Emerging role of the calcium-activated, small conductance, SK3 K + channel in distal tubule function: Regulation by TRPV4

Jonathan Berrout, Mykola Mamenko, Oleg L. Zaika, Lihe Chen, Wenzheng Zang, Oleh Pochynyuk, Roger G. O'Neil

Research output: Contribution to journalArticle

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Abstract

The Ca2+-activated, maxi-K (BK) K+ channel, with low Ca2+-binding affinity, is expressed in the distal tubule of the nephron and contributes to flow-dependent K+ secretion. In the present study we demonstrate that the Ca2+-activated, SK3 (KCa2.3) K + channel, with high Ca2+-binding affinity, is also expressed in the mouse kidney (RT-PCR, immunoblots). Immunohistochemical evaluations using tubule specific markers demonstrate significant expression of SK3 in the distal tubule and the entire collecting duct system, including the connecting tubule (CNT) and cortical collecting duct (CCD). In CNT and CCD, main sites for K+ secretion, the highest levels of expression were along the apical (luminal) cell membranes, including for both principal cells (PCs) and intercalated cells (ICs), posturing the channel for Ca2+- dependent K+ secretion. Fluorescent assessment of cell membrane potential in native, split-opened CCD, demonstrated that selective activation of the Ca2+-permeable TRPV4 channel, thereby inducing Ca2+ influx and elevating intracellular Ca2+ levels, activated both the SK3 channel and the BK channel leading to hyperpolarization of the cell membrane. The hyperpolarization response was decreased to a similar extent by either inhibition of SK3 channel with the selective SK antagonist, apamin, or by inhibition of the BK channel with the selective antagonist, iberiotoxin (IbTX). Addition of both inhibitors produced a further depolarization, indicating cooperative effects of the two channels on Vm. It is concluded that SK3 is functionally expressed in the distal nephron and collecting ducts where induction of TRPV4-mediated Ca2+ influx, leading to elevated intracellular Ca2+ levels, activates this high Ca2+- affinity K+ channel. Further, with sites of expression localized to the apical cell membrane, especially in the CNT and CCD, SK3 is poised to be a key pathway for Ca2+-dependent regulation of membrane potential and K+ secretion.

Original languageEnglish (US)
Article numbere95149
JournalPloS one
Volume9
Issue number4
DOIs
StatePublished - Apr 24 2014

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potassium channels
Large-Conductance Calcium-Activated Potassium Channels
Ducts
Cell Membrane
Cell membranes
Calcium
calcium
Nephrons
Membrane Potentials
Apamin
cell membranes
secretion
nephrons
Depolarization
Kidney
membrane potential
Polymerase Chain Reaction
antagonists
Chemical activation
Membranes

ASJC Scopus subject areas

  • Biochemistry, Genetics and Molecular Biology(all)
  • Agricultural and Biological Sciences(all)

Cite this

Emerging role of the calcium-activated, small conductance, SK3 K + channel in distal tubule function : Regulation by TRPV4. / Berrout, Jonathan; Mamenko, Mykola; Zaika, Oleg L.; Chen, Lihe; Zang, Wenzheng; Pochynyuk, Oleh; O'Neil, Roger G.

In: PloS one, Vol. 9, No. 4, e95149, 24.04.2014.

Research output: Contribution to journalArticle

Berrout, Jonathan ; Mamenko, Mykola ; Zaika, Oleg L. ; Chen, Lihe ; Zang, Wenzheng ; Pochynyuk, Oleh ; O'Neil, Roger G. / Emerging role of the calcium-activated, small conductance, SK3 K + channel in distal tubule function : Regulation by TRPV4. In: PloS one. 2014 ; Vol. 9, No. 4.
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abstract = "The Ca2+-activated, maxi-K (BK) K+ channel, with low Ca2+-binding affinity, is expressed in the distal tubule of the nephron and contributes to flow-dependent K+ secretion. In the present study we demonstrate that the Ca2+-activated, SK3 (KCa2.3) K + channel, with high Ca2+-binding affinity, is also expressed in the mouse kidney (RT-PCR, immunoblots). Immunohistochemical evaluations using tubule specific markers demonstrate significant expression of SK3 in the distal tubule and the entire collecting duct system, including the connecting tubule (CNT) and cortical collecting duct (CCD). In CNT and CCD, main sites for K+ secretion, the highest levels of expression were along the apical (luminal) cell membranes, including for both principal cells (PCs) and intercalated cells (ICs), posturing the channel for Ca2+- dependent K+ secretion. Fluorescent assessment of cell membrane potential in native, split-opened CCD, demonstrated that selective activation of the Ca2+-permeable TRPV4 channel, thereby inducing Ca2+ influx and elevating intracellular Ca2+ levels, activated both the SK3 channel and the BK channel leading to hyperpolarization of the cell membrane. The hyperpolarization response was decreased to a similar extent by either inhibition of SK3 channel with the selective SK antagonist, apamin, or by inhibition of the BK channel with the selective antagonist, iberiotoxin (IbTX). Addition of both inhibitors produced a further depolarization, indicating cooperative effects of the two channels on Vm. It is concluded that SK3 is functionally expressed in the distal nephron and collecting ducts where induction of TRPV4-mediated Ca2+ influx, leading to elevated intracellular Ca2+ levels, activates this high Ca2+- affinity K+ channel. Further, with sites of expression localized to the apical cell membrane, especially in the CNT and CCD, SK3 is poised to be a key pathway for Ca2+-dependent regulation of membrane potential and K+ secretion.",
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