Identification and cloning of the Na/HCO3− cotransporter (NBC) in human corneal endothelium

Sun, Xing; Bonanno, Joseph A.

doi:10.1016/s0014-4835(03)00150-7

Cited by 22 publications

(23 citation statements)

References 29 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…These findings suggested the occurrence of a solute-coupled fluid absorption from the pleural space, consistent with the involvement of a Na + /H + -Cl − /HCO 3 − co-exchanger located on the serosal side of the pleural mesothelium [21,22]. So far, several sodium-dependent HCO 3 − transport isoforms have been cloned [51,52]. The molecular basis of this coupled exchanger activity in pleural tissues requires follow-up studies.…”

mentioning

confidence: 52%

Electrolyte and Fluid Transport in Mesothelial Cells

Ji¹,

Nie²

2008

JEBP

View full text Add to dashboard Cite

Mesothelial cells are specialized epithelial cells, which line the pleural, pericardial, and peritoneal cavities. Accumulating evidence suggests that the monolayer of mesothelial cells is permeable to electrolyte and fluid, and thereby govern both fluid secretion and re-absorption in the serosal cavities. Disorders in these salt and fluid transport systems may be fundamental in the pathogenesis of pleural effusion, pericardial effusion, and ascites. In this review, we discuss the location, physiological function, and regulation of active transport (Na + -K + -ATPase) systems, cation and anion channels (Na + , K + , Cl − , and Ca 2+ channels), antiport (exchangers) systems, and symport (co-transporters) systems, and water channels (aquaporins). These secretive and absorptive pathways across mesothelial monolayer cells for electrolytes and fluid may provide pivotal therapeutical targets for novel clinical intervention in edematous diseases of serous cavities. Keywords mesothelioma; ion channel; permeability; effusion; filtration; ENaC Mesothelial cells are specialized epithelial cells that line the serous cavities, including the pleural, pericardial, and peritoneal cavities in addition to internal organs [1]. While the mesothelium was first described more than a century ago, one of its critical essential functions, namely, its active roles in transerosal transport, in particular, cavity fluid secretion and reabsorption, was long overlooked. Only in last two decades compelling evidence accumulated that mesothelial cells actively transport electrolytes and fluid and, in turn, regulate liquid volume within the cavities. The mesothelium, on the basis of recent increasing experimental evidence, both in vitro and in vivo, is less permeable to electrolytes than was previously assumed, with ion permeability characteristics similar to those in epithelia [2,3]. Herein this article we will review the expression and biophysical features of salt and fluid transport systems, both active and passive, that have been identified in mesothelial cells (Fig. 1, Tables 1 and 2). I. ION CHANNELS AND ATPASE I-1. Amiloride-Inhibitable Cation ChannelsThe epithelial sodium channel (ENaC), as a major pathway which participates in sodium movement across the apical membrane of polarized epithelial cells, has been cloned and characterized [4][5][6] ENaC subunits have been cloned to date, namely α-, β-, γ-, δ-, and ε-ENaC [7]. The biophysical properties of various ENaC channels depend on their subunit compositions. When expressed in oocytes one of "conductive" subunits (α, δ, and ε-ENaC) can form a channel sharing identical biophysical properties to three-subunit channels composed of both a "conductive" subunit and two "non-conductive" subunits, namely, β-and γ-ENaCs. When α-, β-, and γ-ENaC subunits are assembled together, the result is a 4-to 6-pS channel that is highly selective for Na + over K + . In contrast, two-subunit α β-and α γ-ENaC channels display diverse amiloride sensitivity, conductance, and Na + permeability [8]. ENaC is...

show abstract

mentioning

confidence: 52%

Electrolyte and Fluid Transport in Mesothelial Cells

Ji¹,

Nie²

2008

JEBP

View full text Add to dashboard Cite

show abstract

“…This secretion is currently hypothesized to be the source of the ion-coupled osmotic fluid pumping. Uptake of at the basolateral membrane is by co-transport via NBC1b (Li et al, 2005;Sun and Bonanno, 2003;Sun et al, 2000). Apical permeability however, is 3-4 times smaller than basolateral (Bonanno et al, 1999).…”

