1 Liver Center, Department of Internal Medicine, Yale University School of Medicine, New Haven, Connecticut 06520-8019; and 2 Evans Biomedical Research Center, Department of Medicine, Boston University School of Medicine, Boston, Massachusetts 02118-2518
![]() |
ABSTRACT |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Cholangiocytes absorb and secrete fluid,
modifying primary canalicular bile. In several
Cl-secreting epithelia,
Na+-K+-2Cl
cotransport is a
basolateral Cl
uptake pathway facilitating apical
Cl
secretion. To determine if cholangiocytes possess
similar mechanisms independent of
CO2/HCO
-dependent secretion in rat liver isolated polarized
bile duct units (IBDUs) by using videomicroscopy. Without
CO2/HCO
and inhibited by Na+-K+-2Cl
inhibitor bumetanide. Carbonic anhydrase inhibitor
ethoxyzolamide had no effect on FSK-stimulated secretion, indicating
negligible endogenous CO2/HCO
cotransport activity
was assessed by recording intracellular pH during NH4Cl
exposure. Bumetanide inhibited initial acidification rates due to
NH
cotransport activity
occurred without CO2/HCO
cotransport maintains high intracellular Cl
concentration. Intracellular cAMP concentration increases activate basolateral K+ conductance, raises apical Cl
permeability, and causes transcellular Cl
movement into
the lumen. Polarized IBDU cholangiocytes are capable of vectorial
Cl
-dependent fluid secretion independent of
HCO
cotransport,
Cl
/HCO
ammonia; cholangiocyte; bumetanide; barium; pH
![]() |
INTRODUCTION |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
ALTHOUGH HEPATOCYTES ARE
THE primary source of bile, ~10% of basal bile flow in rats
and up to 40% in humans originates from the bile duct epithelium.
Cholangiocytes comprising the small intralobular bile duct segments are
capable of absorptive and secretory functions that modify the
composition of canalicular bile (9). These segments are
the site of injury in several primary cholestatic disorders
(40). After common bile duct ligation in the rat, bile
duct epithelial cells proliferate with potentiation of spontaneous bile
flow. In this model, hormonal stimulation by secretin, which increases
biliary cAMP, increases both bile flow rate and HCO
In cholangiocytes, secretion stimulated by cAMP is believed to occur
largely via coupling of apical Cl conductance(s) and
Cl
/HCO
/HCO
conductance, consistent
with recycling of Cl
at the apical membrane via
Cl
/HCO
secretion
drives a component of HCO
concentration
([Cl
]i) above electrochemical equilibrium
would facilitate secretory functions (18). Indeed, in
several Cl
-secreting epithelia, a basolateral,
electroneutral, loop-diuretic-sensitive Na+-K+-2Cl
cotransporter
(20, 26), energized by Cl
and
Na+ gradients (23), functions to maintain high
[Cl
]i (48).
Bumetanide-sensitive Na+-K+-2Cl
cotransport processes have been described in a number of epithelial and
nonepithelial cells. In addition to their function in epithelial salt
transport, Na+-K+-2Cl
cotransporters participate in cell volume homeostasis (17) and regulation of cell proliferation (37). In certain
epithelia, e.g., rat parotid acinar cells, basolateral
Na+-K+-2Cl
cotransport, in
combination with linked Na+/H+ and
Cl
/HCO
uptake (18, 41). Typically, in
salt-secreting epithelia, activation of cAMP- and/or
Ca2+-sensitive apical Cl
channels increases
apical membrane Cl
permeability, resulting in active
movement of Cl
from the cell into the luminal space;
Na+ and water follow passively along electrochemical and
osmotic gradients, respectively (48, 49). Secretion can be
potentiated in certain tracheal and gut epithelia by basolateral cAMP-
and/or Ca2+-activated K+ channels; activation
of these K+ channels hyperpolarizes the cell, driving
potential-dependent Cl
secretion (30, 47).
Certain biliary epithelial cell lines have been described to possess
bumetanide-inhibitable Rb uptake (7).
Isolated bile duct units (IBDUs) are intact polarized epithelial
structures derived from intralobular ducts maintained in short-term
culture. IBDUs have been exploited as a model biliary epithelium in
which relative secretion can be quantitated using videomicroscopy
(35). In previous studies (35), stimuli that increased intracellular cAMP concentration resulted in substantial fluid secretion in the presence of
CO2/HCO secretion.
