Benzimidazolones enhance the function of epithelial Na⁺ transport.
OBJECTIVE
Pharmacological enhancement of vectorial Na⁺ transport may be useful to increase alveolar fluid clearance. Herein, we investigated the influence of the benzimidazolones 1-ethyl-1,3-dihydro-2-benzimidazolone (1-EBIO), 5,6-dichloro-1-EBIO (DC-EBIO) and chlorzoxazone on vectorial epithelial Na⁺ transport.


METHODS
Effects on vectorial Na⁺ transport and amiloride-sensitive apical membrane Na⁺ permeability were determined by measuring short-circuit currents (I(SC)) in rat fetal distal lung epithelial (FDLE) monolayers. Furthermore, amiloride-sensitive membrane conductance and the open probability of epithelial Na⁺ channels (ENaC) were determined by patch clamp experiments using A549 cells.


RESULTS
I(SC) was increased by approximately 50% after addition of 1-EBIO, DC-EBIO and chlorzoxazone. With permeabilized basolateral membranes in the presence of a 145:5 apical to basolateral Na⁺ gradient, the benzimidazolones markedly increased amiloride-sensitive I(SC). 5-(N-Ethyl-N-isopropyl)amiloride-induced inhibition of I(SC) was not affected. The benzamil-sensitive I(SC) was increased in benzimidazolone-stimulated monolayers. Pretreating the apical membrane with amiloride, which inhibits ENaC, completely prevented the stimulating effects of benzimidazolones on I(SC). Furthermore, 1-EBIO (1 mM) and DC-EBIO (0.1 mM) significantly increased (threefold) the open probability of ENaC without influencing current amplitude. Whole cell measurements showed that DC-EBIO (0.1 mM) induced an amiloride-sensitive increase in membrane conductance.


CONCLUSIONS
Benzimidazolones have a stimulating effect on vectorial Na⁺ transport. The antagonist sensitivity of this effect suggests the benzimidazolones elicit this action by activating the highly selective ENaC currents. Thus, the results demonstrate a possible new strategy for directly enhancing epithelial Na⁺ transport.
Division of Neonatology, University of Leipzig, Leipzig, Germany.
M
M
Laube
S U
SU
Kimpel
P
P
Dietl
U H
UH
Thome
O H
OH
Wittekindt
D000818:Animals; D001562:Benzimidazoles / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D002460:Cell Line; D002463:Cell Membrane Permeability / Q000187:drug effects; D016764:Cell Polarity / Q000187:drug effects; D002478:Cells, Cultured; D002753:Chlorzoxazone / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D062708:Epithelial Sodium Channel Agonists / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D062686:Epithelial Sodium Channel Blockers / Q000494:pharmacology; D053503:Epithelial Sodium Channels / Q000378:metabolism*; D005333:Fetus / Q000166:cytology; D006801:Humans; D008564:Membrane Potentials / Q000187:drug effects; D018408:Patch-Clamp Techniques; D011650:Pulmonary Alveoli / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D051381:Rats; D020545:Respiratory Mucosa / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D059010:Single-Cell Analysis; D012964:Sodium / Q000378:metabolism
C507351:5,6-dichloro-1-ethyl-1,3-dihydro-2H-benzimidazol-2-one; D001562:Benzimidazoles; D062708:Epithelial Sodium Channel Agonists; D062686:Epithelial Sodium Channel Blockers; D053503:Epithelial Sodium Channels; D012964:Sodium; D002753:Chlorzoxazone; C102635:1-ethyl-2-benzimidazolinone