Modulation of calcium-dependent chloride secretion by basolateral SK4-like channels in a human bronchial cell line

The human bronchial cell line16HBE14o-was used as a model of airway epithelial cells to study the Ca2+ -dependent Cl- secretion and the identity of K-Ca channels involved in the generation of a favorable driving force for Cl- exit. After ionomycin application, a calcium-activated short-circuit current (I-Sc) developed, presenting a transient peak followed by a plateau phase. Both phases were inhibited to different degrees by NFA, glybenclamide and NPPB but DIDS was only effective on the peak phase. Rb-86 effluxes through both apical and basolateral membranes were stimulated by calcium, blocked by charybdotoxin, clotrimazole and TPA. I-EBIO, a SK-channel opener, stimulated Rb-86 effluxes. Block of basolateral KCa channels resulted in I-SC inhibition but, while reduced, Is, was still observed if mucosal Cl- was lowered. Among SK family members, only SK4 and SK1 mRNAs were detected by RT-PCR. KCNQ1 mRNAs were also identified, but involvement of K-cAMP channels in Cl- secretion was unlikely, since cAMP application had no effect on Rb-86 effluxes. Moreover, chromanol 293B or clofilium, specific inhibitors of KCNQ1 channels, had no effect on cAMP-dependent I-Sc. In conclusion, two distinct components of Cl- secretion were identified by a pharmacological approach after a Ca-i(2+) rise. K-Ca channels presenting the pharmacology of SK4 channels are present on both apical and basolateral membranes, but it is the basolateral SK4-like channels that play a major role in calcium-dependent chloride secretion in 16HBE14o-cells.