1 Department of Physiology, College of Medicine, University of South Alabama, Mobile, Alabama 36688; and 2 Department of Pharmacology, School of Medicine, University of North Carolina, Chapel Hill, North Carolina 27599
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ABSTRACT |
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Inhibitors of
Cl and
HCO
3 secretion reduce
acetylcholine-induced liquid, but not mucin, secretion by bronchial submucosal glands [S. K. Inglis, M. R. Corboz, A. E. Taylor, and S. T. Ballard. Am. J. Physiol. 272 (Lung Cell. Mol. Physiol. 16): L372-L377, 1997]. The present study quantified contributions
of Cl
and
HCO
3 transport to volume and
composition of acetylcholine-induced liquid secretion by airway
epithelium. When distal bronchi were excised from 33 pigs and treated
with 10 µM acetylcholine, the airways secreted 13.4 ± 0.7 µl · cm
2 · h
1.
Bumetanide (10 µM) pretreatment reduced acetylcholine-induced liquid
and Cl
secretion rates by
~70%, but HCO
3 secretion fell by
only 40%. Dimethylamiloride (DMA; 100 µM) pretreatment reduced
Cl
secretion rates by ~15%, but
HCO
3 secretion fell 47%. DMA alone
had little effect on liquid secretion. When airways were pretreated
with both bumetanide and DMA, acetylcholine-induced liquid secretion
was nearly abolished. We conclude that about three-fourths of
acetylcholine-induced liquid secretion in distal bronchi is dependent
on Cl
secretion. Most of
the remaining response is driven by
HCO
3 secretion. We speculate that the
principal source of this liquid is submucosal glands. Crossover
inhibition of bumetanide on HCO
3 secretion and DMA on Cl
secretion implies modulation of anion secretion secondary to changes in
cell electrolyte composition.
cystic fibrosis; dimethylamiloride; bumetanide; bronchi; submucosal glands; bicarbonate; chloride
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INTRODUCTION |
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THE LUMINAL SURFACE of the pulmonary airways is lined with a thin layer of liquid that normally approximates the depth of the cilia of airway surface epithelial cells. Islands of mucus rest atop this layer of liquid and are propelled by the cilia from distal airways toward the pharynx. It has been assumed that regulation of the depth of airway surface liquid (ASL) is critical to normal ciliary clearance functions. That is, if the depth of the ASL is too great, the tips of the cilia cannot contact the mucus and mucociliary transport is impeded. On the other hand, if the ASL depth is too shallow, the cilia become entangled in the mucus and transport efficiency is reduced. Therefore, adequate removal of inhaled and endogenous debris depends on regulation of ASL depth.
The dynamics of ASL are poorly understood. Whereas basal liquid
absorption by airway surface epithelia is driven by active Na+ transport (4), the mechanism
and site of liquid secretion in the airways remain controversial.
Specifically, surface epithelial cells have the capacity to secrete
Cl and liquid, but in most
species, this process is best demonstrated after inhibition of active
Na+ absorption (5). In contrast,
submucosal glands in nasal, tracheal, and bronchial airways of higher
mammals secrete copious quantities of mucus and liquid in response to
cholinergic or adrenergic stimulation (16, 22). Consequently,
submucosal glands could serve as a major source of ASL.
In cystic fibrosis (CF), mutations in the CF transmembrane conductance
regulator protein (CFTR), a cAMP-regulated
Cl channel (1), disable
Cl
secretion by airway
epithelia (17). Airway obstruction and increased susceptibility to
bacterial pulmonary infections that typify this disease have long been
thought, albeit without definitive evidence, to result from impaired
Cl
-dependent secretion of
ASL. CFTR is normally localized at high density to the serous cells of
the submucosal glands (8), suggesting that physiologically important
secretion of Cl
occurs at
this site. A previous study (11) showed that mucins accumulate in the
gland ducts of acetylcholine-treated porcine airways in the presence,
but not in the absence, of a combination of
Cl
and
HCO
3 secretion inhibitors. Inhibitor
pretreatment also substantially reduces the volume of mucus liquid
produced in response to acetylcholine and increases the solids content of mucus threefold (21). These findings support the notion that acetylcholine-induced glandular liquid secretion is driven by both
Cl
and
HCO
3 secretion and that inhibition of
this process uncouples liquid from mucin secretion by glands.
