Identification and functional characterization of the intermediate- conductance Ca2+-activated K+ channel (IK-1) in biliary epithelium

Amal K. Dutta, Al Karim Khimji, Meghana Sathe, Charles Kresge, Vinay Parameswara, Victoria Esser, Don C. Rockey, Andrew P. Feranchak

Research output: Contribution to journalArticle

22 Citations (Scopus)

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 Ca2+-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 Ca2+ 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.

Original languageEnglish (US)
JournalAmerican Journal of Physiology - Gastrointestinal and Liver Physiology
Volume297
Issue number5
DOIs
StatePublished - Nov 2009

Fingerprint

Calcium-Activated Potassium Channels
Epithelium
Clotrimazole
Adenosine Triphosphate
Inositol 1,4,5-Trisphosphate Receptors
Epithelial Cells
Suramin
Inositol 1,4,5-Trisphosphate
Ion Channels
Bile
Messenger RNA
Membranes
Liver

Keywords

  • ATP
  • Bile formation
  • KCa channel
  • Liver
  • P2Y receptor
  • Purinergic

ASJC Scopus subject areas

  • Gastroenterology
  • Physiology (medical)
  • Physiology
  • Hepatology

Cite this

Identification and functional characterization of the intermediate- conductance Ca2+-activated K+ channel (IK-1) in biliary epithelium. / Dutta, Amal K.; Khimji, Al Karim; Sathe, Meghana; Kresge, Charles; Parameswara, Vinay; Esser, Victoria; Rockey, Don C.; Feranchak, Andrew P.

In: American Journal of Physiology - Gastrointestinal and Liver Physiology, Vol. 297, No. 5, 11.2009.

Research output: Contribution to journalArticle

Dutta, Amal K. ; Khimji, Al Karim ; Sathe, Meghana ; Kresge, Charles ; Parameswara, Vinay ; Esser, Victoria ; Rockey, Don C. ; Feranchak, Andrew P. / Identification and functional characterization of the intermediate- conductance Ca2+-activated K+ channel (IK-1) in biliary epithelium. In: American Journal of Physiology - Gastrointestinal and Liver Physiology. 2009 ; Vol. 297, No. 5.
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AU - Dutta, Amal K.

AU - Khimji, Al Karim

AU - Sathe, Meghana

AU - Kresge, Charles

AU - Parameswara, Vinay

AU - Esser, Victoria

AU - Rockey, Don C.

AU - Feranchak, Andrew P.

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N2 - 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 Ca2+-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 Ca2+ 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.

AB - 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 Ca2+-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 Ca2+ 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.

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KW - P2Y receptor

KW - Purinergic

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