K⁺ channel K_VLQT1 located in the basolateral membrane of distal colonic epithelium is not essential for activating Cl⁻ secretion

Abstract

The cellular mechanism for Cl(-) and K(+) secretion in the colonic epithelium requires K(+) channels in the basolateral and apical membranes. Colonic mucosa from guinea pig and rat were fixed, sectioned, and then probed with antibodies to the K(+) channel proteins K(V)LQT1 (Kcnq1) and minK-related peptide 2 (MiRP2, Kcne3). Immunofluorescence labeling for Kcnq1 was most prominent in the lateral membrane of crypt cells in rat colon. The guinea pig distal colon had distinct lateral membrane immunoreactivity for Kcnq1 in crypt and surface cells. In addition, Kcne3, an auxiliary subunit for Kcnq1, was detected in the lateral membrane of crypt and surface cells in guinea pig distal colon. Transepithelial short-circuit current (I(sc)) and transepithelial conductance (G(t)) were measured for colonic mucosa during secretory activation by epinephrine (EPI), prostaglandin E(2) (PGE(2)), and carbachol (CCh). HMR1556 (10 microM), an inhibitor of Kcnq1 channels (Gerlach U, Brendel J, Lang HJ, Paulus EF, Weidmann K, Brüggemann A, Busch A, Suessbrich H, Bleich M, and Greger R. J Med Chem 44: 3831-3837, 2001), partially (approximately 50%) inhibited Cl(-) secretory I(sc) and G(t) activated by PGE(2) and CCh in rat colon with an IC(50) of 55 nM, but in guinea pig distal colon Cl(-) secretory I(sc) and G(t) were unaltered. EPI-activated K(+)-secretory I(sc) and G(t) also were essentially unaltered by HMR1556 in both rat and guinea pig colon. Although immunofluorescence labeling with a Kcnq1 antibody supported the basolateral membrane presence in colonic epithelium of the guinea pig as well as the rat, the Kcnq1 K(+) channel is not an essential component for producing Cl(-) secretion. Other K(+) channels present in the basolateral membrane presumably must also contribute directly to the K(+) conductance necessary for K(+) exit during activation of Cl(-) secretion in the colonic mucosa.

Protein distribution of Kcnq1, Kcnh2, and Kcne3 potassium channel subunits during mouse embryonic development

“…Previous studies in the adult digestive tract have provided evidence of Kcnq1 expression in the parietal cells of the stomach (Dedek and Waldegger, 2001) as well as in crypt cells of the colon and small intestine (Bleich and Warth, 2000). A putative role in potassium conductance-mediated acid and/or chloride secretion of Kcnq1 in these cells have been proposed (Liao et al, 2005). Our data support that potassium conductance in the epithelial lining of the digestive tract seems to be established at an early stage of development.…”

Segregation of Na/H exchanger-3 and Cl/HCO3exchanger SLC26A3 (DRA) in rodent cecum and colon

“…The functional segments demarcated by our study appear to have two easily identifiable anatomical features. First, the proximal portion of the colon that expresses abundant NHE3 but scant DRA (0 -20% length) roughly corresponds to the segment that displays serosal palmleaf striations (21,31,55). Second, the portion of the rodent distal colon that is deficient in NHE3 (60 -100% colon length in rats and 75-100% in mice) is largely comprised of the extraperitoneal segment that extends from the pelvic brim to the anus; previous studies have indicated that this segment, sometimes called the rectum (30), uniquely exhibits aldosterone-stimulated electrogenic Na ϩ absorption and a weaker Cl Ϫ secretory capacity (7,30,43).…”

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

“…Primers for Y2-NpR were (forward primer) 5Ј-aaa tgg gtc ctg tcc tct gcc-3Ј(353-373) and (reverse primer) 5Ј-tgc ctc cgc tgg tgg tag tgg-3Ј(774-794). Proteins were isolated from colonic mucosa as described previously (33,52). Briefly, after disruption by sonication in a buffered solution containing protease inhibitors, epithelial cell lysates were centrifuged to obtain a membrane sample.…”

“…Colonic tissues were fixed after isolation, as described previously (33,52). Briefly, isolated mucosal sheets were chemically fixed followed by dehydration, sectioning, and mounting on gelatin-coated slides.…”

“…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.…”