ABSTRACT
Mutations in either Pkd1 or Pkd2 result in Autosomal Dominant Polycystic Kidney Disease (ADPKD). Although PKD2 is proposed to be an ion channel subunit, recordings of PKD2 ion channels conflict in their properties. Using a new ADPKD mouse model, we observe primary cilia are abnormally long in cells associated with cysts. Using primary cultures of collecting duct epithelial cells, we show that PKD2, but not PKD1, is a required subunit for primary cilia ion channel. The ciliary PKD2 channel conducts potassium and sodium ions, but little calcium. We also demonstrate that PKD2 is not constitutively active in the plasma membrane, but PKD2 channels are functional in primary cilia and are sensitized by high cilioplasmic [Ca2+]. We introduce a novel method for measuring PKD2 channels heterologously expressed in primary cilia of HEK-293 cells, which will have utility characterizing Pkd2 variants that cause ADPKD in their native ciliary membrane.
Footnotes
- Abbreviations used
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- Pkd1 or Pkd2 (lower case letters): when referring to polycystin genes
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- PKD1 or PKD2 (capital letters): when referring to polycystin proteins
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- cPkd1: a mouse expressing Pax8rtTA; TetO-cre; Pkd1fl/fl
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- cPkd2: a mouse expressing Pax8rtTA; TetO-cre; Pkd2fl/fl
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- Arl13B-EGFPtg: a transgenic mouse expressing multiple copies of the cilia-localized Arl13B-EGFP gene
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- pIMCD: primary distal collecting duct tubule epithelial cells isolated from mice used in the study (Arl13B-EGFPtg; Arl13B-EGFPtg:cPkd1; Arl13B-EGFPtg:cPkd2)
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- [free-Ca2+]in: internal free calcium concentration (cilioplasm or cytoplasm)