In the present communication, using videomicroscopy to assess the
volume of fluid secreted by IBDUs, we have identified a role for
Cl that is separate from the well-appreciated role of
CO2/HCO
.
Cl
-dependent secretion was, in turn, sensitive to serosal
Na+ and to bumetanide (50 µM), consistent with
participation of Na+-K+-2Cl
cotransport. Furthermore, Cl
-dependent secretion in the
absence of CO2/HCO
secretion.
Intracellular pH (pHi) records of cholangiocytes comprising IBDUs revealed bumetanide-sensitive NH
cotransport. In
addition, Na+-K+-2Cl
cotransport
activity was stimulated by forskolin and inhibited by bumetanide. In
the presence of CO2/HCO
-dependent as
well, but only partly stilbene sensitive and not inhibited at all by
bumetanide. When combined, the anion exchange inhibitor DIDS and
bumetanide together blocked forskolin-stimulated secretion completely,
consistent with Cl
/HCO
uptake pathway. These
results, derived largely from functional assays, identify the
importance of extracellular Cl
to secretion and suggest a
key role for HCO
secretion by biliary epithelium.
![]() |
METHODS |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Isolation of bile duct units.
With the full approval of the Yale University School of Medicine Animal
Care and Use Committee, we obtained male Sprague-Dawley rats weighing
200-250 g from Camm Laboratory Animals (Wayne, NJ). Bile
duct fragments (30-100 µM) were enzymatically isolated from rat
livers and plated on Matrigel-coated (Collaborative Biomedical, Bedford, MA) glass coverslips and incubated at 37°C in a 5%
CO2-air atmosphere with supplemented -MEM (GIBCO BRL,
Grand Island, NY), as described previously (35). The
culture medium was exchanged at 24 h, and adherent IBDUs were
utilized in experiments by 48-60 h after initial plating.
Quantitation of secretion by video imaging.
Coverslips with adherent IBDUs were placed in a temperature-controlled
superfusable chamber and transilluminated on the stage of an inverted
microscope equipped with Nomarski optics. Coverslips were screened for
single spherical IBDUs possessing a sharply defined luminal border at a
focal plane that delineated the greatest luminal area. A television
camera and computerized imaging system were used to obtain and store
magnified digital images of superfused IBDUs on an optical disk. IBDUs
were equilibrated with
CO2/HCO
Measurements using fluorescent dyes.
Cholangiocytes comprising IBDUs were loaded with the pH-sensitive dye
2',7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein (BCECF) by incubation with 10 µM of the membrane-permeant AM (BCECF-AM, Molecular Probes, Eugene, OR) for 10 min at 37°C. Coverslips
containing IBDUs were transferred to a temperature-controlled chamber
(37°C) on the stage of an inverted microscope and superfused with
either 1) CO2/HCO
Assessment of NH cotransport (15,
27, 38) where NH
General experimental procedures.
All experiments were performed at 37°C under isotonic (290 mosM)
conditions. The compositions of the
CO2/HCO and choline or NH
![]() |
RESULTS |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
As shown in Fig. 1, we first
assessed the role of extracellular Cl in
forskolin-induced secretion in IBDUs. We added 10 µM forskolin to
IBDUs superfused with Cl
-free HEPES-Ringer. We observed
no effect on secretion until Cl
(132 mM) was returned to
the HEPES-Ringer solution. Thereafter, luminal CSA doubled in 10 min
and increased further to 150% above baseline within 20 min. Thus
cAMP-stimulated secretion requires basolateral Cl
and
occurs in the absence of CO2/HCO
|
Cellular respiration generates a nominal amount of CO2 that
can be hydrated to HCO-dependent secretion. Acetazolamide
(500 µM), another carbonic anhydrase inhibitor, also did not inhibit
secretion in similar experiments (not shown). These results indicate
that neither ambient CO2/HCO
-dependent secretion observed in
this experiment.
To determine if Cl-dependent secretion in the absence of
HCO
cotransporter, IBDUs
were superfused with HEPES-Ringer free of Cl
,
Na+, and CO2/HCO
, Na+,
and HCO
was added to the solution in the
absence of Na+. However, after introduction of
Na+ (125 mM) to the Cl
-containing solution,
we observed a rapid rate of secretion to 40% above baseline. Thus
HCO
and Na+ transport
process.
|
As such, we next examined the effects of bumetanide (50 µM), a
specific inhibitor of Na+-K+-2Cl
cotransport on secretion. As shown in Fig.
