Renal Division and Membrane Biology Program, Department of Medicine, Brigham and Women's Hospital and Harvard Medical School, Boston, Massachusetts 02115
![]() |
ABSTRACT |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
First published August 15, 2001;
10.1152/ajprenal. 00021.2001.The proximal nephron possesses a
leaky epithelium with unique paracellular permeability properties that
underlie its high rate of passive NaCl and water reabsorption, but the
molecular basis is unknown. The claudins are a large family of
transmembrane proteins that are part of the tight junction complex and
likely form structural components of a paracellular pore. To localize
claudin-2 in the mouse kidney, we performed in situ hybridization using
an isoform-specific riboprobe and immunohistochemistry using a
polyclonal antibody directed against a COOH-terminal peptide. Claudin-2
mRNA and protein were found throughout the proximal tubule and in the
contiguous early segment of the thin descending limb of long-looped
nephrons. The level of expression demonstrated an axial increase from
proximal to distal segments. In confocal images, the subcellular
localization of claudin-2 protein coincided with that of the tight
junction protein ZO-1. Our findings suggest that claudin-2 is a
component of the paracellular pathway of the most proximal segments of
the nephron and that it may be responsible for their uniquely leaky permeability properties.
tight junction; paracellular transport; renal tubule; gene expression
![]() |
INTRODUCTION |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
THE PARACELLULAR PATHWAY
PLAYS a key role in the reabsorption of solutes by the renal
tubule, particularly in "leaky" nephron segments. In the proximal
tubule, approximately one-third of NaCl reabsorption is thought to be
passive and occur via paracellular transport (17). Active
transcellular reabsorption of Na+ and
HCO concentration that then drives diffusive
paracellular Cl
flux. This process is critically
dependent on the preferential permeability of the paracellular pathway
of the mid- and late proximal tubule for Cl
over
HCO
Recent studies have demonstrated that the paracellular permeability barrier in all cells is constituted by the tight junction, which is a complex of multiple structural proteins (6). One class of tight junction proteins that has recently been identified, the claudin family, is of particular interest (25). Claudins are likely to be important determinants of paracellular epithelial permeability for five reasons. First, claudins are transmembrane proteins and therefore contribute peptide domains that physically protrude into the intercellular space. Second, overexpression of a claudin in cultured epithelia has been shown to reduce paracellular permeability (12). Third, one isoform, claudin-16 (paracellin-1), is localized to the thick ascending limb and distal convoluted tubule of the kidney and, when mutated, causes autosomal-recessive hypomagnesemia with hypercalciuria, an inherited disorder that is likely due to defective paracellular divalent cation transport (24). Fourth, at least 20 mammalian isoforms of claudin have now been identified, and all of those that have been studied have been found to be highly expressed in some epithelial tissues, including the kidney (7, 18). Finally, different isoforms of claudin can form heteropolymeric tight junction strands in a single cell, and heterophilic paired interactions between cells, and therefore have the potential to generate considerable combinatorial diversity (9). We (29) and others (24, 25, 27) have therefore proposed that the combination of paracellular permeability properties to solutes and/or water that is unique to each epithelial tissue, and to each nephron segment within the renal tubule, is specified by the unique claudin isoform, or combination of isoforms, that is expressed.
To map the claudin isoforms expressed in each segment of the renal tubule, we have used in situ hybridization and immunofluorescent staining of mouse kidney cryosections. We now report that claudin-2, an isoform that is restricted to the kidney and liver (7), is highly and selectively expressed in the proximal renal tubule and early thin descending limb.
![]() |
METHODS |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Preparation of riboprobes. The full 693-bp coding region of mouse claudin-2 cDNA (GenBank accession no. AI789490) was amplified by PCR, cloned into pBluescript II KS(+), and verified by DNA sequencing. Digoxigenin-labeled sense and antisense cRNA probes were prepared by in vitro transcription and alkali hydrolyzed to a length of 200 nucleotides, as described previously (15). Unlabeled sense cRNA transcripts of claudin-2 to be used as targets in dot-blot studies were generated similarly, except that digoxigenin was omitted. Labeled and unlabeled transcripts of claudin-7 and claudin-14 (GenBank accession nos. AA521724 and AA261472, respectively), the homologous claudin isoforms, were generated similarly.
