Characterization of K+ channels in the basolateral membrane of rat tracheal epithelia

To study K+ channels in the basolateral membrane of chloride-secreting epithelia, rat tracheal epithelial monolayers were cultured on permeable filters and mounted into an Ussing chamber system. The mucosal membrane was permeabilized with nystatin (180 mu g/ml) in the symmetrical high K+ (145 mM) Ringer solution. During measurement of the macroscopic K+ conductance properties of the basolateral membrane under a transepithelial voltage clamp, we detected at least two types of K+ currents: one is an inwardly rectifying K+ current and the other is a slowly activating outwardly rectifying K+ current. The inwardly rectifying K+ current is inhibited by Ba2+. The slowly activating K+ current was potentiated by cAMP and inhibited by clofilium, phorbol 12-myristae 13-acetate (PMA) and lowering temperature. This is consistent with the biophysical characteristics of I-SK channel. RT-PCR analysis revealed the presence of I-SK cDNA in the rat trachea epithelia. Although 0.1 mM Ba2+ only had minimal affect on shea-circuit current (I-sc) induced by cAMP in intact epithelia, 0.1 mM clofilium strongly inhibited it. These results indicate that I-SK might be important for maintaining cAMP-induced chloride secretion in the rat trachea epithelia.