Expression of nucleotide-regulated Cl(-) currents in CF and normal mouse tracheal epithelial cell lines

The dominant routefor Cl secretion in mouse tracheal epithelium is viaCl channels different from the cystic fibrosis (CF)transmembrane conductance regulator (CFTR), the channel that isdefective in CF. It has been proposed that the use of purinergicagonists to activate these alternative channels in human airways may bebeneficial in CF. In the present study, two conditionally immortalepithelial cell lines were established from the tracheae of micepossessing the tsA58 T antigen gene, one of which MTE18-(/)] washomozygous for a knockout of CFTR and the other MTE7b-(+/)]heterozygous for CFTR expression. In Ussing chamber studies, amiloride(10⁴ M) and a cocktail of cAMP-activating agents(forskolin, IBMX, and dibutyryl cAMP) resulted in small changes in theshort-circuit current (I_sc) and resistance ofboth cell lines, with larger increases in I_scbeing elicited by ionomycin (10⁶ M). Both cell linesexpressed P₂Y₂ receptors and responded to thepurinergic agonists ATP, UTP, and 5'-adenylylimidodiphosphate (10⁴ M) with an increase in I_sc.This response could be inhibited by DIDS and was abolished in thepresence of Cl-free Ringer solution. Reducing the mucosalCl concentration increased the response to UTP of bothcell lines, with a significantly greater increase in MTE18-(/)cells. Pretreatment of these cells with thapsigargin caused a directincrease in I_sc and inhibited the response toUTP. These data suggest that both cell lines expresspurinergic-regulated Cl currents and may prove valuabletools in studying the properties of this pathway.