In situ and blot hybridization. In situ hybridization was performed on 5-µm sections of unperfused frozen mouse kidney, essentially as described previously (21). In brief, the cryosections were fixed with 4% paraformaldehyde at room temperature for 15 min and acetylated with acetic anhydride. They were then immersed in plastic slide mailers containing 200-350 ng/ml riboprobe in a buffer of 50% formamide, 5× standard sodium citrate (SSC), 2% blocking reagent (Boehringer Mannheim), 0.02% SDS, 0.1% N-laurylsarcosine at pH 7, and hybridized at 68°C for 17 h. The sections were then rinsed in three changes of 2× SSC followed by two high-stringency washes in 0.1× SSC for 30 min at 68°C. Sections were visualized using alkaline phosphatase-conjugated anti-digoxigenin Fab fragments (Boehringer Mannheim) and 5-bromo-4-chloro-3-indolylphosphate/nitroblue tetrazolium, according to the manufacturer's instructions. For double-labeling studies, the sections were washed three times in 1× PBS after color development, then directly incubated with the following tubule-specific markers: FITC-conjugated Lotus tetragonobulus agglutinin (LTA), 10 µg/ml (Sigma); polyclonal antibody to the thiazide-sensitive NaCl cotransporter, 1:500, and to the bumetanide-sensitive Na-K-2Cl cotransporter (BSC-1), 1:200 (kind gifts of Dr. Steven C. Hebert); and the E11 monoclonal antibody to the vacuolar H+-ATPase, undiluted (kind gift of Dr. Stephen L. Gluck). Antibody labeling was detected with the appropriate FITC-conjugated secondary antibody.
For dot-blots, 1-µl aliquots containing 0.01-1 ng of unlabeled sense cRNA were spotted directly onto nylon membrane (Duralon, Stratagene) and immobilized by ultraviolet cross-linking. Hybridization and washing of the blots were performed under the same conditions as for in situ hybridization, after which they were processed for detection using a chemiluminescent reagent (CPD-Star, Boehringer Mannheim), according to the manufacturer's instructions.Tissue culture and transient expression studies.
The full coding region of mouse claudin-2, except the translational
termination codon, was amplified by PCR, using a sense primer with an
upstream KpnI restriction site and Kozak consensus sequence
and an antisense primer with a downstream BamHI site, and
cloned into the KpnI-BamHI sites of a pcDNA3
"shell" vector with a downstream in-frame FLAG octapeptide epitope
tag followed by a stop codon (4) to generate a
COOH-terminal epitope-tagged mammalian expression construct. HEK-293
cells, cultured to 70-80% confluence on glass coverslips in
Dulbecco's modified Eagle's medium with 5% fetal bovine serum at
37°C in 5% CO2, were transiently transfected with the
claudin-2 expression construct, or pcDNA3 alone as a vector control,
using LipofectAMINE Plus Reagent (Life Technologies). After 24 h,
the cells were washed in PBS and fixed in methanol at 80°C for 10 min. Immunostaining was then performed, as described below, in the
presence of 0.3% Triton X-100.
In vitro translation and immunoblotting.
The two templates that worked optimally for translation were plasmid
constructs containing the coding region and in-frame COOH-terminal FLAG
epitope tag of claudin-2 in pcDNA3 (see above) and claudin-7 in the
pOX(+) vector, which has a -globin 5'-untranslated sequence and a
poly-A+ tail (4). In vitro translation was
performed with the TNT-coupled reticulocyte lysate system in the
presence of Transcend biotinylated lysine-tRNA (both from Promega) and
detected by streptavidin blotting, according to the manufacturer's
instructions. Translation of firefly luciferase (predicted molecular
mass, 61 kDa) was used as a positive control, and omission of the
template as a negative control. To isolate proteins from native tissue,
mouse kidney cortex was dissected and homogenized, and a crude membrane
preparation and soluble fraction were separated by differential
centrifugation at 47,000 g. Immunoblots were performed as
described previously (4). Rabbit polyclonal antiserum
raised against a synthetic peptide derived from the COOH terminal of
human claudin-2 and epitope affinity purified (Zymed) was used at a
concentration of 1 µg/ml.
