Effects of Endothelin-1 on Epithelial Ion Transport in Human Airways
Sabine Blouquit,* Anouar Sari,* Alain Lombet, Michelle D’herbomez, Emmanuel Naline, Regis Matran,
and Thierry Chinet
Laboratoire de Biologie et Pharmacologie des Epithe ´liums Respiratoires, Boulogne; INSERM U339 UFR Saint Antoine,
Paris; De ´partement de Biophysique, University of Lille, Lille; Institut de Pharmacologie, Paris, France; and De ´partement
de Physiologie, University of Lille, Lille, France
Endothelin-1 (ET-1) exerts many biological effects in airways,
including bronchoconstriction, airway mucus secretion, cell
proliferation, and inflammation. We investigated the effect of
ET-1 on Na absorption and Cl secretion in human bronchial
epithelial cells. Addition of 10?7M ET-1 had no effect on the
inhibition of the short circuit current (Isc) induced by amiloride,
a Na channel blocker. Addition of 10?7M ET-1 to the apical bath
in the presence of amiloride increased Isc in cultured human
bronchial epithelial cells studied in Ussing chambers. No effect
ing that the involved ET-1 receptors are likely present only in
the apical membrane of the cells. Use of Cl-free solutions and
bumetanide reduced the ET-1–induced increases in Isc, indicat-
ing that ET-1 stimulates Cl secretion. The ET-1–induced increase
in Isc was prevented by exposure to the ETBreceptor antagonist
BQ-788 but not to the ETAreceptor antagonist BQ-123. ET-1 did
not raise intracellular Ca levels, but increased the intracellular
concentration of cAMP. These findings indicate that ET-1 is a
apically located ETB receptors and activation of the cAMP
Endothelin 1 (ET-1) belongs to a family of potent peptidic
vasoconstrictor agents that exert an array of biological ef-
fects in addition to constriction of the vascular smooth mus-
cle cells (1, 2). In airways, several studies have shown that
chial smooth muscle cells. ET-1 also acts on airway epithe-
lial cells. Animal studies have found that ET-1 increases
the cilia beat frequency, activates mucus secretion by sub-
mucosal glands, and stimulates the proliferation of epithe-
lial cells (3–7). In humans, ET-1 stimulates lactoferrin and
mucous glycoprotein release from serous and mucous cells
in cultured nasal mucosal explants (8), and may affect ex-
pression of genes in bronchial epithelial cells such as the
fibronectin gene (9). The presence of immunoreactive ET-1
(Received in original form July 5, 2002 and in revised form January 29,
*These authors contributed equally to the work presented in this article.
Address correspondence to: Professeur Thierry Chinet, Laboratoire de Bio-
logie et Pharmacologie des Epithe ´liums Respiratoires, UFR Paris Ile de
France Ouest, Universite ´ de Versailles Saint Quentin en Yvelines, Ho ˆpital
Abbreviations: intracellular free Ca concentration, [Ca]i; cyclic adenosine
monophosphate, cAMP; Dulbecco’s modified Eagle’s medium and Ham’s
F12 mixture, DMEM/F12; endothelin-1, ET-1; short circuit current, Isc;
Am. J. Respir. Cell Mol. Biol.Vol. 29, pp. 245–251, 2003
Originally Published in Press as DOI: 10.1165/rcmb.2002-0104OC on March 6, 2003
Internet address: www.atsjournals.org
and abundant binding sites for ET-1 in airways suggests
that this peptide is an important autocrine and/or paracrine
neuromodulator of airway functions (10, 11).
In view of these data, we raised the hypothesis that ET-1
may also contribute to the regulation of transepithelial ion
transport, another major function of human airway epithe-
lial cells. Airway epithelial ion transport processes regulate
the volume of airway surface liquid and airway secretions
(12). The net movement of salt and fluid across human
airway epithelium is generally regarded as the result of
two opposite active ion transports: Na absorption and Cl
secretion. Active Na absorption predominates in the basal
state and induces fluid absorption from the lumen. Active
Cl secretion is the driving force for fluid secretion in human
airways and can be stimulated by various agents, including
adenosine 3?,5?-cyclic monophosphate (cAMP)-activating
agents and purinergic agonistssuch as adenosine 5?-triphos-
ET-1 could affect Na absorption across human airway
epithelium because recently published data suggest that
ET-1 may be an important negative regulator of ENaC:
adult rats lacking functional ETBreceptor activity display
enhanced Na absorption in the distal nephron (13); further-
more, in vitro studies in cell lines expressing ENaC have
demonstrated that ET-1 potently inhibits ENaC via ETB
receptors, and that this effect is mediated by Src family
ET-1 could also participate in the regulation of Cl secre-
tion across human airway epithelium because intranasal
administration of ET-1 in allergic and nonallergic subjects
induces symptoms of rhinorrhea and increases the amount
of secretions (15) and because this peptide regulates Cl
secretion in other epithelia. However, the effects of ET-1
on epithelial Cl secretion–i.e., the nature of the effect (stim-
differ between tissues and between species. In human gall-
bladder, ET-1 inhibits cAMP-induced Cl secretion (16),
whereas in human intestine, ET-1 stimulates Cl secretion
in part via the activation of enteric nerves (17). In dog
airways, ET-1 increases electrogenic Cl secretion (3, 18,
of cyclooxygenase products such as PGE2.
The goal of this study was therefore to determine
whether ET-1 regulates active Na absorption and/or active
Cl secretion in human airway epithelium, and to describe
the mechanisms of ET-1–mediated regulation of transepi-
thelial ion transport. We used cultured human bronchial
epithelial cells to ensure that the effect of ET-1 on ion
transport would not be mediated by nonepithelial airway
mucosal cells and by airway nerves.
Blouquit, Sari, Lombet, et al.: Endothelin-1 and Epithelial Ion Transport in Human Airways251
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