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Am J Physiol Cell Physiol 279: C762-C770, 2000;
0363-6143/00 $5.00
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Vol. 279, Issue 3, C762-C770, September 2000

Modification of biophysical properties of lung epithelial Na+ channels by dexamethasone

A. Lazrak1,*, A. Samanta1,*, K. Venetsanou3, P. Barbry4, and S. Matalon1,2

Departments of 1 Anesthesiology and 2 Physiology and Biophysics, University of Alabama at Birmingham, Birmingham, Alabama 35233; 3 Intensive Care Unit, Athens Trauma Center, Kephesia, Greece; and 4 Institut de Pharmacologie Moléculaire et Cellulaire, Centre National de la Recherche Scientifique UPR411, 06560 Sophia Antipolis, France

There is considerable interest in identifying the basic mechanisms by which dexamethasone alters ion transport across the adult alveolar epithelium. Herein, we incubated synchronized A549 cells, a human alveolar epithelial cell line, with dexamethasone (1 µM) for 24-48 h. When normalized to HPRT (a housekeeping gene), A549 beta - and gamma -subunit mRNA levels for the human amiloride-sensitive epithelial sodium channel (hENaC), assessed by RT-PCR, increased by 1.6- and 17-fold respectively, compared with control values (P < 0.05). These changes were abolished by actinomycin D, indicating transcriptional regulation. Western blotting studies revealed that dexamethasone also increased expression of beta - and gamma -hENaC protein levels. In contrast, alpha -hENaC mRNA increased by onefold (P > 0.05) and alpha -hENaC protein level was unchanged. Incubation of A549 cells with dexamethasone increased their whole cell amiloride-sensitive sodium currents twofold and decreased the K0.5 for amiloride from 833 ± 69 to 22 ± 5.4 nM (mean ± SE; P < 0.01). Single channel recordings in the cell-attached mode showed that dexamethasone treatment increased single channel open time and open probability threefold and decreased channel conductance from 8.63 ± 0.036 to 4.4 ± 0.027 pS (mean ± SE; P < 0.01). We concluded that dexamethasone modulates the amiloride-sensitive Na+ channels by differentially regulating the expression of beta - and gamma -subunits at the mRNA and protein levels in the human A549 cell line, with little effect on alpha -hENaC subunit.

ENaC; lung; whole cell currents; single channels; A549 cells; amiloride; reverse transcription-polymerase chain reaction; Western blots

* A. Lazrak and A. Samanta contributed equally to this work and are listed in alphabetical order.




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