Immunohistochemistry. Immunohistochemistry was performed on 5-µm mouse kidney cryosections essentially as described previously (15), except that perfusion-fixation with paraformaldehyde was not performed because we found that it obscured detection of the claudin-2 antigen. Instead, sections were postfixed for 15 min in 4% paraformaldehyde at room temperature, then washed in PBS before immunostaining. The claudin-2 primary antibody was used directly on unamplified sections at a concentration of 3 µg/ml; rabbit polyclonal aquaporin-1 antibody (kind gift of Dr. Dennis Brown) was used at 1:200, rat monoclonal ZO-1 antibody (kind gift of Dr. Bradley Denker) at 1:2, and M2 anti-FLAG monoclonal antibody (Sigma) at 1:100. In double-label colocalization experiments, a series of rigorous control studies were performed to exclude cross-reactivity between the two primary antibodies, as we have described in detail previously (15). Specifically for double-labeling with rabbit antibodies against claudin-2 and aquaporin-1, the sections were stained first with claudin-2 antibody at a low concentration (0.12 µg/ml, undetectable without amplification), after which the signal was amplified with the tyramide amplification system (TSA, NEN Life Sciences) and detected with a Cy3 fluorophore. The sections were then incubated with the aquaporin-1 antibody and detected without amplification using a fluorescein-conjugated anti-rabbit IgG secondary antibody. To counterstain for nuclear DNA, sections were mounted in Vectashield mounting medium containing propidium iodide (Vector Laboratories). Slides were visualized with a Bio-Rad MRC-1024 confocal krypton-argon laser scanning microscope. For double-labeled slides, images were acquired sequentially for each fluorophore in single-label mode to minimize "bleed-through" between channels. Each pair of images was then imported into Adobe Photoshop 3.0, where false color was added, and the pair was merged to generate dual-color images.
Peptide-blocking studies.
The COOH-terminal 47 residues (amino acids 184-230) of mouse
claudin-2 were amplified by PCR and cloned downstream of, and in-frame
with, the Escherichia coli
glutathione-S-transferase (GST) coding sequence under the
control of the lacZ promoter, using the bacterial expression vector
pGEX-4T (Amersham-Pharmacia Biotech). Transformants were grown in the
presence of isopropyl-
-D-thiogalactopyranoside to induce
synthesis of the GST-CLDN-2 fusion protein, harvested, lysed by
sonication, and isolated by affinity purification with glutathione-sepharose. Bacteria transformed with pGEX-4T alone were
used to generate control GST protein. In peptide-blocked immunofluorescence studies, GST or GST-CLDN-2 was mixed in a 3:1 molar
ratio with the claudin-2 antibody, incubated at room temperature for 30 min, and then applied to kidney sections.
![]() |
RESULTS |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
To determine the intrarenal localization of claudin-2 mRNA, we
first generated an antisense riboprobe to the coding region of the
claudin-2 sequence for in situ hybridization. Claudin-2 is a member of
a large multigene family. Claudin-7 and -14, two of its closest
homologs, share 44 and 54% nucleotide identity within the coding
region, respectively. To assess the specificity of our claudin-2
riboprobe, we generated dot-blots spotted with serial dilutions of
sense cRNA for claudin-2, -7, and -14 and hybridized them at high
stringency to our antisense riboprobes (Fig.
1). The claudin-2 antisense riboprobe was
able to detect 0.01 ng of claudin-2 without demonstrating any
cross-reaction with up to 1 ng of claudin-7 or -14, indicating at least
100-fold isoform specificity.
|
Using this probe, we performed in situ hybridization of mouse kidney
cryosections at high stringency. Labeling with the antisense probe was
detected in the majority of tubules in the cortex and outer stripe of
outer medulla, and in a few tubules in the inner stripe, but not in the
inner medulla (Fig. 2). No labeling was observed in negative control sections that were hybridized with a sense
probe. To determine the identity of the claudin-2-expressing tubules,
we developed a double-label technique in which sections were first
hybridized to the claudin-2 RNA probe, processed for colorimetric
detection, and then labeled with a fluorescent lectin conjugate or
antibody marker. Claudin-2 mRNA localized to tubules stained with the
lectin from LTA (Fig. 3, D and
E), a marker found on the apical and, to a lesser extent,
basolateral membrane of the proximal tubule (23).
