBCn1 and NBCe1 play a role in pHi regulation in hSMG acinar cells, and also that Src kinase does not regulate the activity of NBCn1. 相似文献
7.
Yi-Lin Zhang Jian-Chang Feng Li-Jiao Ke Jia-Wen Xu Ze-Xin Huang Jiehong Huang Yun-Xin Zhu Wen-Liang Zhou 《Journal of cellular physiology》2019,234(9):15790-15799
The vagina provides a characteristic low-Na+ and low-pH fluid microenvironment that is considered generally protective. Previous studies have shown that various types of epithelial cells harbor the capacity of intracellular pH (pHi) regulation. However, it remains elusive whether vaginal epithelium could actively regulate pHi by transporting acid–base ions. In this study, we verified that after transient exposure to NH4Cl, the pHi values could rapidly recover from acidification via Na+-H+ exchanger (NHE), Na+-HCO3− cotransporter (NBC), and carbonic anhydrase in human vaginal epithelial cell line VK2/E6E7. Positive expression of the main acid–base transporters including NHE1-2, NBCe1-2, and NBCn1 mRNA was also detected in VK2/E6E7 cells. Moreover, the in vivo study further showed that interfering with the function of V-type H+-ATPase, NHE or NBC expressed in vagina impaired vaginal luminal pH homeostasis in rats. Taken together, our study reveals the property of pH regulation in vaginal epithelial cells, which might provide novel insights into the potential role of vaginal epithelium in the formation of the vaginal acidic microenvironment. 相似文献
8.
Although AHCYL2 (long-IRBIT) is highly homologous to IRBIT, which regulates ion-transporting proteins including the electrogenic Na+-HCO3− cotransporter NBCe1-B, its functions are poorly understood. Here, we found that AHCYL2 interacts with NBCe1-B in bovine parotid acinar cells using yeast two-hybrid, immunofluorescence confocal microscopy and co-immunoprecipitation analyses. Whole-cell patch-clamp experiments revealed that co-expression of AHCYL2 reduces the apparent affinity for intracellular Mg2+ in inhibition of NBCe1-B currents specifically in a HCO3−-deficient cellular condition. Our data unveil AHCYL2 as a potential regulator of NBCe1-B in mammalian cells. We propose that cytosolic ionic condition appropriate for AHCYL2 to function might be different from IRBIT. 相似文献
9.
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
10.
Han Soo Yang Eunjin Kim Soojung Lee Hae Jeong Park Deborah S. Cooper Ira Rajbhandari Inyeong Choi 《The Journal of biological chemistry》2009,284(23):15970-15979
To understand the mechanism for ion transport through the sodium/bicarbonate transporter SLC4A4 (NBCe1), we examined amino acid residues, within transmembrane domains, that are conserved among electrogenic Na/HCO3 transporters but are substituted with residues at the corresponding site of all electroneutral Na/HCO3 transporters. Point mutants were constructed and expressed in Xenopus oocytes to assess function using two-electrode voltage clamp. Among the mutants, D555E (charge-conserved substitution of the aspartate at position 555 with a glutamate) produced decreasing HCO3− currents at more positive membrane voltages. Immunohistochemistry showed D555E protein expression in oocyte membranes. D555E induced Na/HCO3-dependent pH recovery from a CO2-induced acidification. Current-voltage relationships revealed that D555E produced an outwardly rectifying current in the nominally CO2/HCO3−-free solution that was abolished by Cl− removal from the bath. In the presence of CO2/HCO3−, however, the outward current produced by D555E decreased only slightly after Cl− removal. Starting from a Cl−-free condition, D555E produced dose-dependent outward currents in response to a series of chloride additions. The D555E-mediated chloride current decreased by 70% in the presence of CO2/HCO3−. The substitution of Asp555 with an asparagine also produced a Cl− current. Anion selectivity experiments revealed that D555E was broadly permissive to other anions including NO3−. Fluorescence measurements of chloride transport were done with human embryonic kidney HEK 293 cells expressing NBCe1 and D555E. A marked increase in chloride transport was detected in cells expressing D555E. We conclude that Asp555 plays a role in HCO3− selectivity.The electrogenic Na/HCO3 cotransporter NBCe1 (SLC4A4) is one of the SLC4A gene family members transporting HCO3− across the plasma membrane (1–3). NBCe1 plays a role in transepithelial HCO3− movement and pHi regulation in many tissues (4–6). NBCe1 is responsible for HCO3− reabsorption in the proximal tubules of the kidney (7). The proximal tubule cells reclaim HCO3− from the lumen through a series of reactions involving titration of HCO3− by H+ secretion via the apical Na/H exchanger, production of CO2, and regeneration of HCO3− and H+ in the tubule cells. HCO3− then moves to the interstitium via the basolateral NBCe1. The essential feature driving this basolateral Na+/HCO3− exit is the stoichiometry of 1:3 Na+:HCO3−, which makes the equilibrium potential for NBCe1 more positive than the resting membrane potential of the proximal tubule cells (8). The stoichiometry of 1Na+:1HCO3− or 1Na+:2HCO3− causes both ions to move into cells in other tissues such as pancreas, brain, and cardiovascular tissues (9, 10).Despite the importance of NBCe1 for basolateral HCO3− reabsorption in the proximal tubules, the mechanism of electrogenic Na/HCO3 transport via the transporter is not well understood. Ion