An immortal cell line to study the role of endogenous CFTR in electrolyte absorption

The intact human reabsorptive sweat duct (RD) has been a reliable model for investigations of the functional role of “endogenous” CFTR (cystic fibrosis transmembrane conductance regulator) in normal and abnormal electrolyte absorptive function. But to overcome the limitations imposed by the use of fresh, intact tissue, we transformed cultured RD cells using the chimeric virus Ad5/SV40 1613 ori-. The resultant cell line, RD2(NL), has remained differentiated forming a polarized epithelium that expressed two fundamental components of absorption, a cAMP activated Cl− conductance (Gcl) and an amiloride-sensitive Na+ conductance (GNa). In the unstimulated state, there was a low level of transport activity; however, addition of forskolin (10−5 M) significantly increased the Cl− diffusion potential (Vt) generated by a luminally directed Cl− gradient from − 15.3 ± 0.7 mV to −23.9 ± 1.1 mV,n=39; and decreased the transepithelial resistance (Rt) from 814.8 ± 56.3 Ω.cm2 to 750.5 ± 47.5 Ω.cm2,n=39, (n=number of cultures). cAMP activation, anion selectivity (Cl−>I−>gluconate), and a dependence upon metabolic energy (metabolic poisoning inhibited GCl), all indicate that the GCl expressed in RD2(NL) is in fact CFTR-GCl. The presence of an apical amiloride-sensitive GNa was shown by the amiloride (10−5 M) inhibition of GNa as indicated by a reduction of Vt and equivalent short circuit current by 78.0 ± 3.1% and 77.9 ± 2.6%, respectively, and an increase in Rt by 7.2 ± 0.8%,n=36. In conclusion, the RD2(NL) cell line presents the first model system in which CFTR-GCl is expressed in a purely absorptive tissue. It provides an opportunity to study the properties and role of CFTR in the context of absorptive function in immortalized epithelial cells.