3, under Cl
- and
CO2/HCO
was added to
the solution, luminal CSA increased 100% within 20 min. In contrast,
when 50 µM bumetanide was present (Fig. 3), forskolin-stimulated
secretion was inhibited by 55% (P < 0.01).
|
NH cotransporter
(15, 27, 39), and pHi measurements were used to characterize Na+-K+-2Cl
cotransport activity in the presence and absence of
CO2/HCO
cotransport both in
the absence and presence of CO2/HCO
|
|
We next examined the role of a possible basolateral cAMP-activated
K+ conductance on forskolin-stimulated fluid secretion in
IBDUs (49) by examining the effects of Ba2+.
As shown in Fig. 5, addition of 10 µM
forskolin to IBDUs superfused with Cl-free HEPES-Ringer
did not lead to net secretion after 5 min. When Cl
was
returned to the HEPES-Ringer solution, luminal CSA increased to 150%
above baseline within 30 min. In other experiments, the identical
protocol was repeated, but after 5 min of preincubation with, and in
the continuous presence of, 1 mM BaCl (Fig. 5). As in the control
experiments without Ba2+ (Fig. 5), exposure to forskolin in
the virtual absence of Cl
did not induce secretion until
132 mM Cl
was introduced to the bathing solution.
However, Ba2+ (1 mM) alone decreased forskolin-stimulated,
Cl
-dependent secretion by one-half (Fig. 5) compared with
controls (P < 0.05). Furthermore, when the identical
protocol was repeated in the presence of both 1 mM Ba2+ and
50 µM bumetanide (Fig. 5), net forskolin-stimulated,
Cl
-dependent secretion was not observed after 30 min.
|
Given the apparent importance of Cl to secretion in the
absence of CO2/HCO
plays in cAMP-stimulated fluid secretion
under physiological CO2/HCO
.
Surprisingly, bumetanide had no effect on secretion in the presence of
CO2/HCO
cotransport appears to function in the basolateral uptake of Cl
. Previous studies (3, 4) in IBDUs
revealed a stilbene-sensitive Cl
/HCO3
exchange stimulated by secretin. Thus to determine if a Cl
/HCO3 exchange process participates in
Cl
uptake, the effect of the anion exchange inhibitor
DIDS was examined. In the presence of
CO2/HCO
-dependent secretion
(n = 13, P < 0.03 vs. control, data
not shown). However, as shown in Fig. 7,
when combined with bumetanide, DIDS completely blocked
forskolin-stimulated secretion in the presence of Cl
and
CO2/HCO
|
|
Our assessments of secretion may have been confounded if paracellular
fluid movement was markedly affected during experiments. To determine
if paracellular permeability was increased by the removal and/or
readmission of Cl, forskolin, and/or bumetanide, we
performed a series of experiments using Texas red-dextran (40,000 MW)
in the bathing solution. Compared with a 20-min control period in
HEPES-Ringer (after which 88% of initially intact IBDUs continued to
exclude Texas red-dextran from their lumens, n = 17)
there was no significant difference in Texas red-dextran entry
after 1) 15 min in Cl
-free HEPES-Ringer
followed by 25 min in Cl
-containing HEPES-Ringer (94%
exclusion, n = 16), 2) 15 min in Cl
-free HEPES-Ringer followed by 25 min in
Cl
-containing HEPES-Ringer in the presence of 10 µM
forskolin during both periods (95% exclusion, n = 20),
or 3) 15 min in Cl
-free HEPES-Ringer followed
by 25 min in Cl
-containing HEPES-Ringer with 10 µM
forskolin and 50 µM bumetanide present during both periods (89%
exclusion, n = 24).
![]() |
DISCUSSION |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Cholangiocytes play an important role in modifying the composition
of canalicular bile through secretory and reabsorptive processes
(1, 42). Bile is particularly enriched with
HCO, and cAMP-induced
HCO
recycling mechanism that couples an apical
Cl
conductance with a Cl
/HCO3
exchange (3, 33). However, in the nominal absence of CO2/HCO
and Na+
dependent, consistent with transport of Na+ and
Cl
. Bumetanide, a loop diuretic inhibitor of
Na+-K+-2Cl
cotransport, decreased
cAMP-stimulated secretion in the absence of
CO2/HCO
.
