Dc. Devor et al., MODULATION OF CL- SECRETION BY BENZIMIDAZOLONES .2. COORDINATE REGULATION OF APICAL G(CL) AND BASOLATERAL G(K), American journal of physiology. Lung cellular and molecular physiology, 15(5), 1996, pp. 785-795
We previously demonstrated that the novel benzimidazolone, 1-ethyl-2-b
enzimidazolinone (1-EBIO), stimulates a sustained Cl- secretory respon
se across T84 monolayers by opening a Ca2+-dependent basolateral K+ ch
annel. In the present work, we evaluated the effects on Cl- secretion
of other benzimidazolones, NS-004 and NS-1619, which have been shown t
o open cystic fibrosis transmembrane conductance regulator (CFTR) Cl-
channels. In contrast to 1-EBIO, neither NS-004 nor NS-1619 stimulated
a significant Cl- secretory current (I-sc). Neither NS-004 nor NS-161
9 increased I-sc subsequent to forskolin stimulation. However, when ad
ded after 1-EBIO, NS-004 and NS-1619 stimulated large sustained increa
ses in I-sc. In addition, NS-004 and NS-1619 potentiated the effects o
f carbachol. We used nystatin to permeabilize the apical or basolatera
l membrane to determine the effects of NS-004 and 1-EBIO on the basola
teral K+ (I-K) and apical Cl- (I-Cl) currents. Both NS-004 and 1-EBIO
increased I-sc and the stimulated currents were inhibited by glibencla
mide. In contrast, NS-004 failed to significantly affect I-K, but subs
equent addition of 1-EBIO induced a large increase in I-K. The effects
of 1-EBIO, NS-004, and NS-1619 on the Ca2+-dependent K+ channel (K-Ca
) in T84 cells was determined in excised inside-out patches. Neither N
S-004 nor NS-1619 affected K+ channel activity, whereas the subsequent
addition of 1-EBIO produced a marked channel activation. Results simi
lar to those observed in T84 monolayers were obtained from murine airw
ay cell primary cultures: NS-004 or NS-1619 had no effect on I-sc, whe
reas 1-EBIO stimulated a sustained Cl- secretory response. The results
demonstrate that activation of CFTR alone is insufficient to evoke tr
ansepithelial Cl- secretion. Activation of the basolateral membrane K channel is a necessary component of the secretory response. Thus the
basolateral membrane K-Ca, may be a novel pharmacological target in cy
stic fibrosis therapy.