movement depends on loading ions at their translocation or binding sites that likely reside within the membrane field at some distance from the bath solution (11). This implies that the transmembrane domains (TMs)2 of NBCe1 and amino acid residues within TMs play critical roles in ion transport.Sequence analysis of different SLC4A proteins shows similar hydropathy plots, predicting that these proteins share structural elements of transport function (12). Such similarities have facilitated structure/function studies to define molecular domains or motifs responsible for conferring Na/HCO3 transport of NBCe1. Abuladze et al. (13) performed a large scale mutagenesis on acidic and basic amino acids in non-TMs and found many residues affecting Na+-dependent base flux. McAlear et al. (14) identified amino acids in TM8 involving ion translocation. By a systematic approach of chimeric transporters between NBCe1 and the electroneutral Na/HCO3 cotransporter NBCn1 (SLC4A7) (15), we and our colleagues (16) demonstrated that electrogenic Na/HCO3 transport of NBCe1 requires interactions between the regions TM1–5 and TM6–13 of the protein. Zhu et al. (17) recently proposed TM1 as a domain lining the ion translocation pathway. On the other hand, Chang et al. (18) reported that the cytoplasmic N-terminal domain might contribute to HCO3− permeation.In the present study, we searched amino acid residues that are highly conserved among electrogenic Na/HCO3 transporters but not among electroneutral Na/HCO3 transporters and examined their role in electrogenic Na/HCO3 transport. Nine candidate residues in human renal NBCe1-A (5, 19) were selected and mutated by replacement with the amino acids at the corresponding sites of NBCn1. Mutant transporters were expressed in Xenopus oocytes and assessed via two-electrode voltage clamp. Our data show that Asp555 of NBCe1 plays an important role in HCO3− selectivity. 相似文献
11.
The sodium bicarbonate cotransporter (NBC1) is essential for bicarbonate transport across plasma membranes in epithelial
and nonepithelial cells. The direction of the NaHCO3 movement in secretory epithelia is opposite to that in reabsorptive epithelia. In secretory epithelia (such as pancreatic
duct cells) NBC is responsible for the transport of bicarbonate from blood to the cell for eventual secretion at the apical
membrane. In reabsorptive epithelia (such as kidney proximal tubule cells) NBC is responsible for the reabsorption of bicarbonate
from cell to the blood. In nonepithelial cells this transporter is mainly involved with cell pH regulation. Recent molecular
cloning experiments have identified the existence of four NBC isoforms (NBC1, 2, 3 and 4) and two NBC-related proteins AE4
and NCBE (Anion Exchanger 4 and Na-dependent Chloride-Bicarbonate Exchanger). All but AE4 are presumed to mediate the cotransport
of Na+ and HCO3
− under normal conditions and may be functionally altered in certain pathologic states. NBC1 shows a limited tissue expression
pattern, is electrogenic and plays an important role in bicarbonate reabsorption in kidney proximal tubule. In addition to
the kidney, NBC1 is expressed in pancreatic duct cells, is activated by cystic fibrosis transmembrane conductance regulator
(CFTR) and plays an important role in HCO3
− secretion. NBC2 and NBC3 have a wider tissue distribution than NBC1, are electroneutral, and are involved with cell pH regulation.
The characterization of NBC4 is incomplete. The NBC-related protein called NCBE mediates Na-dependent, Cl−/Bicarbonate Exchange. The purpose of this review is to summarize recent advances on the cloning of NBC isoforms and related
proteins and their role and regulation in physiologic and pathologic states.
Received: 26 February 2001/Revised: 14 May 2001 相似文献
12.
13.
Mette Flinck Signe Hoejland Kramer Julie Schnipper Anne Poder Andersen 《Cell cycle (Georgetown, Tex.)》2018,17(9):1056-1067
Precise acid-base homeostasis is essential for maintaining normal cell proliferation and growth. Conversely, dysregulated acid-base homeostasis, with increased acid extrusion and marked extracellular acidification, is an enabling feature of solid tumors, yet the mechanisms through which intra- and extracellular pH (pHi, pHe) impact proliferation and growth are incompletely understood. The aim of this study was to determine the impact of pH, and specifically of the Na+/H+ exchanger NHE1 and Na+, HCO3? transporter NBCn1, on cell cycle progression and its regulators in human breast cancer cells. Reduction of pHe to 6.5, a common condition in tumors, significantly delayed cell cycle progression in MCF-7 human breast cancer cells. The NHE1 protein level peaked in S phase and that of NBCn1 in G2/M. Steady state pHi changed through the cell cycle, from 7.1 in early S phase to 6.8 in G2, recovering again in M phase. This pattern, as well as net acid extrusion capacity, was dependent on NHE1 and NBCn1. Accordingly, knockdown of either NHE1 or NBCn1 reduced proliferation, prolonged cell cycle progression in a manner involving S phase prolongation and delayed G2/M transition, and altered the expression pattern and phosphorylation of cell cycle regulatory proteins. Our work demonstrates, for the first time, that both NHE1 and NBCn1 regulate cell cycle progression in breast cancer cells, and we propose that this involves cell cycle phase-specific pHi regulation by the two transporters. 相似文献
14.
