Modulation of Cl- secretion by benzimidazolones. II. Coordinate regulation of apical GCl and basolateral GK.
We previously demonstrated that the novel benzimidazolone, 1-ethyl-2-benzimidazolinone (1-EBIO), stimulates a sustained Cl- secretory response across T84 monolayers by opening a Ca(2+)-dependent basolateral K+ channel. In the present work, we evaluated the effects on Cl-secretion of other benzimidazolones, NS-004 and NS-1619, which have been shown to 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 (Isc). Neither NS-004 nor NS-1619 increased Isc subsequent to forskolin stimulation. However, when added after 1-EBIO, NS-004 and NS-1619 stimulated large sustained increases in Isc. In addition, NS-004 and NS-1619 potentiated the effects of carbachol. We used nystatin to permeabilize the apical or basolateral membrane to determine the effects of NS-004 and 1-EBIO on the basolateral K+ (IK) and apical Cl- (ICl) currents. Both NS-004 and 1-EBIO increased ICl, and the stimulated currents were inhibited by glibenclamide. In contrast, NS-004 failed to significantly affect IK, but subsequent addition of 1-EBIO induced a large increase in IK. The effects of 1-EBIO, NS-004, and NS-1619 on the Ca(2+)-dependent K+ channel (KCa) in T84 cells was determined in excised inside-out patches. Neither NS-004 nor NS-1619 affected K+ channel activity, whereas the subsequent addition of 1-EBIO produced a marked channel activation. Results similar to those observed in T84 monolayers were obtained from murine airway cell primary cultures: NS-004 or NS-1619 had no effect on Isc, whereas 1-EBIO stimulated a sustained Cl- secretory response. The results demonstrate that activation of CFTR alone is insufficient to evoke transepithelial Cl- secretion. Activation of the basolateral membrane K+ channel is a necessary component of the secretory response. Thus the basolateral membrane KCa may be a novel pharmacological target in cystic fibrosis therapy.
Devor
D C
DC
Department of Cell Biology and Physiology, University of Pittsburgh, Pennsylvania 15261, USA. dd2+@pitt.edu
Singh
A K
AK
Bridges
R J
RJ
Frizzell
R A
RA
D000818:Animals; D001562:Benzimidazoles / Q000494:pharmacology*; D002034:Bumetanide / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism; D002217:Carbachol / Q000494:pharmacology; D002460:Cell Line; D002462:Cell Membrane / Q000187:drug effects / Q000502:physiology*; D018999:Charybdotoxin / Q000494:pharmacology; D018118:Chloride Channels / Q000187:drug effects / Q000502:physiology*; D002712:Chlorides / Q000378:metabolism*; D002733:Chlorophenols / Q000494:pharmacology*; D005576:Colforsin / Q000494:pharmacology; D004357:Drug Synergism; D005905:Glyburide / Q000494:pharmacology; D007700:Kinetics; D008564:Membrane Potentials / Q000187:drug effects; D018408:Patch-Clamp Techniques; D013997:Time Factors
D001562:Benzimidazoles; D018118:Chloride Channels; D002712:Chlorides; D002733:Chlorophenols; D002034:Bumetanide; D018999:Charybdotoxin; C086491:NS 1619; D005576:Colforsin; C083230:NS 004; D002217:Carbachol; D005905:Glyburide; D002118:Calcium