Interpretation of these studies depended on the putative selectivity of
the inhibitors because the ion composition of the secreted liquid was
not measured.
The present study was designed to 1)
measure the secretion rate and composition of liquid that accumulated
in lumens of excised distal airways pretreated with
acetylcholine and 2) evaluate the effects of inhibitors of active
Cl and
HCO
3 secretion on these properties.
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METHODS |
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Airway excision. Young pigs (10-15 kg) were obtained from a local vendor. Animals were sedated with an intramuscular injection of xylazine (80 mg) and ketamine (4 mg) and killed with an intravenous overdose of pentobarbital sodium. The chest was rapidly opened, and portions of both lungs were excised and placed in Krebs-Ringer bicarbonate (KRB) solution at room temperature. Distal bronchi (external diameter 2-3 mm, length 25-35 mm) were immediately dissected free from the surrounding tissue. Airway branches were tightly ligated with sutures close to the airway trunk to prevent leakage of liquid into the luminal space. The isolated bronchi were then warmed slowly (~0.1°C/min) from room temperature to 37°C.
Treatment with inhibitors of ion
secretion. The role of
Cl and
HCO
3 transport in
acetylcholine-induced liquid secretion was evaluated by exposing both
the luminal and submucosal surfaces of the bronchi to either 10 µM
bumetanide, an
Na+-K+-2Cl
cotransport inhibitor, or
Cl
-free KRB to block
Cl
secretion; or
dimethylamiloride (DMA; 100 µM), an
Na+/H+
exchange inhibitor, to block HCO
3
secretion. The action of DMA is thought to result from inhibition of
proton extrusion across the basolateral membrane, which reduces the
capacity of the epithelial cells to generate cytoplasmic
HCO
3 (19). We also exposed bronchi to
bilateral Na+-free KRB to inhibit
both
Na+-K+-2Cl
cotransport and
Na+/H+
exchange. Bilateral ouabain (1 mM), an
Na+-K+-ATPase
inhibitor, was used to inhibit primary
Na+ active transport and any
secondary transport that depends on Na+ and
K+ gradients across the cell
membrane. In each experiment, treated tissues were paired with control
(vehicle-treated) bronchi from the same animal.
Collection of airway liquid.
Bronchi were pretreated with inhibitors of ion
secretion for 45 min. Paired control airways were pretreated with an
equal volume of the vehicle dimethyl sulfoxide (DMSO) for the same
period of time. Tissues exposed to
Cl- or
Na+-free KRB solution were
incubated in these solutions before being warmed and were not
pretreated for an additional 45 min. During the pretreatment period,
the solutions bathed both the luminal and adventitial surfaces of each
bronchus. At the end of pretreatment, the airway was removed from the
bath and the lumen was cleared of all liquid and mucus. Both ends of
the airway were cannulated with polyethylene tubing, and the
preparation was returned to the pretreatment bath. Then, acetylcholine
(10 µM) was added to the bath solution to stimulate liquid secretion.
After 2 h, the bronchi were removed from the bath and cut lengthwise.
Mucus liquid in the airway lumens was collected with a 2-mm-diameter
glass rod and forceps. The non-Newtonian properties of mucus allow
secretions to be picked up and manipulated as a semisolid. Residual
liquid, if present in the lumens, was collected with a pipette. When
liquid was present in the cannulas, the liquid was gently cleared from the tubes with forced air. Collected liquid was transferred to tared
microcentrifuge tubes. The sealed specimens were weighed (Mettler H20
balance) and frozen for analysis. Liquid secretion rate
(JV) was
calculated from total secretion volume and normalized to the estimated
surface area. Luminal surface area (SA) was calculated from airway
length (L) and outer diameter
(D) by the following relationship:
SA = 0.682D
L.
Histological sections of six different distal bronchi showed that the
cross-sectional inner-surface circumference was 68.2 ± 2.6% of the outer-surface circumference (Trout, unpublished observations). This relationship between inner and outer
circumference is unaffected by constriction of airway smooth muscle due
to folding of the airway mucosa (Trout, unpublished observations).
Collected liquid volume (in ml) was considered to be equivalent to wet
weight (in g).