Claudin-2 was absent from tubules that stained with antibodies to the
apical bumetanide-sensitive Na-K-2Cl cotransporter (Fig. 3,
F and G), the thiazide-sensitive NaCl
cotransporter (Fig. 3, H and I), and the vacuolar
proton pump (Fig. 3, J and K), indicating that it
was not expressed in thick ascending limb, distal convoluted tubule, or
collecting tubule, respectively.
|
|
Within the proximal tubule, claudin-2 mRNA was expressed in all of segments S1-S3 and coincided precisely with LTA staining in every tubule. Claudin-2 mRNA labeling was observable but weak in the S1 segments, identified as tubules emerging from the urinary pole of Bowman's capsule and contiguous with the parietal epithelium (Fig. 3A). Claudin-2 labeling was stronger in presumptive S2 convoluted segments in the cortical labyrinth and S3 segments, identified morphologically as straight, axially oriented tubules in the medullary rays of the cortex, and the outer stripe of the outer medulla (Fig. 3B). A subset of tubules in the inner stripe near the border with the outer stripe also demonstrated labeling, suggestive of expression in the early part of the thin descending limb of Henle's loop (Fig. 3C). In situ hybridization with probes to three other claudin isoforms showed completely different patterns of labeling (Enck AH and and Yu ASL, unpublished observations), suggesting the absence of cross-hybridization to homologous mRNA species at this stringency.
Because discrepancies between mRNA and protein localization have been
described for other genes, we confirmed our data on claudin-2
expression by immunofluorescent localization of the protein, using a
commercially available polyclonal antibody raised against a
COOH-terminal peptide. The COOH-terminal region diverges markedly
between all known claudin isoforms (maximum of 25% amino acid
identity), so antibodies raised against this region are likely to be
quite isoform- specific. By immunoblotting, we found that the claudin-2
antibody detected a band of approximately the expected size of 24.4 kDa
in mouse kidney cortex membranes (Fig.
4C). To confirm that the
antibody was indeed recognizing claudin-2, we generated a bacterial
fusion protein of GST with the COOH-terminal peptide of claudin-2 (Fig.
4A) and an in vitro translated claudin-2 protein (Fig.
4B). Both were positive by immunoblotting with the claudin-2
antibody, whereas their respective negative controls, GST alone and an
in vitro translation product in the absence of the template, were
clearly negative (Fig. 4C). Although claudin-7 was also
efficiently translated (Fig. 4B), its protein was not stained by the claudin-2 antibody (Fig. 4C), indicating that
our antibody is isoform specific. Furthermore, in cultured epithelial cells transiently overexpressing a FLAG epitope-tagged claudin-2 construct, our claudin-2 antibody stained plasma membranes, and particularly the intercellular junctions, in a pattern identical to
that observed using an antibody against the FLAG epitope (Fig. 5A).
|
|
By immunofluorescence of mouse kidney sections using this
antibody, moderate levels of claudin-2 staining were found in the majority of tubules throughout the cortex and the outer stripe of outer
medulla, strong staining in a subset of tubules in the inner stripe of
outer medulla, and absence of staining in the inner medulla (Fig.
6). There was no staining with nonimmune
serum (not shown), and staining with the claudin-2 antibody was blocked by preincubation with the fusion protein of GST with its cognate COOH-terminal peptide but not when preincubated with GST alone (Fig.
5B). Claudin-2 protein expression in the cortex and outer stripe colocalized to tubules that stained with LTA, indicating that
these are proximal tubules (Fig.
7A). Claudin-2 expression extended distally from the S3 segment of proximal tubules and became
markedly more intense in the upper segments of the thin descending
limb, where it colocalized to the same tubules that strongly express
aquaporin-1 (Figs. 6 and 7C). These tubule segments were
distributed diffusely in the region between the vascular bundles,
indicating that they are likely to be early segments of the descending
limbs of long-looped nephrons (TDL1) (11, 13). Claudin-2
expression ended abruptly near the border between outer and inner
medulla and was absent from late thin descending limbs (TDL2) (Figs. 6
and 7D).
|
|
Within the tubules, claudin-2 was clearly localized to the
lateral intercellular membrane (Fig. 7, A and B).
