title: Bending the primary cilium opens Ca2+-sensitive intermediate-conductance K+ channels in MDCK cells.
abstract: Increasing tubular fluid flow rate has previously been shown to induce K+ secretion in mammalian cortical collecting duct. The mechanism responsible was examined in the present study using MDCK cells as a model. The change in membrane potential difference (EM) of MDCK cells was measured with a fluorescent voltage-sensitive dye, DiBAC4(3), when the cell's primary cilium was continuously bent with a micropipette or by the flow of perfusate. Bending the cilium produced a hyperpolarization of the membrane that lagged behind the increase in intracellular Ca2+ concentration by an average of 36 seconds. Gd3+, an inhibitor of the flow-induced Ca2+ increase, prevented the hyperpolarization. Blocking K+ channels with Ba2+ reduced the flow-induced hyperpolarization, implying that it resulted from activation of Ca2+-sensitive K+ channels. Further studies demonstrated that the hyperpolarization was diminished by the blocker of Ca2+-activated K+ channels, charybdotoxin, whereas iberiotoxin or apamin had no effect, results consistent with the activation of intermediate-conductance Ca2+-sensitive K+ channels. RT-PCR analysis and sequencing confirmed the presence of intermediate-conductance K+ channels in MDCK cells. We conclude that the increase in intracellular Ca2+ associated with bending of the primary cilium is the cause of the hyperpolarization and increased K+ conductance in MDCK cells.
authors.affiliation: The Water and Salt Research Center, University of Aarhus, Aarhus, Denmark. helle.praetorius@iekf.au.dk
authors.forename: H A
authors.initials: HA
authors.lastname: Praetorius
authors.forename: J
authors.initials: J
authors.lastname: Frokiaer
authors.forename: S
authors.initials: S
authors.lastname: Nielsen
authors.forename: K R
authors.initials: KR
authors.lastname: Spring
mesh_terms: D000818:Animals; D002460:Cell Line; D002923:Cilia / Q000187:drug effects / Q000502:physiology* / Q000648:ultrastructure; D004285:Dogs; D004553:Electric Conductivity; D005682:Gadolinium / Q000494:pharmacology; D015640:Ion Channel Gating / Q000187:drug effects / Q000502:physiology*; D007668:Kidney / Q000502:physiology* / Q000648:ultrastructure; D040542:Mechanotransduction, Cellular / Q000502:physiology*; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D009038:Motion; D010812:Physical Stimulation / Q000379:methods; D011188:Potassium / Q000502:physiology; D024681:Potassium Channels, Calcium-Activated / Q000187:drug effects / Q000502:physiology*
chemical_list: D024681:Potassium Channels, Calcium-Activated; D005682:Gadolinium; D011188:Potassium