Modulation of cl- secretion by benzimidazolones. i. direct
activation of a ca2+-dependent k+ channel by 1-ethyl-2
-benzimidazolinone, 1-ebio.
Devor, Daniel C., Ashvani K. Singh, Raymond A. Frizzell, and Robert J.
Bridges.
Department of Cell Biology and Physiology, University of
Pittsburgh, Pittsburgh, PA 15261
APStracts 3:0131L, 1996.
We evaluated the effects of the novel benzimidazolone, 1-ethyl-2
-benzimidazolinone (1-EBIO) on Cl- secretion across T84 monolayers. 1
-EBIO stimulated a sustained Cl- secretory response at a half-maximal
effective concentration of 490 [mu]M. Charybdotoxin (CTX) inhibited
the 1-EBIO-induced Isc with a Ki of 3.6 nM, while 293B, an inhibitor
of cAMP-activated K+ channels, had no effect on the current induced
by 1-EBIO. In contrast, CTX failed to inhibit the 293B-sensitive,
forskolin-induced Isc. The above results suggested that 1-EBIO may be
activating the basolateral membrane Ca2+-dependent K+ channel (KCa)
in these cells. This was further confirmed using nystatin to
permeabilize the apical membrane in the presence of a mucosa-to
-serosa K+ gradient and determining the effects of 1-EBIO on the
basolateral IK. Under these conditions, 1-EBIO induced a large
increase in IK which was blocked by CTX. In membrane vesicles
prepared from T84 cells, 1-EBIO stimulated 86Rb+ uptake in a CTX
-sensitive manner; the Ki for inhibition by CTX was 3.5 nM. Similar to
our intact monolayer studies, this 86Rb+ uptake was not blocked by
293B. The effects of 1-EBIO on the KCa in T84 cells was determined in
excised inside-out patches. 1-EBIO (100 [mu]M) increased NPo from
0.09+/-0.03 to 1.17+/-0.27 (n=8); this effect on KCa activity
required a minimal level of free Ca2+. Similar to its effect on T84
cells, 1-EBIO stimulated a sustained Cl- secretory current in rat
colonic epithelium, which was partially blocked by CTX. Finally, 1
-EBIO stimulated a sustained Cl- secretory response in primary
cultures of murine tracheal epithelium. We conclude that the
benzimidazolone, 1-EBIO, stimulates Cl- secretion in secretory
epithelia via the direct activation of a KCa. 1-EBIO is the first
pharmacological opener of this important class of epithelial K+
channels to be identified.
Received 27 March 1996; accepted in final form 5 July 1996.
APS Manuscript Number L99-6.
Article publication pending Am. J. Physiol. (Lung Cell. Mol.
Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 21 August 1996