Nonetheless, ~ 45% of stimulated secretion was not blocked by bumetanide, consistent with either the presence of 1) other
Na+-dependent, but HCO
uptake and/or 2)
potential-driven, serosal-to-mucosal Cl
(and
Na+, when present) movement due to activation of a
basolateral K+ efflux pathway. Basolateral
Ba2+, an inhibitor of K+ channels, decreased
stimulated secretion by ~50%, consistent with activation of
basolateral K+ conductance(s). A basolateral K+
channel activated by cAMP and/or Ca2+ would permit exit and
recycling of K+ taken up by basolateral
Na+-K+-2Cl
cotransport and
Na+-K+-ATPase (34). Stimulated
fluid secretion was entirely inhibited by the combination of bumetanide
and Ba2+, indicating that in the absence of
CO2/HCO
in
experiments in which BaCl was used, this concentration of Cl
, in the face of inhibited K+ channels, did
not support forskolin-stimulated secretion (Fig. 5). Furthermore, in
pHi studies of nonstimulated IBDUs, bumetanide inhibited
~25% of NH
cotransport has
been described in other epithelia, bumetanide is a relatively specific
inhibitor of Na+-K+-2Cl
cotransporters (26), and the finding of
bumetanide-sensitive NH
cotransport.
We used forskolin to evaluate cotransporter activity during
cAMP-induced secretion. Both in the absence and presence of
CO2/HCO
cotransport. Thus Na+-K+-2Cl
cotransport activity is increased during forskolin-induced secretion, more so in the absence than in the presence of
CO2/HCO
cotransport presumably
functions as a Cl
uptake mechanism that helps maintain
[Cl
]i above electrochemical equilibrium.
Previous studies in several other secretory epithelia have demonstrated
that secretagogues activate
Na+-K+-2Cl cotransport either
directly (12, 32, 39) or as secondary responses to apical
Cl
secretion (21, 22, 29). Normally, in the
presence of CO2/HCO
conductance to an apical
Cl
/HCO
secretion results largely from
recycling of secreted Cl
by apical
Cl
/HCO
may explain why we do not observe an increase in the
Na+-K+-2Cl
cotransporter activity
after forskolin stimulation in IBDUs perfused with KRB, because under
CO2/HCO
/HCO
, keeping [Cl
]i
relatively high. Alternatively, cAMP may also stimulate basolateral Na+-HCO
uptake systems that might be present.
Because in other secretory epithelia
Cl/HCO
uptake (18), we examined the effect of
bumetanide and DIDS, an inhibitor of anion transport (19),
on secretion under physiological CO2/HCO
, alternative
CO2/HCO
uptake must be present. DIDS alone inhibited
Cl
-dependent secretion by only 25%, whereas bumetanide
together with DIDS ablated stimulated secretion, strongly suggesting
that a stilbene-sensitive Cl
uptake pathway, i.e., a
Cl
/HCO
channel may be pathways for Cl
uptake in
cholangiocytes. Although previously described cAMP- or
Ca2+-activated Cl
channels in biliary
epithelial cells (13) might function as alternate pathways
for Cl
uptake, we did not observe
Cl
-dependent secretion in the absence of Na+
and CO2/HCO
cotransport under
CO2/HCO
The present findings are most consistent with basolateral
Na+-K+-2Cl cotransport that
exists in parallel with basolateral
Cl
/HCO
/HCO
entry across the basolateral
membrane. However, although IBDUs are a model epithelium in which cell
polarity and intercellular junctions are preserved, thus excluding
rapid entry of solutes such as DIDS into the luminal solution, DIDS
inhibition of apical Cl
exit and entry cannot be entirely
ruled out. Nevertheless, because Na+/H+
exchange is present on the basolateral membrane in cholangiocytes (11, 31, 43), we speculate that, as in parotid acinar
cells, a basolateral Cl
/HCO
-deficient suckling
mice, there is no deficit in stimulated small intestinal fluid
secretion, and it has been proposed that
Cl
/HCO
and Na+ uptake
(14).
On the basis of these findings, we propose an integrative model for
cAMP-stimulated Cl secretion in cholangiocytes (Fig.
