title: Identification and functional characterization of the intermediate-conductance Ca(2+)-activated K(+) channel (IK-1) in biliary epithelium.
abstract: In the liver, adenosine triphosphate (ATP) is an extracellular signaling molecule that is released into bile and stimulates a biliary epithelial cell secretory response via engagement of apical P2 receptors. The molecular identities of the ion channels involved in ATP-mediated secretory responses have not been fully identified. Intermediate-conductance Ca(2+)-activated K(+) channels (IK) have been identified in biliary epithelium, but functional data are lacking. The aim of these studies therefore was to determine the location, function, and regulation of IK channels in biliary epithelial cells and to determine their potential contribution to ATP-stimulated secretion. Expression of IK-1 mRNA was found in both human Mz-Cha-1 biliary cells and polarized normal rat cholangiocyte (NRC) monolayers, and immunostaining revealed membrane localization with a predominant basolateral signal. In single Mz-Cha-1 cells, exposure to ATP activated K(+) currents, increasing current density from 1.6 +/- 0.1 to 7.6 +/- 0.8 pA/pF. Currents were dependent on intracellular Ca(2+) and sensitive to clotrimazole and TRAM-34 (specific IK channel inhibitors). Single-channel recording demonstrated that clotrimazole-sensitive K(+) currents had a unitary conductance of 46.2 +/- 1.5 pS, consistent with IK channels. In separate studies, 1-EBIO (an IK activator) stimulated K(+) currents in single cells that were inhibited by clotrimazole. In polarized NRC monolayers, ATP significantly increased transepithelial secretion which was inhibited by clotrimazole. Lastly, ATP-stimulated K(+) currents were inhibited by the P2Y receptor antagonist suramin and by the inositol 1,4,5-triphosphate (IP3) receptor inhibitor 2-APB. Together these studies demonstrate that IK channels are present in biliary epithelial cells and contribute to ATP-stimulated secretion through a P2Y-IP3 receptor pathway.
authors.affiliation: Department of Pediatrics, University of Texas Southwestern Medical Center, Dallas, Texas, USA.
authors.forename: Amal K
authors.initials: AK
authors.lastname: Dutta
authors.forename: Al-karim
authors.initials: AK
authors.lastname: Khimji
authors.forename: Meghana
authors.initials: M
authors.lastname: Sathe
authors.forename: Charles
authors.initials: C
authors.lastname: Kresge
authors.forename: Vinay
authors.initials: V
authors.lastname: Parameswara
authors.forename: Victoria
authors.initials: V
authors.lastname: Esser
authors.forename: Don C
authors.initials: DC
authors.lastname: Rockey
authors.forename: Andrew P
authors.initials: AP
authors.lastname: Feranchak
mesh_terms: D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D001030:Apamin / Q000494:pharmacology; D001464:Barium / Q000494:pharmacology; D001562:Benzimidazoles / Q000494:pharmacology; D001659:Biliary Tract / Q000166:cytology / Q000502:physiology*; D002021:Buffers; D045744:Cell Line, Tumor; D002462:Cell Membrane / Q000378:metabolism; D002478:Cells, Cultured; D002614:Chelating Agents / Q000494:pharmacology; D003022:Clotrimazole / Q000494:pharmacology; D004533:Egtazic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D055724:Electrophysiological Phenomena; D004847:Epithelial Cells / Q000187:drug effects / Q000502:physiology*; D015870:Gene Expression / Q000235:genetics; D006801:Humans; D053496:Inositol 1,4,5-Trisphosphate Receptors / Q000037:antagonists & inhibitors; D051660:Intermediate-Conductance Calcium-Activated Potassium Channels / Q000819:agonists / Q000037:antagonists & inhibitors / Q000502:physiology*; D008954:Models, Biological; D018408:Patch-Clamp Techniques; D058919:Purinergic P2 Receptor Antagonists; D011720:Pyrazoles / Q000494:pharmacology; D051381:Rats; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology; D013498:Suramin / Q000494:pharmacology
chemical_list: D001562:Benzimidazoles; D002021:Buffers; D002614:Chelating Agents; D053496:Inositol 1,4,5-Trisphosphate Receptors; D051660:Intermediate-Conductance Calcium-Activated Potassium Channels; C496923:KCNN4 protein, human; C491575:Kcnn4 protein, rat; D058919:Purinergic P2 Receptor Antagonists; D011720:Pyrazoles; C411671:TRAM 34; C070379:1,2-bis(2-aminophenoxy)ethane N,N,N',N'-tetraacetic acid acetoxymethyl ester; D001030:Apamin; D001464:Barium; D004533:Egtazic Acid; D013498:Suramin; D000255:Adenosine Triphosphate; D003022:Clotrimazole; C102635:1-ethyl-2-benzimidazolinone