In both proximal tubules and thin descending limbs, it appeared to
colocalize with the ubiquitously expressed tight junction protein ZO-1
(Fig. 8), indicating that claudin-2 is
located at or very close to the zona occludens. The presence of tubules
(presumably distal in origin) that were positive for ZO-1 but
completely negative for apparent claudin-2 staining confirmed the
absence of artifacts due to antibody cross-reactivity or bleed-through
of fluorescence. In proximal tubules, moderate intracellular claudin-2
staining was also observed.
|
![]() |
DISCUSSION |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
We have used in situ hybridization and immunohistochemistry to localize expression of a single claudin isoform, claudin-2, within the mouse kidney. Because of the high degree of homology between claudin family members, it was important to ensure that our techniques were sufficiently specific to detect a single isoform. Our results by in situ hybridization are likely to be specific because we used the highest possible stringency (hybridization at 68°C in the presence of 50% formamide and washes at 68°C in 0.1× SSC) and also demonstrated that the claudin-2 antisense riboprobe showed no cross-reaction to its two closest homologs, claudin-14 and -7, by dot-blot hybridization under the same conditions. Our results by immunohistochemistry are likely to be specific because we used an antibody directed against the COOH terminal of claudin-2, which is poorly conserved between homologous family members. We confirmed that the antibody recognizes claudin-2 by immunoblot of mouse kidney cortex membranes, in vitro translated protein, and a bacterially expressed GST fusion protein with the claudin-2 COOH-terminal peptide, and by immunofluorescence staining of cultured cells transfected with claudin-2. Specific immunorecognition of claudin-2 was absent with nonimmune serum and was blocked specifically by the GST-CLDN2 fusion protein. Finally, we demonstrated that the antibody was isoform specific because it did not recognize in vitro translated protein of the closely homologous isoform, claudin-7.
The results we obtained by in situ hybridization and by immunohistochemistry were very similar and therefore nicely corroborate each other. We found that claudin-2 is expressed throughout the proximal tubule and in upper segments of the thin descending limb near the border of the inner and outer stripe of outer medulla. We believe that the latter areas represent the early segments of thin descending limbs of long-looped nephrons because they also stain very strongly for aquaporin-1, which is reported to be predominantly expressed in long loops (20), and because they are distributed diffusely in the interbundle region, whereas the descending limbs of short-looped nephrons are known to be closely associated with the vascular bundles in the mouse (11, 13). Both techniques demonstrated axial variation in claudin-2 expression, increasing from proximal to distal portions of this part of the tubule. By immunohistochemistry, claudin-2 was localized to the tight junction, as expected. A modest amount of staining was also found intracellularly in the proximal tubule and may represent an immature pool in the synthetic pathway, a reserve pool to be recruited to the tight junction only when needed, or simply cross-reactivity of the antibody to another intracellular epitope.
An important role for the paracellular pathway in passive NaCl
reabsorption by the proximal nephron was proposed 35 years ago by
Rector and colleagues (22). In the early proximal tubule, Na+ is reabsorbed transcellularly, primarily with
HCO and low (~0.4)
for HCO
over
HCO
and the development of a
lumen-positive electrical potential. This in turn drives further
reabsorption of Na+, passively via the paracellular route,
and therefore further osmotic water reabsorption (19).
Thus approximately one-third of all Na+ and water
reabsorption in the proximal tubule is dependent on a leaky but
anion-selective paracellular pathway. At the same time, significant
transtubular gradients for glucose, amino acids, and organic anions and
cations accumulate by the end of the proximal tubule, and so the
paracellular pathway must maintain a tight barrier against their backleak.
By contrast, the thin descending limb is widely thought to be a segment that lacks active, transcellular NaCl reabsorption and is impermeable to passive, paracellular NaCl transport but highly permeable to water, thus allowing it to play a key role in the generation of the medullary concentrating gradient according to the Kokko-Rector-Stephenson model (16). However, it is in fact a heterogeneous nephron segment in all species except the rabbit (11) and is composed of three ultrastructurally distinct cell types, type I in descending limbs of short-looped nephrons (SDL), type II in the early segments of the descending limb of long-looped nephrons largely in the inner stripe of outer medulla (TDL1), and type III in the late segments of the descending limb of long-looped nephrons (TDL2) confined to the inner medulla (2). Type II cells are quite different from types I and III and more closely resemble proximal tubule cells in that they are tall and have well-developed apical microvilli, abundant mitochondria, and a single intercellular tight junctional strand, all suggestive of a cell that is active in transcellular solute and water transport, while having a leaky paracellular pathway. Consistent with this, the TDL1 is unique among thin descending limb segments in expressing basolateral Na-K-ATPase (5, 28), luminal carbonic anhydrase (3), and both functional (14) and molecular (1) evidence of apical Na+-H+ exchange. Furthermore, the TDL1 has a very low transepithelial resistance (28) and a 10-fold higher passive Na+ permeability than either TDL2 or SDL (11). It is therefore likely that the TDL1, very much like the late proximal tubule, mediates both active transcellular and passive paracellular salt reabsorption concomitant with osmotic water reabsorption.