Ion analysis. Frozen specimens were
thawed and diluted with 1 ml of 0.2 N
HNO3 and 1 ml of distilled,
deionized water. Standards and blanks were similarly prepared. The
diluted, acidified specimens were divided into two 1-ml samples for
flame photometric analysis and amperometric
Cl titration. Specimens,
standards, and blanks were directly assayed for
Na+ and
K+ with a Coleman model 51 flame
photometer. To measure Cl
,
1-ml samples were combined with 1 ml of 0.1 N
HNO3, 2 ml of acid reagent, 0.2 ml
of glacial acetic acid, and 2 drops of indicator gelatin solution.
Then, the samples were amperometrically titrated with a Labconco
digital chloridimeter.
HCO3 in another set of frozen
specimens was measured by the method of Van Slyke as modified by
Bittner and Hall (2). Each specimen was thawed and diluted to 100 µl
with distilled, deionized water. Standards and blanks were prepared similarly. Each was combined with 900 µl of a bromcresol
green indicator solution and titrated to the indicator end
point with 0.005 N NaOH dispensed by an Oxford titrator (model 301).
Solutions and drugs. KRB solution was
composed of (in mM) 112 NaCl, 4.7 KCl, 2.5 CaCl2, 2.4 MgSO4, 1.2 KH2PO4,
25 NaHCO3, and 11.6 glucose.
Cl was replaced by
equimolar gluconate in
Cl
-free KRB.
Na+ was replaced by equimolar
choline in Na+-free KRB solution.
Solution pH was maintained in solutions by constant gassing with 95%
O2-5%
CO2. All drugs were purchased from
Sigma. Stock solutions of bumetanide, DMA, and ouabain were prepared
with DMSO. Stock solutions of acetylcholine were prepared with
deionized water.
Statistics. Data are expressed as means ± SE. Paired comparisons were made with either dependent or independent t-tests. Bonferroni corrections were made for multiple comparisons. Differences were considered to be significant when P < 0.05. The number of observations (animals) in each group is given by n.
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RESULTS |
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Liquid volume secretion. In the
absence of stimulation, bronchi secreted very little liquid (0.4 ± 0.2 µl · cm2 · h
1;
n = 6). When treated with 10 µM acetylcholine, however,
bronchi secreted 13.4 ± 0.7 µl · cm
2 · h
1
(n = 33). Liquid secretion was not transient but continuous, as indicated by the relatively constant rate of liquid accumulation in
the cannulas during the 2-h incubation. The acetylcholine-induced JV was
significantly reduced by 70% when airways were exposed to 10 µM
bumetanide (Table 1). Pretreatment with 100 µM DMA alone did not alter
JV (Table 1). The
JV of tissues
pretreated with both bumetanide and DMA decreased by 89% compared with
control bronchi, an effect that was significantly greater
than bumetanide pretreatment alone (Table 1).
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When bronchi were bathed in
Na+-free KRB before acetylcholine,
JV was virtually
abolished compared with airways bathed in
Na+-replete KRB (Table 1). A
similar change from the acetylcholine-stimulated control bronchi was
induced by exposing airways to 100 µM ouabain (Table 1). Compared
with airways bathed in KRB,
Cl-free KRB inhibited the
acetylcholine-induced
JV by 78% (Table 1), similar to the magnitude of inhibition induced by bumetanide pretreatment.
Ion analysis. Table
2 shows the ion composition of the luminal
liquid that accumulated in response to acetylcholine. The concentrations of ions in luminal liquid from control airways resemble
those of plasma except that the K+
concentration is about threefold higher. When airways were pretreated with DMA, the HCO3 concentration in
the liquid was significantly reduced. Reduction in the
HCO
3 concentration tended to be
compensated for by an increase in the Cl
concentration, but the
rise was not significant. Pretreatment of airways with bumetanide to
block Cl
secretion resulted
in a significant 229% increase in
HCO
3 concentration. The
Cl
concentration tended to
fall during exposure to bumetanide, but this difference was not
significant. We noted no appreciable change in
Na+ or
K+ concentration with either
pretreatment. Although osmolality was not measured in the present
study, summation of solution ions in Table 2 suggests that the
acetylcholine-induced secretion product is nearly isosmotic to normal
plasma (vehicle pretreatment = 303 µeq/l; DMA pretreatment = 310.1 µeq/l; and bumetanide pretreatment = 336.6 µeq/l).