Section: Discussionmentioning

confidence: 99%

“…Cl − -free Ringer's was used to increase the sensitivity of the assay because Cl − can compete with for anion channels and Cl − -free Ringer's removes any contribution from the weak apical anion exchanger (Bonanno et al, 1999;Zhang et al, 2002). Considering that the amplitude of pH i changes during LB pulses may be influenced by basolateral transporters such as NBC (Bonanno et al, 1999;Sun and Bonanno, 2003), we used only the initial rate of pH i change (dpH i /dt) instead of the amplitude as the criteria for comparison of permeability across the apical membrane in the presence or absence of applied agents. Therefore, the apical permeability will be pre-dominantly contributed by anion channels.…”

Section: Effects Of Bclca1-sirna On Apical Permeability In Cultured Bcecmentioning

confidence: 99%

Molecular expression and functional involvement of the bovine calcium-activated chloride channel 1 (bCLCA1) in apical HCO3− permeability of bovine corneal endothelium

Zhang

Xie

et al. 2006

Experimental Eye Research

View full text Add to dashboard Cite

Corneal endothelium secretes from basolateral (stroma) to apical (anterior chamber) compartments. Apical permeability can be enhanced by increasing [Ca 2+ ] i . We hypothesized that the bovine calcium-activated chloride channel 1 (bCLCA1), shown previously by PCR screening to be expressed in corneal endothelium, is involved in Ca 2+ activated apical permeability. bCLCA1 expression in cultured bovine corneal endothelial cells (CBCEC) was examined by in situ hybridization analysis, immunoblotting, immunofluorescence and confocal microscopy. Rabbit polyclonal antibodies were generated using a 14 aa polypeptide (417-430) from the predicted sequence of bCLCA1. The small interference RNA (siRNA) knock down technique was used to evaluate the functional involvement of bCLCA1 in apical permeability. In situ hybridization confirmed prominent bCLCA1-specific mRNA expression in CBCEC. bCLCA1 antiserum detected the heterologously expressed bCLCA1 in HEK293 cells and a 90 kDa band in CBCEC, which was absent when using the pre-immune serum or antigen absorption of serum. Immunofluoresence staining with anti-bCLCA1 antibody and confocal microscopy indicates an apical membrane location in CBCEC. In CBCEC transfected with bCLCA1 specific siRNA, bCLCA1 expression was reduced by 80%, while transfection with siControl scrambled sequence had no effect. Increasing [ ] by application of ATPγS or cyclopiazonic acid (CPA) increased apical permeability in siControl transfected CBCEC, while having no effect on apical permeability in bCLCA1 specific siRNA transfected cells. Baseline permeability, however, was not different between controls and siRNA treated cells. We conclude that the calcium-activated chloride channel (bCLCA1) is expressed in bovine corneal endothelial cells and can contribute to Ca 2+ dependent apical permeability, but not resting permeability, across the corneal endothelium.

show abstract

“…HCO 3 -uptake at the basolateral (stromal) membrane has been identified as being predominantly via the 1Na + :2HCO 3 -cotransporter (NBCe1) (Sun et al 2000;Sun and Bonanno 2003). A recent study showed that siRNA knockdown of NBC significantly reduced basolateral HCO 3 -permeability and eliminated net basolateral to apical fluxes (Li et al 2005).…”

Section: Introductionmentioning

confidence: 99%

“…The endothelium develops a small apical side negative transendothelial potential (0.5 mV) that is significantly reduced by HCO 3 -withdrawal or by carbonic anhydrase inhibitors (Fischbarg 1972;Barfort and Maurice 1974;Fischbarg and Lim 1974;Hodson et al 1977). Corneal swelling is also induced by the Na + /K + ATPase inhibitor ouabain, indicating that the endothelial pump involves active transport.HCO 3 -uptake at the basolateral (stromal) membrane has been identified as being predominantly via the 1Na + :2HCO 3 -cotransporter (NBCe1) (Sun et al 2000;Sun and Bonanno 2003). A recent study showed that siRNA knockdown of NBC significantly reduced basolateral HCO 3 -permeability and eliminated net basolateral to apical fluxes (Li et al 2005).…”

mentioning

confidence: 99%

Dependence of cAMP meditated increases in Cl− and HCO3− permeability on CFTR in bovine corneal endothelial cells

