MODULATION OF CL- SECRETION BY BENZIMIDAZOLONES .2. COORDINATE REGULATION OF APICAL G(CL) AND BASOLATERAL G(K)

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.