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
15.
G. Lauritzen 《Experimental cell research》2010,316(15):2538-1031
Altered pH-regulatory ion transport is characteristic of many cancers; however, the mechanisms and consequences are poorly understood. Here, we investigate how a truncated, constitutively active ErbB2 receptor (ΔNErbB2) common in breast cancer impacts on the Na+/H+-exchanger NHE1 and the Na+,HCO3−-cotransporter NBCn1 in MCF-7 human breast cancer cells and address the roles of these transporters in chemotherapy resistance. Upon ΔNErbB2 expression, mRNA and protein levels of NBCn1, yet not of NHE1, increased several-fold, and the localization of both transporters was altered paralleling extensive morphological changes. The rate of pHi recovery after acid loading increased by 50% upon ΔNErbB2 expression. Knockdown and pharmacological inhibition confirmed the involvement of both NHE1 and NBCn1 in acid extrusion. NHE1 inhibition or knockdown sensitized ΔNErbB2-expressing cells to cisplatin-induced programmed cell death (PCD) in a caspase-, cathepsin-, and reactive oxygen species-dependent manner. NHE1 inhibition augmented cisplatin-induced caspase activity and lysosomal membrane permeability followed by cysteine cathepsin release. In contrast, NBCn1 inhibition attenuated cathepsin release and had no net effect on viability. These findings warrant studies of NHE1 as a potential target in breast cancer and demonstrate that in spite of their similar transport functions, NHE1 and NBCn1 serve different functions in MCF-7 cells. 相似文献
16.
17.
Evidence for Na-Independent HCO(3) Uptake by the Cyanobacterium Synechococcus leopoliensis 总被引:10,自引:10,他引:0
下载免费PDF全文
![点击此处可从《Plant physiology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
At low levels of dissolved inorganic carbon (DIC) and alkaline pH the rate of photosynthesis by air-grown cells of Synechococcus leopoliensis (UTEX 625) was enhanced 7- to 10-fold by 20 millimolar Na+. The rate of photosynthesis greatly exceeded the CO2 supply rate and indicated that HCO3− was taken up by a Na+-dependent mechanism. In contrast, photosynthesis by Synechococcus grown in standing culture proceeded rapidly in the absence of Na+ and exceeded the CO2 supply rate by 8 to 45 times. The apparent photosynthetic affinity (K½) for DIC was high (6-40 micromolar) and was not markedly affected by Na+ concentration, whereas with air-grown cells K½ (DIC) decreased by more than an order of magnitude in the presence of Na+. Lithium, which inhibited Na+-dependent HCO3− uptake in air-grown cells, had little effect on Na+-independent HCO3− uptake by standing culture cells. A component of total HCO3− uptake in standing culture cells was also Na+-dependent with a K½ (Na+) of 4.8 millimolar and was inhibited by lithium. Analysis of 14C-fixation during isotopic disequilibrium indicated that standing culture cells also possessed a Na+-independent CO2 transport system. The conversion from Na+-independent to Na+-dependent HCO3− uptake was readily accomplished by transferring cells grown in standing to growth in cultures bubbled with air. These results demonstrated that the conditions experienced during growth influenced the mode by which Ssynechococcus acquired HCO3− for subsequent photosynthetic fixation. 相似文献
18.
The effect of changing [K+], [Na+] and [Cl?] in nutrient solution was studied in bullfrog antrum with and without HCO3? in nutrient. In 25 mM HCO3? (95% O2/5% CO2) and in zero HCO3? (100% O2), nutrient pH was maintained at 7.3. Changing from 4 to 40 mM K+ or from 81 to 8.1 mM Cl? gave a decrease 10 min later in transmucosal PD (nutrient became more negative) — a normal response. These responses were less in zero than in 25 mM HCO3?. A decrease from 102 to 8 mM Na+ decreased PD (anomalous response of electrogenic NaCl symport). This effect was attenuated or eliminated in zero HCO3?. In contrast, change from 4 to 40 mM K+ gave initial anomalous PD response and change from 102 to 8 mM Na+, initial normal PD response with either zero or 25 mM HCO3?. Both responses were associated with (Na+ + K+)-ATPase pump and were greater in zero than in 25 mM HCO3?. Initial PD increases in zero HCO3? are explained as due to increase in the resistance of passive conductance and/or NaCl symport pathways. Thus, removal of HCO3? modifies conductance pathways of nutrient membrane. 相似文献
19.
20.
NBCe1 (SLC4A4) a potential pH regulator in enamel organ cells during enamel development in the mouse
R. Jalali J. Guo B. Zandieh-Doulabi T. J. M. Bervoets M. L. Paine W. F. Boron M. D. Parker M. J. C. Bijvelds J. F. Medina P. K. DenBesten A. L. J. J. Bronckers 《Cell and tissue research》2014,358(2):433-442