Interestingly, claudin-2 has been found to be expressed in a strain of the canine kidney cell line, Madin-Darby canine kidney (MDCK), that has a low transepithelial resistance but is absent from the high-resistance strain of MDCK. Transfection of claudin-2 into the high-resistance cells induced a dramatic reduction in transepithelial resistance (8), suggesting the intriguing possibility that claudin-2 may be able to reconstitute a relatively leaky paracellular pore. We therefore speculate that the role of claudin-2 in proximal tubule and the TDL1 may be to create a low-resistance paracellular shunt that is critical for passive NaCl reabsorption in these segments.
![]() |
ACKNOWLEDGEMENTS |
---|
We thank Dr. Dennis Brown for helpful discussions.
![]() |
FOOTNOTES |
---|
First published August 15, 2001;10.1152/ajprenal.00021.2001
Address for reprint requests and other correspondence: A. S. L. Yu, Renal Division, Brigham and Women's Hospital, 77 Ave. Louis Pasteur, Boston, MA 02115 (E-mail: ayu{at}rics.bwh.harvard.edu).
The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
Received 26 January 2001; accepted in final form 29 June 2001.
![]() |
REFERENCES |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
1.
Amemiya, M,
Loffing J,
Lotscher M,
Kaissling B,
Alpern RJ,
and
Moe OW.
Expression of NHE-3 in the apical membrane of rat renal proximal tubule and thick ascending limb.
Kidney Int
48:
1206-1512,
1995[ISI][Medline].
2.
Dieterich, HJ,
Barrett JM,
Kriz W,
and
Bulhoff JP.
The ultrastructure of the thin loop limbs of the mouse kidney.
Anat Embryol (Berl)
147:
1-18,
1975[ISI][Medline].
3.
Dobyan, DC,
Magill LS,
Friedman PA,
Hebert SC,
and
Bulger RE.
Carbonic anhydrase histochemistry in rabbit and mouse kidneys.
Anat Rec
204:
185-197,
1982[ISI][Medline].
4.
Dowland, LK,
Luyckx VA,
Enck AH,
Leclercq B,
and
Yu ASL
Molecular cloning and characterization of an intracellular chloride channel in the proximal tubule cell line, LLC-PK1.
J Biol Chem
275:
37765-37773,
2000
5.
Ernst, SA,
and
Schreiber JH.
Ultrastructural localization of Na+,K+-ATPase in rat and rabbit kidney medulla.
J Cell Biol
91:
803-813,
1981
6.
Fanning, AS,
Mitic LL,
and
Anderson JM.
Transmembrane proteins in the tight junction barrier.
J Am Soc Nephrol
10:
1337-1345,
1999
7.
Furuse, M,
Fujita K,
Hiiragi T,
Fujimoto K,
and
Tsukita S.
Claudin-1 and -2: novel integral membrane proteins localizing at tight junctions with no sequence similarity to occludin.
J Cell Biol
141:
1539-1550,
1998
8.
Furuse, M,
Furuse K,
Sasaki H,
and
Tsukita S.
Conversion of zonulae occludentes from tight to leaky strand type by introducing claudin-2 into Madin-Darby canine kidney I cells.
J Cell Biol
153:
263-272,
2001
9.
Furuse, M,
Sasaki H,
and
Tsukita S.
Manner of interaction of heterogeneous claudin species within and between tight junction strands.
J Cell Biol
147:
891-903,
1999
10.
Green, R,
and
Giebisch G.
Reflection coefficients and water permeability in rat proximal tubule.
Am J Physiol Renal Fluid Electrolyte Physiol
257:
F658-F668,
1989
11.
Imai, M,
and
Yoshitomi K.
Heterogeneity of the descending thin limb of Henle's loop.
Kidney Int
38:
687-694,
1990[ISI][Medline].
12.
Inai, T,
Kobayashi J,
and
Shibata Y.
