Distinct K+conductive pathways are required for Cl−and K+secretion across distal colonic epithelium

Abstract

Secretion of Cl−and K+in the colonic epithelium operates through a cellular mechanism requiring K+channels in the basolateral and apical membranes. Transepithelial current [short-circuit current ( Isc)] and conductance ( Gt) were measured for isolated distal colonic mucosa during secretory activation by epinephrine (Epi) or PGE2and synergistically by PGE2and carbachol (PGE2+ CCh). TRAM-34 at 0.5 μM, an inhibitor of KCa3.1 (IK, Kcnn4) K+channels (H. Wulff, M. J. Miller, W. Hänsel, S. Grissmer, M. D. Cahalan, and K. G. Chandy. Proc Natl Acad Sci USA 97: 8151–8156, 2000), did not alter secretory Iscor Gtin guinea pig or rat colon. The presence of KCa3.1 in the mucosa was confirmed by immunoblot and immunofluorescence detection. At 100 μM, TRAM-34 inhibited Iscand Gtactivated by Epi (∼4%), PGE2(∼30%) and PGE2+ CCh (∼60%). The IC50of 4.0 μM implicated involvement of K+channels other than KCa3.1. The secretory responses augmented by the K+channel opener 1-EBIO were inhibited only at a high concentration of TRAM-34, suggesting further that KCa3.1 was not involved. Sensitivity of the synergistic response (PGE2+ CCh) to a high concentration TRAM-34 supported a requirement for multiple K+conductive pathways in secretion. Clofilium (100 μM), a quaternary ammonium, inhibited Cl−secretory Iscand Gtactivated by PGE2(∼20%) but not K+secretion activated by Epi. Thus Cl−secretion activated by physiological secretagogues occurred without apparent activity of KCa3.1 channels but was dependent on other types of K+channels sensitive to high concentrations of TRAM-34 and/or clofilium.