G protein Gα(i-2) inhibits outwardly rectifying chloride channels in human airway epithelial cells

Previously we demonstrated that the heterotrimeric G protein, Gα(i-2), inhibits cystic fibrosis transmembrane conductance regulator (CFTR) chloride (Cl^-) channels in human airway epithelial cells (E. M. Schwiebert, F. Gesek, L. Ercolani, C. Wjasow, D. C. Gruenert, and B. A. Stanton. Am. J. Physiol. 267 (Cell Physiol. 36): C272-C281, 1994, and E. M. Schwiebert, N. L. Kizer, D. C. Gruenert, and B. A. Stanton. Proc. Natl. Acad. Sci. USA 89: 10623- 10627, 1992). The goal of the present study was to determine if G proteins also regulate outwardly rectifying Cl^- channels (ORCC), a distinct class of Cl^- channels regulated defectively by protein kinase A (PKA) in cystic fibrosis (CF). To this end, we used the patch-clamp technique to study ORCC in a normal human airway epithelial cell line (9HTEo^-) that expresses CFTR and ORCC. Stimulation of G proteins with GTP and GTPγS decreased the single- channel open probability (P(o)) of ORCC, whereas inhibition of G proteins by GDPβS increased the P(o). Moreover, pertussis toxin (PTX), an uncoupler of G(i) and G(o) subclasses of heterotrimeric G proteins, also increased the P(o). Purified Gα(i-2) decreased the P(o). In contrast, other PTX-sensitive G proteins, Gα(i-1), Gα(i-3), and Gα(o), had no effect on P(o). We propose that Gα(i-2) couples to a receptor whose agonist negatively regulates ORCC in human airway epithelial cells.