8). In this model, basolateral Na+-K+-2Cl
cotransport and
Cl
/HCO
uptake mechanisms that maintain [Cl]i
above electrochemical equilibrium. Increases in [cAMP]i
lead to both an increase in apical membrane permeability to
Cl
and activation of a basolateral membrane
K+ conductance. As a result, electromotive forces move
Cl
into the lumen with attendant movement of
Na+ and water. HCO
/HCO
|
In summary, the present study provides evidence for the presence of a
secretory Na+-K+-2Cl cotransport
process in IBDUs from rat liver. Because it is feasible to isolate
enriched populations of intrahepatic biliary epithelial cells
(25), molecular identification of the specific isoform(s) of a bumetanide-sensitive cotransporter should be possible
(26).
![]() |
ACKNOWLEDGEMENTS |
---|
We thank Michelle Pate for assistance with cell isolation.
![]() |
FOOTNOTES |
---|
This study was supported by National Institute of Diabetes and Digestive and Kidney Diseases Grants KO8-DK-02410 (S. K. Singh) and R01-DK-25636 (J. L. Boyer), a Junior Faculty Research Award from Yale School of Medicine (S. K. Singh), and a Career Development Award from the Crohn's and Colitis Foundation of America (S. K. Singh). Cholangiocytes were isolated in the Cell Isolation and Culture Core of the Yale Liver Center supported by National Institute of Diabetes and Digestive and Kidney Diseases Grant P30-DK-34989.
Address for reprint requests and other correspondence: S. K. Singh, Dept. of Medicine, Boston Univ. School of Medicine, Ste. 504, Evans Biomedical Research Center, 650 Albany St., Boston, MA 02118-2518 (E-mail: satish.singh{at}bmc.org).
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 29 February 2000; accepted in final form 21 March 2001.
![]() |
REFERENCES |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
1.
Alpini, G,
Glaser S,
Robertson W,
Rodgers RE,
Phinizy JL,
Lasater J,
and
LeSage GD.
Large but not small intrahepatic bile ducts are involved in secretin-regulated ductal bile secretion.
Am J Physiol Gastrointest Liver Physiol
272:
G1064-G1074,
1997
2.
Alpini, G,
Lenzi R,
Sarkozi L,
and
Tavoloni N.
Biliary physiology in rats with bile ductular cell hyperplasia. Evidence for a secretory function of proliferated bile ductules.
J Clin Invest
81:
569-578,
1988[ISI][Medline].
3.
Alvaro, D,
Cho WK,
Mennone A,
and
Boyer JL.
Effect of secretion on intracellular pH regulation in isolated rat bile duct epithelial cells.
J Clin Invest
92:
1314-1325,
1993[ISI][Medline].
4.
Alvaro, D,
Mennone A,
and
Boyer JL.
Role of kinases and phosphatases in the regulation of fluid secretion and Cl/HCO
5.
Amlal, H,
Paillard M,
and
Bichara M.
NH
6.
Amlal, H,
and
Soleimani M.
K+/NH
7.
Basavappa, S,
Middleton J,
Mangel AW,
McGill JM,
Cohn JA,
and
Fitz JG.
Cl and K+ transport in human biliary cell lines.
Gastroenterology
104:
1796-1805,
1993[ISI][Medline].
8.
Bleich, M,
Schlatter E,
and
Greger R.
The luminal K+ channel of the thick ascending limb of Henle's loop.
Pflügers Arch
415:
449-460,
1990[ISI][Medline].
9.
Boyer, JL.
Bile duct epithelium: frontiers in transport physiology.
Am J Physiol Gastrointest Liver Physiol
270:
G1-G5,
1996
10.
Cho, WK,
Mennone A,
Rydberg SA,
and
Boyer JL.
Bombesin stimulates bicarbonate secretion from rat cholangiocytes: implications for neural regulation of bile secretion.
Gastroenterology
113:
311-321,
1997[ISI][Medline].
11.
Elsing, C,
Kassner A,
and
Stremmel W.
Sodium, hydrogen antiporter activation by extracellular adenosine triphosphate in biliary epithelial cells.
Gastroenterology
111:
1321-1332,
1996[ISI][Medline].
12.
Evans, RL,
and
Turner RJ.
Upregulation of Na+-K+-2Cl cotransporter activity in rat parotid acinar cells by muscarinic stimulation.
J Physiol (Lond)
499:
351-359,
1997[Abstract].
13.
Fitz, JG,
Basavappa S,
McGill J,
Melhus O,
and
Cohn JA.
Regulation of membrane chloride currents in rat bile duct epithelial cells.
