title: Regulation of Cl- secretion by alpha2-adrenergic receptors in mouse colonic epithelium.
abstract: Previous studies have shown that alpha2 adrenoceptor (alpha2AR) agonists inhibit electrolyte secretion in colonic epithelia, but little is known about the molecular mechanisms involved in this process. In this study we examined the effect of alpha2AR activation on transepithelial anion secretion across isolated murine colonic epithelium. We found that alpha2AR agonists, UK 14,304, clonidine and medetomidine were potent inhibitors of anion secretion, especially in the proximal colon. Short circuit current measurements (Isc) in colonic epithelia from normal and cystic fibrosis (CF) mice showed that alpha2AR agonists inhibited basal cystic fibrosis transmembrane conductance regulator (CFTR)-mediated Cl- secretion but had no effect on CFTR activation by cAMP-dependent phosphorylation. Apical administration of an ionophore, nystatin (90 microg ml-1), was used to investigate the effect of UK 14,304 on basolateral K+ transport. The Na+-K+-ATPase current, measured as ouabain-sensitive current in the absence of ion gradients, was unaltered by pretreatment of the tissue with UK 14,304 (1 microM). In the presence of a basolaterally directed K+ gradient, UK 14,304 significantly reduced nystatin-activated Isc indicating that activation of alpha2ARs inhibits basolateral K+ channels. Studies with selective K+ channel inhibitors and openers showed that alpha2AR agonists inhibited KATP channels that were tonically active in mouse colonic epithelia. RT-PCR and pharmacological studies suggested that these channels could be similar to vascular smooth muscle KATP channels comprising Kir6.1/SUR2B or Kir6.2/SUR2B subunits. Inhibition of anion secretion by alpha2AR agonists required activation of pertussis toxin-sensitive Gi/o proteins, but did not involve classical second messengers, such as cAMP or Ca2+. In summary, alpha2ARs inhibit anion secretion in colonic epithelia by acting on basolateral KATP channels, through a process that does not involve classical second messengers.
authors.affiliation: Department of Physiology, University of Alberta, Edmonton, Canada T6G 2H7.
authors.forename: Rebecca S
authors.initials: RS
authors.lastname: Lam
authors.forename: Ernst M
authors.initials: EM
authors.lastname: App
authors.forename: Drew
authors.initials: D
authors.lastname: Nahirney
authors.forename: Artur J
authors.initials: AJ
authors.lastname: Szkotak
authors.forename: Maria A
authors.initials: MA
authors.lastname: Vieira-Coelho
authors.forename: Malcolm
authors.initials: M
authors.lastname: King
authors.forename: Marek
authors.initials: M
authors.lastname: Duszyk
mesh_terms: D018528:ATP-Binding Cassette Transporters; D000818:Animals; D000068438:Brimonidine Tartrate; D002118:Calcium / Q000502:physiology; D002712:Chlorides / Q000378:metabolism*; D002851:Chromatography, High Pressure Liquid; D003106:Colon / Q000378:metabolism*; D000242:Cyclic AMP / Q000502:physiology; D003550:Cystic Fibrosis / Q000378:metabolism; D019005:Cystic Fibrosis Transmembrane Conductance Regulator / Q000037:antagonists & inhibitors / Q000378:metabolism; D004847:Epithelial Cells / Q000378:metabolism; D019204:GTP-Binding Proteins / Q000378:metabolism; D066298:In Vitro Techniques; D007413:Intestinal Mucosa / Q000378:metabolism*; D007473:Ion Channels / Q000378:metabolism; D054086:KATP Channels; D051379:Mice; D008807:Mice, Inbred BALB C; D008810:Mice, Inbred C57BL; D009638:Norepinephrine / Q000378:metabolism; D015221:Potassium Channels / Q000378:metabolism; D024661:Potassium Channels, Inwardly Rectifying; D011810:Quinoxalines / Q000494:pharmacology; D011863:Radioimmunoassay; D018341:Receptors, Adrenergic, alpha-2 / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction
chemical_list: D018528:ATP-Binding Cassette Transporters; D002712:Chlorides; D007473:Ion Channels; D054086:KATP Channels; D015221:Potassium Channels; D024661:Potassium Channels, Inwardly Rectifying; D011810:Quinoxalines; D018341:Receptors, Adrenergic, alpha-2; C092520:uK-ATP-1 potassium channel; D019005:Cystic Fibrosis Transmembrane Conductance Regulator; D000068438:Brimonidine Tartrate; D000242:Cyclic AMP; D019204:GTP-Binding Proteins; D002118:Calcium; D009638:Norepinephrine