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Net secretory flows of ions were calculated from the ion concentrations
in Table 2 and the
JV for the same
tissues. In this subset of tissues, DMA pretreatment decreased
JV to 91% of control levels, whereas bumetanide
pretreatment reduced
JV to 30% of
control levels (Table 3). Reductions in net
flux of Na+,
K+, and
Cl with DMA or bumetanide
pretreatment parallel fractional reductions in liquid volume secretion.
However, DMA pretreatment caused a fractionally smaller
HCO
3 secretion than that predicted
(about twice the decrease) from the change in
JV, whereas bumetanide pretreatment resulted in a greater
HCO
3 flux (about twice) than that
predicted by JV.
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DISCUSSION |
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In this study, either bumetanide pretreatment or
Cl-free buffer blocked
~70% of the liquid secretion response to acetylcholine. These
results suggest that Cl
transport is responsible for most of the liquid that is secreted in
response to acetylcholine and is consistent with the well-established model for Cl
secretion
first described by Silva et al. (18). According to this model,
Cl
enters across the
basolateral membrane of epithelial cells by Na+-K+-2Cl
cotransport, which uses the electrochemical gradient for
Na+ to drive cell
Cl
above its equilibrium.
Given a sufficient electrochemical driving force,
Cl
exits the cells through
apical membrane Cl
channels. A lumen negative transepithelial potential
difference (PD) draws cations,
predominantly Na+, through the
paracellular path. This model has been widely accepted for airway
epithelia (4, 17). Secretion of
Cl
can be raised either by
opening apical membrane Cl
channels or by opening basolateral
K+ channels, which increases the
electrical force that drives
Cl
efflux. Recent studies
(13, 14) with airway gland cells provide evidence that cholinergic
agonists open basolateral
Ca2+-activated
K+ channels and induce secretion
through the CFTR in the luminal membrane.
Most of the acetylcholine-induced liquid secretion that is bumetanide
insensitive is blocked by pretreatment with DMA. Because DMA inhibits
HCO3 secretion by this preparation, we
think HCO
3 secretion drives the
bumetanide-insensitive liquid secretion. These data are consistent with
the model for HCO
3 secretion proposed
by Smith and Welsh (19). According to this model, carbonic anhydrase
catalyzes the intracellular formation of
HCO
3 and
H+ from
CO2 and
H2O. Subsequent removal of
H+ from the intracellular space by
basolateral
Na+/H+
exchange leaves HCO
3 to exit in
exchange for another anion or coupled to the flow of a cation in the
same direction. Further validation of this model is drawn from our
observations that Na+-free
solution (which removes substrate for both
Na+-K+-2Cl
and
Na+/H+)
or ouabain (which disrupts transmembrane
Na+ and
K+ gradients) abolishes
acetylcholine-induced liquid secretion. The path(s) by which
HCO
3 exits bronchial epithelial cells
in our preparation cannot be determined from our data, but it has been
suggested that HCO
3 passes through the
CFTR in the apical membrane of respiratory epithelia (19). However, the
permeability of the CFTR to HCO
3 is
only about one-fourth that of
Cl
(15). The outwardly
rectifying Cl
channel is
less selective than the CFTR (20) but may not be capable of aggregate
open times that would support an HCO
3 flux equal to roughly one-third of the
Cl
flow through all channels.
It is not possible to conclude from these data the contribution of
HCO3 secretion to
acetylcholine-induced liquid secretion when
Cl
secretion is intact. In
Table 3, DMA inhibits ~9% of the liquid secretion rate compared with
control bronchi, but this difference is not significant. It is possible
that DMA alone inhibits a fraction of liquid secretion, but the
response could be masked by the variance between experimental and
control responses. On the other hand, HCO
3 secretion could be induced under
conditions where Cl
secretion is inhibited. Evidence for this notion arises from a
study of salivary glands (7) where furosemide decreases
liquid secretion by only 60% but increases
HCO
3 concentration in the secreted
liquid approximately fivefold. In the present study with porcine
bronchi, however, inhibition of
Cl
secretion with
bumetanide is associated with a decrease rather than an increase in
HCO
3 net flow (Table 3).
