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 (I(sc))] and conductance (G(t)) were measured for isolated distal colonic mucosa during secretory activation by epinephrine (Epi) or PGE(2) and synergistically by PGE(2) and carbachol (PGE(2) + CCh). TRAM-34 at 0.5 microM, an inhibitor of K(Ca)3.1 (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 I(sc) or G(t) in guinea pig or rat colon. The presence of K(Ca)3.1 in the mucosa was confirmed by immunoblot and immunofluorescence detection. At 100 microM, TRAM-34 inhibited I(sc) and G(t) activated by Epi ( approximately 4%), PGE(2) ( approximately 30%) and PGE(2) + CCh ( approximately 60%). The IC(50) of 4.0 microM implicated involvement of K(+) channels other than K(Ca)3.1. The secretory responses augmented by the K(+) channel opener 1-EBIO were inhibited only at a high concentration of TRAM-34, suggesting further that K(Ca)3.1 was not involved. Sensitivity of the synergistic response (PGE(2) + CCh) to a high concentration TRAM-34 supported a requirement for multiple K(+) conductive pathways in secretion. Clofilium (100 microM), a quaternary ammonium, inhibited Cl(-) secretory I(sc) and G(t) activated by PGE(2) ( approximately 20%) but not K(+) secretion activated by Epi. Thus Cl(-) secretion activated by physiological secretagogues occurred without apparent activity of K(Ca)3.1 channels but was dependent on other types of K(+) channels sensitive to high concentrations of TRAM-34 and/or clofilium.

Bestrophin-2 mediates bicarbonate transport by goblet cells in mouse colon

“…CFTR is known to regulate a variety of ion channels and transporters, including CaCCs (46), and there may simply be compensatory changes in expression of other channels, including Best2. Finally, the idea that membrane hyperpolarization is required for a cholinergic response is not universal: cholinergic agonists can stimulate anion secretion when the membrane potential is clamped at a depolarized level (6) and when K Ca 3.1 channels are blocked pharmacologically (9). Although species differences may explain some discrepancies, the mechanisms of cholinergic action in colon are clearly murky.…”

“…However, the mechanisms underlying the Ca 2+ -stimulated anion current are unclear (3). One school of thought favors a role for Ca 2+ -activated Cl -channels (6,9), whereas another believes that Ca 2+ activates K Ca 3.1 K + channels that hyperpolarize the membrane and increase the driving force for anion secretion through CFTR (10)(11)(12)(13).…”

Adrenergic activation of electrogenic K+ secretion in guinea pig distal colonic epithelium: desensitization via the Y2-neuropeptide receptor

“…Three modes of electrogenic ion secretion (11,25,33,49,52) were stimulated by secretagogs to examine the action of the neuroendocrinepeptide PYY, epinephrine for modulatory mode, PGE 2 for flushing mode, and PGE 2 ϩ carbachol (CCh) for synergistic mode. Adding PYY to the serosal bathing solution during the basal quiescent state reduced the negative I sc toward zero and decreased G t (Fig.…”

“…A mode of ion secretion particularly evident in the distal colon is electrogenic K ϩ secretion, which can be stimulated via ␤-adrenergic activation (23,27,42,52) from the sympathetic nervous system (17,26,45). This modulatory mode of secretion occurs with minimal sustained Cl Ϫ secretion, which distinguishes it from the well-studied flushing mode that exhibits high rates of sustained electrogenic Cl Ϫ secretion (25,33,39). A sympathetic response in the distal colon therefore includes a sustained electrogenic K ϩ secretion in concert with the slowing of motility and vasoconstriction that diverts blood away from the gut.…”

Genomic Priming of the Antisecretory Response to Estrogen in Rat Distal Colon throughout the Estrous Cycle

“…It is possible that the regulation of Cl Ϫ secretion by estrogen in the distal colon and the components of the molecular mechanism involved may vary depending on the hormonal background of the female. Cl Ϫ secretion in the distal colon can be up-regulated by two distinct mechanisms: an increase in intracellular Ca 2ϩ (12) or cAMP activity (13). Cl Ϫ enters the cell across the basolateral membrane by cotransport with K ϩ and Na ϩ .…”