REVERSED ANION SELECTIVITY IN CULTURED CYSTIC-FIBROSIS SWEAT-DUCT CELLS

The human genetic disease cystic fibrosis (CF) is characterized by defective epithelial Cl- conductance (G(Cl)). To distinguish the CF-affected G(Cl) from other Cl- channels, we have studied the properties of G(Cl) in normal and CF cells grown from explanted reabsorptive sweat ducts (RD). The cultured cells from normal subjects retained some of the typical duct cell properties. The Na+ conductance inhibitor amiloride hyperpolarized intracellular potentials (V(m)) by 10.4 +/- 1.6 mV (n = 12). Substitution of gluconate for Cl- depolarized V(m) by 15.5 +/- 1.1 mV (n = 33). The apparent G(Cl) (G'(Cl)) of normal cells was sensitive to adenosine 3',5'-cyclic monophosphate (forskolin, 10(-6) M), as evidenced by a significant increase (63%, n = 9) in the Cl- gradient induced depolarization, and more selective for Cl- than I- (substitution of Cl- by I- depolarized V(m) by 6.3 +/- 0.3 mV, n = 49). Although the cells from CF subjects were statistically indistinguishable from normal cells based on V(m) (-18.5 +/- 1.2 mV, n = 49 vs. -20.1 +/- 1.8 mV, n = 28), CF cells expressed differences in G'(Cl), responses to forskolin, and anion selectivity. CF cells had a significantly reduced G'(Cl) as indicated by blunted responses to imposed Cl- gradients (26% of normal, n = 28). In contrast to our observations in normal cells, the G'(Cl) of CF cells was insensitive to forskolin. Further, the residual G'(Cl) of CF cells was clearly distinguishable from the predominant G'(Cl) of normal cells because the anion selectivity of CF cells was reversed compared with normal, I- > Cl- (V(m) hyperpolarized by 3.9 +/- 0.4 mV, n = 15, when I- was substituted for Cl-). Although CF cells may be distinguished from normals by several properties, we found that this reversed anion selectivity was the most consistent and could be a new, highly reliable diagnostic marker for expression of the CF gene in vitro.