Bending the primary cilium opens Ca2+-sensitive intermediate-conductance K+ channels in MDCK cells

• Published in: The Journal of membrane biology 2003-02, Vol.191 (3), p.193-200
• Main Authors: Praetorius, H A, Frokiaer, J, Nielsen, S, Spring, K R
• Format: Article
• Language: English
• Subjects: Animals; Cell Line; Cilia - drug effects; Cilia - physiology; Cilia - ultrastructure; Dogs; Electric Conductivity; Gadolinium - pharmacology; Ion Channel Gating - drug effects; Ion Channel Gating - physiology; Kidney - physiology; Kidney - ultrastructure; Mechanotransduction, Cellular - physiology; Membrane Potentials - drug effects; Membrane Potentials - physiology; Motion; Physical Stimulation - methods; Potassium - physiology; Potassium Channels, Calcium-Activated - drug effects; Potassium Channels, Calcium-Activated - physiology
• ISSN: 0022-2631; 1432-1424
• DOI: 10.1007/s00232-002-1055-z

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.