Allen

Sun

et al. 2008

Experimental Eye Research

Self Cite

View full text Add to dashboard Cite

The Cystic Fibrosis Transmembrane conductance Regulator (CFTR) is present on the apical membrane of corneal endothelial cells. Increasing intracellular [cAMP] with forskolin stimulates an NPPB and glibenclamide-inhibitable apical Cl -and HCO 3 -permeability. To definitively determine that the increased permeability is dependent on CFTR, we used an siRNA knockdown approach. Apical Cl -and HCO 3 -permeability and steady-state HCO 3 -flux were measured in the presence or absence of forskolin using cultured bovine corneal endothelial cells that were transfected with CFTR siRNA or a scrambled sequence control. CFTR protein expression was reduced by ∼80% in CFTR siRNA treated cultures. Forskolin (10 μM) increased apical chloride permeability by 7 fold, which was reduced to control level in siRNA treated cells. CFTR siRNA treatment had no effect on baseline apical chloride permeability. Apical HCO 3 -permeability was increased 2 fold by 10 μM forskolin, which was reduced to control level in siRNA treated cultures. Similarly, there was no effect on baseline apical HCO 3 -permeability by knocking down CFTR expression. The steady-state apicalbasolateral pH gradient (ΔpH) at four hours in control cultures was increased ∼2.5 fold by forskolin. In CFTR siRNA treated cells, the baseline ΔpH was similar to control, however forskolin did not have a significant effect. We conclude that forskolin induced increases in apical HCO 3 -permeability in bovine corneal endothelium requires CFTR. However, CFTR does not have a major role in determining baseline apical chloride or HCO 3 -permeability.The corneal endothelium is responsible for maintaining the hydration and transparency of the cornea by counteracting the fluid imbibition properties of the glycosaminoglycan rich stroma. Numerous studies have shown that this process is dependent on the presence of HCO 3 -and slowed by inhibition of carbonic anhydrase activity (Hodson 1971;Barfort and Maurice 1974;Fischbarg and Lim 1974;Hodson 1974;Kuang et al. 1990;Riley et al. 1995). The endothelium develops a small apical side negative transendothelial potential (0.5 mV) that is significantly reduced by HCO 3 -withdrawal or by carbonic anhydrase inhibitors (Fischbarg 1972;Barfort and Maurice 1974;Fischbarg and Lim 1974;Hodson et al. 1977). Corneal swelling is also induced by the Na + /K + ATPase inhibitor ouabain, indicating that the endothelial pump involves active transport.HCO 3 -uptake at the basolateral (stromal) membrane has been identified as being predominantly via the 1Na + :2HCO 3 -cotransporter (NBCe1) (Sun et al. 2000;Sun and Bonanno 2003). A recent study showed that siRNA knockdown of NBC significantly reduced basolateral HCO 3 -permeability and eliminated net basolateral to apical fluxes (Li et al. 2005). Interestingly, studies using cultured cells indicate that basolateral HCO 3 -permeability is 3-4 times greater than apical permeability (Bonanno et al. 1999). The low HCO 3 -permeability of the apical membrane suggests that it is rate limiting for HCO 3 -fluxes and tha...

show abstract

Identification and cloning of the Na/HCO3− cotransporter (NBC) in human corneal endothelium

Cited by 22 publications

References 29 publications

Electrolyte and Fluid Transport in Mesothelial Cells

Electrolyte and Fluid Transport in Mesothelial Cells

Molecular expression and functional involvement of the bovine calcium-activated chloride channel 1 (bCLCA1) in apical HCO3− permeability of bovine corneal endothelium

Dependence of cAMP meditated increases in Cl− and HCO3− permeability on CFTR in bovine corneal endothelial cells

Contact Info

Product

Resources

About