Claudin-1 contributes to the epithelial barrier function in MDCK cells.
Eur J Cell Biol
78:
849-855,
1999[ISI][Medline].
13.
Kriz, W,
and
Koepsell H.
The structural organization of the mouse kidney.
Z Anat Entwicklungsgesch
144:
137-163,
1974[ISI][Medline].
14.
Kurtz, I.
Apical and basolateral Na+/H+ exchange in the rabbit outer medullary thin descending limb of Henle: role in intracellular pH regulation.
J Membr Biol
106:
253-260,
1988[ISI][Medline].
15.
Luyckx, VA,
Goda FO,
Mount DB,
Nishio T,
Hall A,
Hebert SC,
Hammond TG,
and
Yu ASL
Intrarenal and subcellular localization of rat CLC5.
Am J Physiol Renal Physiol
275:
F761-F769,
1998
16.
Masilamani, S,
Knepper MA,
and
Burg MB.
Urine concentration and dilution.
In: Brenner and Rector's The Kidney (6th ed.), edited by Brenner BM.. Philadelphia, PA: Saunders, 2000, p. 595-635.
17.
Moe, OW,
Berry CA,
and
Rector FC, Jr.
Renal transport of glucose, amino acids, sodium, chloride, and water.
In: Brenner and Rector's The Kidney (6th ed.), edited by Brenner BM.. Philadelphia, PA: Saunders, 2000, p. 375-416.
18.
Morita, K,
Furuse M,
Fujimoto K,
and
Tsukita S.
Claudin multigene family encoding four-transmembrane domain protein components of tight junction strands.
Proc Natl Acad Sci USA
96:
511-516,
1999
19.
Neumann, KH,
and
Rector FC, Jr.
Mechanism of NaCl and water reabsorption in the proximal convoluted tubule of rat kidney.
J Clin Invest
58:
1110-1111,
1976[ISI][Medline].
20.
Nielsen, S,
Pallone T,
Smith BL,
Christensen EI,
Agre P,
and
Maunsbach AB.
Aquaporin-1 water channels in short and long loop descending thin limbs and in descending vasa recta in rat kidney.
Am J Physiol Renal Fluid Electrolyte Physiol
268:
F1023-F1037,
1995
21.
Peng, JB,
Chen XZ,
Berger UV,
Vassilev PM,
Brown EM,
and
Hediger MA.
A rat kidney-specific calcium transporter in the distal nephron.
J Biol Chem
275:
28186-28194,
2000
22.
Rector, FC, Jr,
Martinez-Maldonado M,
Brunner FP,
and
Seldin DW.
Evidence for passive reabsorption of NaCl in proximal tubule of rat kidney.
J Clin Invest
45:
1060-1070,
1966[ISI].
23.
Schulte, BA,
and
Spicer SS.
Histochemical evaluation of mouse and rat kidneys with lectin-horseradish peroxidase conjugates.
Am J Anat
168:
345-362,
1983[ISI][Medline].
24.
Simon, DB,
Lu Y,
Choate KA,
Velazquez H,
Al-Sabban E,
Praga M,
Casari G,
Bettinelli A,
Colussi G,
Rodriguez-Soriano J,
McCredie D,
Milford D,
Sanjad S,
and
Lifton RP.
Paracellin-1, a renal tight junction protein required for paracellular Mg2+ resorption.
Science
285:
103-106,
1999
25.
Tsukita, S,
and
Furuse M.
Occludin and claudins in tight-junction strands: leading or supporting players?
Trends Cell Biol
9:
268-273,
1999[ISI][Medline].
26.
Vallon, V,
Verkman AS,
and
Schnermann J.
Luminal hypotonicity in proximal tubules of aquaporin-1-knockout mice.
Am J Physiol Renal Physiol
278:
F1030-F1043,
2000
27.
Wong, V,
and
Goodenough DA.
Paracellular channels (Abstract).
Science
285:
62,
1999
28.
Yoshitomi, K,
and
Imai M.
Electrophysiological characterization of upper portion of descending limb of long-looped nephron.
Am J Physiol Renal Fluid Electrolyte Physiol
260:
F311-F316,
1991
29.
Yu, AS.
Paracellular solute transport: more than just a leak?
Curr Opin Nephrol Hypertens
9:
513-515,
2000[ISI][Medline].