If HCO3 and
Cl
flow through the same
channel(s), selective inhibition of a process that ordinarily maintains cellular chemical activity of one species would be expected not to
change flow of the unaffected species through the channel. Alternatively, flow of the unaffected species could increase if the
anions "compete" for channel entry. Independent paths for HCO
3 and
Cl
flow across the luminal
membrane also project no change in unaffected anion flow. None of the
inhibitors we tested increased or preserved secretion of an anion
species, so our findings suggest a more complex process(es). Bumetanide
inhibited the acetylcholine-induced secretion of
Na+,
K+, and
Cl
by 68-74% but
reduced HCO
3 secretion by only 40%
(Table 3). Consequently, the fall in
Cl
secretion was partially
compensated for by the persistence of HCO
3 secretion. DMA reduced
HCO
3 secretion by 47% and
Na+ and
K+ secretion by 20-26% but
Cl
secretion by only 16%.
Even though the changes were smaller with DMA, there is
a tendency for Cl
secretion
to compensate for the loss of HCO
3 secretion. However, each inhibitor reduced secretion of all ion species. This could result from secondary effects of an inhibitor on
channel activity in the same cell (e.g., change in intracellular pH,
Na+, or
K+). Consequently, our results
are compatible with HCO
3 and
Cl
secretion through the
same cell but cannot distinguish HCO
3 flow through Cl
channels
from flow through an independent path. Observations by Inglis et al.
(11) and Trout et al. (21) that liquid secretion can be
uncoupled from mucus secretion imply that secretion by the serous cell
was the principal target of the inhibitors we tested. Modification of
secreted solution by another acinar cell type or a complex series of
processes in different gland regions (e.g., secretion by the acinus and
selective absorption/secretion by ducts) seems, with our current
limited knowledge, to be unnecessarily complicated. There are, however,
difficulties with the same-cell hypothesis. For example, inhibition of
basolateral Na+ entry through the
cotransporter by bumetanide would be expected to decrease the
intracellular Na+ concentration,
promote
Na+/H+
exchange, raise the cell HCO
3
concentration, and increase rather than decrease
HCO
3 secretion. Effects of injection
of ion channel inhibitors into duct and acinar lumens would help
resolve modes of gland secretion, but this approach has not been developed.
Surface epithelial cells could also affect the composition and volume
of liquid secreted in response to acetylcholine. We cannot dismiss this
possibility, but several lines of evidence suggest that this liquid
arises largely, if not entirely, from the submucosal glands. First,
cholinergic agonists have been shown to be efficacious stimulants of
gland secretion in intact airways (3, 16, 22). Second, pretreatment of
bronchi with inhibitors of
Cl and
HCO
3 secretion causes mucin to
accumulate in gland ducts after application of acetylcholine (9, 11). These results suggested indirectly that inhibitors of
Cl
and
HCO
3 secretion blocked glandular
liquid secretion and thereby uncoupled liquid and mucin secretion in glands. Third, cultured airway gland cells have been shown to secrete
liquid in response to cholinergic stimulation (13). Fourth,
acetylcholine stimulates secretory fluxes of
Na+ and
Cl
across excised canine
airways (6), which contain glands, but exerts no effect on fluxes of
these ions across excised rabbit trachea (12), which is aglandular.
Because inhibitors of Cl
and HCO
3 secretion also inhibit
acetylcholine-induced isotonic liquid secretion, we conclude that both
anions are capable of driving liquid and net counterion
flows. In the absence of inhibitors, we estimate that
distal bronchi secrete ~13.4
µl · cm
2 · h
1
in response to acetylcholine. A previous study (10) showed that
acetylcholine causes a 15 µA/cm2
increase in equivalent short-circuit current
(Isc) across distal bronchi. Assuming that the
increase in Isc represents a sustained active
anion secretion that drives secretion of isosmotic liquid, electrogenic
transport accounts for only ~3.9
µl · cm
2 · h
1
or ~29% of the measured liquid secretion. Because these tissues were
not clamped to zero PD, JV projected from
Isc would be expected to be reduced by ~20%
under open-circuit conditions (change in PD with acetylcholine ~5
mV). These data indicate that a substantial fraction of the liquid
secretion response to acetylcholine is electrically silent. Boucher and
Gatzy (6) also reported that acetylcholine-induced increases in
Na+ and
Cl
secretion across canine
airways were not accompanied by a large bioelectric response. They
concluded that acetylcholine-induced secretion across intact airways
was electrically silent and originated from glands.
