title: Na(+)/Ca(2+) exchange regulates Ca(2+)-dependent duodenal mucosal ion transport and HCO(3)(-) secretion in mice.
abstract: Stimulation of muscarinic receptors in duodenal mucosa raises intracellular Ca(2+), which regulates ion transport, including HCO(3)(-) secretion. However, the underlying Ca(2+) handling mechanisms are poorly understood. The aim of the present study was to determine whether Na(+)/Ca(2+) exchanger (NCX) plays a role in the regulation of duodenal mucosal ion transport and HCO(3)(-) secretion by controlling Ca(2+) homeostasis. Mouse duodenal mucosa was mounted in Ussing chambers. Net ion transport was assessed as short-circuit current (I(sc)), and HCO(3)(-) secretion was determined by pH-stat. Expression of NCX in duodenal mucosae was analyzed by Western blot, and cytosolic Ca(2+) in duodenocytes was measured by fura 2. Carbachol (100 muM) increased I(sc) in a biphasic manner: an initial transient peak within 2 min and a later sustained plateau starting at 10 min. Carbachol-induced HCO(3)(-) secretion peaked at 10 min. 2-Aminoethoxydiphenylborate (2-APB, 100 muM) or LiCl (30 mM) significantly reduced the initial peak in I(sc) by 51 or 47%, respectively, and abolished the plateau phase of I(sc) without affecting HCO(3)(-) secretion induced by carbachol. Ryanodine (100 muM), caffeine (10 mM), and nifedipine (10 muM) had no effect on either response to carbachol. In contrast, nickel (5 mM) and KB-R7943 (10-30 muM) significantly inhibited carbachol-induced increases in duodenal mucosal I(sc) and HCO(3)(-) secretion. Western blot analysis showed expression of NCX1 proteins in duodenal mucosae, and functional NCX in duodenocytes was demonstrated in Ca(2+) imaging experiments where Na(+) depletion elicited Ca(2+) entry via the reversed mode of NCX. These results indicate that NCX contributes to the regulation of Ca(2+)-dependent duodenal mucosal ion transport and HCO(3)(-) secretion that results from stimulation of muscarinic receptors.
authors.affiliation: Division of Gastroenterology, Department of Medicine, UCSD Medical Center 8414, 200 West Arbor Drive, San Diego, CA 92103, USA. h2dong@ucsd.edu
authors.forename: Hui
authors.initials: H
authors.lastname: Dong
authors.forename: Zachary M
authors.initials: ZM
authors.lastname: Sellers
authors.forename: Anders
authors.initials: A
authors.lastname: Smith
authors.forename: Jimmy Y C
authors.initials: JY
authors.lastname: Chow
authors.forename: Kim E
authors.initials: KE
authors.lastname: Barrett
mesh_terms: D000818:Animals; D001639:Bicarbonates / Q000378:metabolism*; D001693:Biological Transport, Active; D015153:Blotting, Western; D002118:Calcium / Q000502:physiology*; D002217:Carbachol / Q000494:pharmacology; D015194:Diffusion Chambers, Culture; D004386:Duodenum / Q000378:metabolism*; D004847:Epithelial Cells / Q000378:metabolism; D066298:In Vitro Techniques; D007413:Intestinal Mucosa / Q000378:metabolism*; D018021:Lithium Chloride / Q000494:pharmacology; D051379:Mice; D018721:Muscarinic Agonists / Q000494:pharmacology; D012964:Sodium / Q000378:metabolism; D019831:Sodium-Calcium Exchanger / Q000037:antagonists & inhibitors / Q000378:metabolism*; D013890:Thiourea / Q000031:analogs & derivatives* / Q000494:pharmacology
chemical_list: C101670:2-(2-(4-(4-nitrobenzyloxy)phenyl)ethyl)isothiourea methanesulfonate; D001639:Bicarbonates; D018721:Muscarinic Agonists; D019831:Sodium-Calcium Exchanger; D002217:Carbachol; D012964:Sodium; D018021:Lithium Chloride; D013890:Thiourea; D002118:Calcium