Properties and regulation of chloride channels in cystic fibrosis and normal airway cells.

The present study examines the properties of Cl- channels in cultured respiratory cells of cystic fibrosis (CF) patients and normal (N) individuals. In excised membrane patches the conductances for CF and N Cl- channels were larger at positive as compared to negative clamp voltages (Vc): 74 +/- 2.6 (Vc greater than 0) and 47 +/- 2.0 pS (Vc less than 0) for CF (n = 57) and 69 +/- 3.6 (Vc greater than 0) and 45 +/- 2.3 pS (Vc less than 0) for N (n = 35). The open probability (Po) of the channel increased markedly with depolarization. Both the voltage dependence of the conductance and of Po contribute to the outward rectification of the channel. The time histogram analysis reveals two open and two closed time constants. The selectivity of the channel was Cl- = Br- = I- greater than NO-3 much greater than gluconate. The channel was inhibited reversibly by 5-nitro-2-(3-phenylpropylamino)-benzoate (NPPB) at 10(-7) mol/l to 10(-5) mol/l. While Cl- channels were present in cell attached patches of N cells, they were absent in those of CF cells. The mean conductance for cell attached (N) Cl- channels was 76 +/- 3.2 pS for positive clamp voltages (Vc) and 46 +/- 3.9 pS for negative Vc (n = 8). When the membrane patches were excised from CF cells Cl- currents appeared spontaneously (n = 19). The immediate appearance (within 1 s) of Cl- channels after excision was observed at positive (n = 6) as well as at negative clamp voltage (n = 13). "Excision activation" of CF Cl- channels was observed at low (less than 10(-9) mol/l) or high (10(-3) mol/l) calcium activities on the cytosolic side of the excised patch. Variation of the Ca+ activity (less than 10(-9)-10(-3) mol/l) or pH (6.5-8.5) on the cytosolic side exerted no effects on these Cl- channels. These results suggest that Cl- channels are present in the apical membrane of CF and N respiratory cells but they seem to be inhibited in intact CF cells. Excision of the patch and hence removal of the cytosolic "inhibitor" leads to an activation of Cl- channels. The Cl- channels in excised patches of N and CF cells have identical properties.