The results of the present study imply that the mechanism of secretion
by porcine bronchi is similar to that of rabbit mandibular salivary
glands (7). About 60% of acetylcholine-stimulated liquid secretion
from salivary glands was blocked by furosemide, which, like bumetanide,
inhibits Cl secretion by
blocking
Na+-K+-2Cl
cotransport. Residual salivary liquid secretion required the presence
of HCO
3. The authors also observed that furosemide caused HCO
3
concentrations in salivary liquid to increase from 13 to 55-80 mM.
Unlike the present study, however, furosemide induced an increase
rather than a decrease in HCO
3
secretion, an observation more in keeping with expectations for anion
flow through the same channels. The study of rabbit salivary glands
also reported that carbonic anhydrase inhibitors block only about
one-half of the HCO
3-dependent salivary liquid flow. This finding is intriguing because Inglis et al.
(9) previously showed that gland ducts are occluded by exposure to the
combination of bumetanide and DMA but not to the combination of
acetazolamide and bumetanide.
From our visual inspection of the airway lumen, we are confident that
we collected a large fraction of the mucus and liquid from the air
space. We admit, however, that some of the ASL, particularly periciliary liquid, is not collected with this technique. Recently, we
modified our original technique by adding aspiration with a syringe and
attached polyethylene tubing to remove as much residual liquid as
possible from the airway surface. We found that the rates of liquid
secretion measured with the "improved" collection technique
(control: 17.3 ± 1.4 µl · cm2 · h
1;
bumetanide: 5.0 ± 0.7 µl · cm
2 · h
1;
bumetanide + DMA: 1.6 ± 0.2 µl · cm
2 · h
1)
are very similar to the rates presented in the present study (control:
13.5 ± 1.2 µl · cm
2 · h
1;
bumetanide: 4.0 ± 0.5 µl · cm
2 · h
1;
bumetanide + DMA: 1.9 ± 0.4 µl · cm
2 · h
1).
From these data, we feel confident that our original collection technique was quantitatively adequate.
In conclusion, we found that both
Cl and
HCO
3 can drive acetylcholine-induced
liquid secretion by distal bronchi. We think that this liquid emanates
from glands. Studies with inhibitors of anion transport show that all
agents reduce liquid and electrolyte secretion but that inhibition of
Cl
secretion tends to
maintain HCO
3 secretion, whereas
inhibition of HCO
3 secretion tends to preserve Cl
secretion. To
the extent that gland secretion contributes to the formation of ASL,
anion transport by gland epithelia would be expected to regulate ASL
volume and composition.
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ACKNOWLEDGEMENTS |
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We thank Dr. Richard C. Boucher for useful comments and
suggestions. We are particularly indebted to Dr. Michael R. Van Scott, who first raised our interest in the importance of
HCO3 transport by airway epithelia.
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FOOTNOTES |
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This work was supported by National Heart, Lung, and Blood Institute Grant HL-48622.
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. §1734 solely to indicate this fact.
Address for reprint requests: S. T. Ballard, Dept. of Physiology, MSB 3024, Univ. of South Alabama, Mobile, AL 36688.
Received 15 May 1998; accepted in final form 4 September 1998.
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REFERENCES |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
1.
Anderson, M. P.,
R. J. Gregory,
S. Thompson,
D. W. Sousa,
S. Paul,
R. C. Mulligan,
A. E. Smith,
and
M. J. Welsh.
Demonstration that CFTR is a chloride channel by alteration of its anion selectivity.
Science
253:
202-205,
1991[Medline].
2.
Bittner, O.,
and
S. G. Hall.
The titration of bicarbonate in plasmacritical factors.
Am. J. Clin. Pathol.
42:
522,
1964.
3.
Borson, D. B.,
R. A. Chin,
B. Davis,
and
J. A. Nadel.
Adrenergic and cholinergic nerves mediate fluid secretion from tracheal glands of ferrets.
J. Appl. Physiol.
49:
1027-1031,
1980
4.
Boucher, R. C.
Human airway ion transport, part one.
Am. J. Respir. Crit. Care Med.
150:
271-281,
1994[Medline].
5.
Boucher, R. C.
Human airway ion transport, part two.
Am. J. Respir. Crit. Care Med.
150:
581-593,
1994[Medline].
6.
Boucher, R. C.,
and
J. T. Gatzy.
Regional effects of autonomic agents on ion transport across excised canine airways.
