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1 Neuroscience, Cell Biology & Physiology, Wright State University Boonshoft School of Medicine, Dayton, Ohio, United States
* To whom correspondence should be addressed. E-mail: dan.halm{at}wright.edu.
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 (Isc) and conductance (Gt) were measured for isolated distal colonic mucosa during secretory activation by epinephrine (epi) or prostaglandin-E2 (PGE2) and synergistically by prostaglandin-E2 and carbachol (PGE2+CCh). TRAM-34 at 0.5µM, an inhibitor of KCa3.1 (IK, Kcnn4) K+ channels (Proc Nat Acad Sci USA 97:8151, 2000), did not alter secretory Isc or Gt in guinea pig or rat colon. The presence of KCa3.1 in the mucosa was confirmed by immuno-blot and immuno-fluorescence detection. At 100µM, TRAM-34 inhibited Isc and Gt activated by epi (~4%), PGE2 (~30%) and PGE2+CCh (~60%). The IC50 of 4.0µM implicated involvement of K+ channels other than KCa3.1. The secretory responses augmented by the K+ channel opener 1-EBIO were inhibited only at high concentration of TRAM-34, suggesting further that KCa3.1 was not involved. Sensitivity of the synergistic response (PGE2+CCh) to high concentration TRAM-34 supported a requirement for multiple K+ conductive pathways in secretion. Clofilium [100µM], a quaternary ammonium, inhibited Cl- secretory Isc and Gt activated 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+.
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