J Clin Invest
91:
319-328,
1993[ISI][Medline].
14.
Flagella, M,
Clarke LL,
Miller ML,
Erway LC,
Giannella RA,
Andringa A,
Gawenis LR,
Kramer J,
Duffy JJ,
Doetschman T,
Lorenz JN,
Yamoah EN,
Cardell EL,
and
Shull GE.
Mice lacking the basolateral Na-K-2Cl cotransporter have impaired epithelial chloride secretion and are profoundly deaf.
J Biol Chem
274:
26946-26955,
1999
15.
Garvin, JL,
Burg MB,
and
Knepper MA.
Active NH
16.
Garvin, JL,
Burg MB,
and
Knepper MA.
Ammonium replaces potassium in supporting sodium transport by the Na-K-ATPase of renal proximal straight tubules.
Am J Physiol Renal Fluid Electrolyte Physiol
249:
F785-F788,
1985
17.
Geck, P,
and
Pfeiffer B.
Na-K-2Cl cotransport in animal cells: its role in volume regulation.
Ann NY Acad Sci
456:
166-182,
1985[Abstract].
18.
Greger, R.
The membrane transporters regulating epithelial NaCl secretion.
Pflügers Arch
432:
579-588,
1996[ISI][Medline].
19.
Grinstein, S,
Ship S,
and
Rothstein A.
Anion transport in relation to proteolytic dissection of band 3 protein.
Biochim Biophys Acta
507:
294-304,
1978[ISI][Medline].
20.
Haas, M.
The Na-K-Cl cotransporters.
Am J Physiol Cell Physiol
267:
C869-C885,
1994
21.
Haas, M,
and
McBrayer DG.
Na-K-Cl cotransport in nystatin-treated tracheal cells: regulation by isoproterenol, apical UTP, and [Cl]i.
Am J Physiol Cell Physiol
266:
C1440-C1452,
1994
22.
Haas, M,
McBrayer DG,
and
Yankaskas JL.
Dual mechanism for Na-K-Cl cotransport regulation in airway epithelial cells.
Am J Physiol Cell Physiol
264:
C189-C200,
1993
23.
Haas, M,
Schmidt WF,
and
McManus TJ.
Catecholamine-stimulated ion transport in duck red cells. Gradient effects in electrically neutral Na-K-2Cl co-transport.
J Gen Physiol
80:
125-147,
1982[Abstract].
24.
Henry, RP.
Multiple roles of carbonic anhydrase in cellular transport and metabolism.
Annu Rev Physiol
58:
523-538,
1996[ISI][Medline].
25.
Ishii, M,
Vroman B,
and
LaRusso NF.
Isolation and morphologic characterization of bile duct epithelial cells from normal rat liver.
Gastroenterology
97:
1236-1247,
1989[ISI][Medline].
26.
Kaplan, MR,
Mount DB,
and
Delpire E.
Molecular mechanisms of NaCl cotransport.
Annu Rev Physiol
58:
649-668,
1996[ISI][Medline].
27.
Kinne, R,
Kinne-Saffran E,
Schutz H,
and
Scholermann B.
Ammonium transport in medullary thick ascending limb of rabbit kidney: involvement of the Na-K-Cl cotransporter.
J Membr Biol
94:
279-284,
1986[ISI][Medline].
28.
Kurtz, I,
and
Balaban RS.
Ammonium as a substrate for Na-K-ATPase in rabbit proximal tubules.
Am J Physiol Renal Fluid Electrolyte Physiol
250:
F497-F502,
1986
29.
Lytle, C,
and
Forbush BF.
Is intracellular chloride the switch controlling Na-K-2Cl cotransport in shark rectal gland? (Abstract).
Biophys J
61:
A34,
1992.
30.
Mandel, KG,
McRoberts JA,
Beuerlein G,
Foster ES,
and
Dharmsathaphorn K.
Ba2+ inhibition of VIP- and A23187-stimulated Cl secretion by T84 cell monolayers.
Am J Physiol Cell Physiol
250:
C486-C494,
1986
31.
Marti, U,
Elsing C,
Renner EL,
Liechti-Gallati S,
and
Reichen J.
Differential expression of Na+,H+-antiporter mRNA in biliary epithelial cells and in hepatocytes.
J Hepatol
24:
498-502,
1996[ISI][Medline].
32.