J. Appl. Physiol.
52:
893-901,
1982
7.
Case, R. M.,
M. Hunter,
I. Novak,
and
J. A. Young.
The anionic basis of fluid secretion by the rabbit mandibular salivary gland.
J. Physiol. (Lond.)
349:
619-630,
1984[Abstract].
8.
Engelhardt, J. F.,
J. R. Yankaskas,
S. T. Ernst,
Y. Yang,
C. R. Marino,
R. C. Boucher,
J. A. Cohn,
and
J. M. Wilson.
Submucosal glands are the predominant site of CFTR expression in the human bronchus.
Nat. Genet.
2:
240-248,
1992[Medline].
9.
Inglis, S. T.,
M. R. Corboz,
and
S. T. Ballard.
Effect of anion secretion inhibitors on mucin content of airway submucosal gland ducts.
Am. J. Physiol.
274 (Lung Cell. Mol. Physiol. 18):
L762-L766,
1998
10.
Inglis, S. K.,
M. R. Corboz,
A. E. Taylor,
and
S. T. Ballard.
Regulation of ion transport across porcine distal bronchi.
Am. J. Physiol.
270 (Lung Cell. Mol. Physiol. 14):
L289-L297,
1996
11.
Inglis, S. K.,
M. R. Corboz,
A. E. Taylor,
and
S. T. Ballard.
Effect of anion transport inhibition on mucus secretion by airway submucosal glands.
Am. J. Physiol.
272 (Lung Cell. Mol. Physiol. 16):
L372-L377,
1997
12.
Jarnigan, F.,
J. D. Davis,
P. A. Bromberg,
J. T. Gatzy,
and
R. C. Boucher.
Bioelectric properties and ion transport of excised rabbit trachea.
J. Appl. Physiol.
55:
1884-1892,
1983
13.
Jiang, C.,
W. E. Finkbeiner,
J. H. Widdicombe,
and
S. S. Miller.
Fluid transport across cultures of human tracheal glands is altered in cystic fibrosis.
J. Physiol. (Lond.)
501:
637-647,
1997[Abstract].
14.
Moon, S.,
M. Singh,
M. E. Krouse,
and
J. J. Wine.
Calcium-stimulated Cl secretion in Calu-3 human airway cells requires CFTR.
Am. J. Physiol.
273 (Lung Cell. Mol. Physiol. 17):
L1208-L1219,
1997
15.
Poulsen, J. H.,
H. Fischer,
B. Illek,
and
T. E. Machen.
Bicarbonate conductance and pH regulatory capability of cystic fibrosis transmembrane conductance regulator.
Proc. Natl. Acad. Sci. USA
91:
5340-5344,
1994[Abstract].
16.
Quinton, P. M.
Composition and control of secretions from tracheal bronchial submucosal glands.
Nature
279:
551-552,
1979[Medline].
17.
Quinton, P. M.
Cystic fibrosis: a disease in electrolyte transport.
FASEB J.
4:
2709-2717,
1990
18.
Silva, P.,
J. Stoff,
M. Field,
L. Fine,
J. N. Forrest,
and
F. H. Epstein.
Mechanism of active chloride secretion by shark rectal gland: role of Na-K-ATPase in chloride transport.
Am. J. Physiol.
233 (Renal Fluid Electrolyte Physiol. 2):
F298-F306,
1977[Medline].
19.
Smith, J. J.,
and
M. J. Welsh.
cAMP stimulates bicarbonate secretion across normal, but not cystic fibrosis airway epithelia.
J. Clin. Invest.
89:
1148-1153,
1992[Medline].
20.
Tabcharan, J. A.,
T. J. Jensen,
J. R. Riordan,
and
J. W. Hanrahan.
Bicarbonate permeability of the outwardly rectifying anion channel.
J. Membr. Biol.
112:
109-122,
1989[Medline].
21.
Trout, L.,
M. King,
W. Feng,
S. K. Inglis,
and
S. T. Ballard.
Inhibition of airway liquid secretion and its effect on the physical properties of airway mucus.
Am. J. Physiol.
274 (Lung Cell. Mol. Physiol. 18):
L258-L263,
1998
22.
Ueki, I.,
V. F. German,
and
J. A. Nadel.
Micropipette measurement of airway submucosal gland secretion.
Am. Rev. Respir. Dis.
121:
351-357,
1980[Medline].