Interleukin (IL)-13 (10 ng/ml for 48 h) treatment of human bronchial epithelial cells induced a hypersecretory ion transport phenotype. Ussing chamber experiments demonstrated that this phenotypic change was characterised by an almost complete inhibition of the amiloride-sensitive short circuit current (ISC) and the appearance of an enhanced calcium-activated chloride conductance (CaCC). The peak increases in ISC (anion secretion) in response to UTP and ionomycin were increased by >8 fold and >13 fold respectively following IL-13 treatment. Changes in intra-cellular Ca2+ levels following agonist exposure were not different between control and IL-13 treatments. The sensitivity of this IL-13-enhanced CaCC to several chloride channel-blocking molecules was determined following permeabilisation of the basolateral membrane and the establishment of a basolateral to apical chloride gradient. Under these conditions changes in ISC were regulated exclusively by the apical membrane and the current stimulated by ionomycin was sensitive to the chloride channel blockers diisothocyanatostilbene-2,2'-disulfonic acid (DIDS), dinitrostilben-2,2'-disulfonic acid (DNDS) and 5-nitro-2-(3-phenylpropylamino)benzoic acid (NPPB) but was insensitive to tamoxifen. An understanding of the pharmacological profile of this conductance will ultimately aid in the determination of its molecular identity and function in the human airway epithelium.