Matthews, JB,
Smith JA,
Tally KJ,
Awtrey CS,
Nguyen H,
Rich J,
and
Madara JL.
Na-K-2Cl cotransport in intestinal epithelial cells. Influence of chloride efflux and F-actin on regulation of cotransporter activity and bumetanide binding.
J Biol Chem
269:
15703-15709,
1994
33.
McGill, JM,
Basavappa S,
Gettys TW,
and
Fitz JG.
Secretin activates Cl channels in bile duct epithelial cells through a cAMP-dependent mechanism.
Am J Physiol Gastrointest Liver Physiol
266:
G731-G736,
1994
34.
McRoberts, JA,
Beuerlein G,
and
Dharmsathaphorn K.
Cyclic AMP and Ca2+-activated K+ transport in a human colonic epithelial cell line.
J Biol Chem
260:
14163-14172,
1985
35.
Mennone, A,
Alvaro D,
Cho W,
and
Boyer JL.
Isolation of small polarized bile duct units.
Proc Natl Acad Sci USA
92:
6527-6531,
1995[Abstract].
36.
Nathanson, MH,
Burgstahler AD,
Mennone A,
Dranoff JA,
and
Rios-Velez L.
Stimulation of bile duct epithelial secretion by glybenclamide in normal and cholestatic rat liver.
J Clin Invest
101:
2665-2676,
1998
37.
Panet, R,
Markus M,
and
Atlan H.
Bumetanide and furosemide inhibited vascular endothelial cell proliferation.
J Cell Physiol
158:
121-127,
1994[ISI][Medline].
38.
Paulais, M,
and
Turner RJ.
Activation of the Na-K-2Cl cotransporter in rat parotid acinar cells by aluminum fluoride and phosphatase inhibitors.
J Biol Chem
267:
21558-21563,
1992
39.
Paulais, M,
and
Turner RJ.
Beta-adrenergic upregulation of the Na-K-2Cl cotransporter in rat parotid acinar cells.
J Clin Invest
89:
1142-1147,
1992[ISI][Medline].
40.
Roberts, SK,
Ludwig J,
and
Larusso NF.
The pathobiology of biliary epithelia.
Gastroenterology
112:
269-279,
1997[ISI][Medline].
41.
Robertson, MA,
and
Foskett JK.
Membrane crosstalk in secretory epithelial cells mediated by intracellular chloride concentration.
Jpn J Physiol
44 Suppl:
S309-S315,
1994[ISI][Medline].
42.
Sellinger, M,
and
Boyer JL.
Physiology of bile secretion and cholestasis.
Prog Liver Dis
9:
237-259,
1990[Medline].
43.
Singh, SK,
Boron WF,
Cavestro GM,
and
Boyer JL.
Distinct apical and basolateral Na-H exchangers in isolated perfused intrahepatic bile duct segments (Abstract).
Gastroenterology
112:
A1384,
1997[ISI].
44.
Strazzabosco, M,
and
Boyer JL.
Ion transporters that regulate intracellular pH and secretion in bile duct epithelial cells.
In: Biliary and Pancreatic Ductal Epithelia: Pathobiology and Pathophysiology, edited by Sirica AE,
and Longnecker DS.. New York: Marcel Dekker, 1997, p. 85-106.
45.
Strazzabosco, M,
Mennone A,
and
Boyer JL.
Intracellular pH regulation in isolated rat bile duct epithelial cells.
J Clin Invest
87:
1503-1512,
1991[ISI][Medline].
46.
Tseng, H,
and
Berk BC.
The Na/K/2Cl cotransporter is increased in hypertrophied vascular smooth muscle cells.
J Biol Chem
267:
8161-8167,
1992
47.
Welsh, MJ.
Evidence for basolateral membrane potassium conductance in canine tracheal epithelium.
Am J Physiol Cell Physiol
244:
C377-C384,
1983[Abstract].
48.
Welsh, MJ.
Intracellular chloride activities in canine tracheal epithelium. Direct evidence for sodium-coupled intracellular chloride accumulation in a chloride-secreting epithelium.
J Clin Invest
71:
1392-1401,
1983[ISI][Medline].
49.
Weymer, A,
Huott P,
Liu W,
McRoberts JA,
and
Dharmsathaphorn K.
Chloride secretory mechanism induced by prostaglandin E1 in a colonic epithelial cell line.
J Clin Invest
76:
1828-1836,
1985[ISI][Medline].