title: Lovastatin-Induced Phosphatidylinositol-4-Phosphate 5-Kinase Diffusion from Microvilli Stimulates ROMK Channels.
abstract: We recently showed that lovastatin attenuates cyclosporin A (CsA)-induced damage of cortical collecting duct (CCD) principal cells by reducing intracellular cholesterol. Previous studies showed that, in cell expression models or artificial membranes, exogenous cholesterol directly inhibits inward rectifier potassium channels, including Kir1.1 (Kcnj1; the gene locus for renal outer medullary K(+) [ROMK1] channels). Therefore, we hypothesized that lovastatin might stimulate ROMK1 by reducing cholesterol in CCD cells. Western blots showed that mpkCCDc14 cells express ROMK1 channels with molecular masses that approximate the molecular masses of ROMK1 in renal tubules detected before and after treatment with DTT. Confocal microscopy showed that ROMK1 channels were not in the microvilli, where cholesterol-rich lipid rafts are located, but rather, the planar regions of the apical membrane of mpkCCDc14 cells. Furthermore, phosphatidylinositol-4,5-bisphosphate [PI(4,5)P2], an activator of ROMK channels, was detected mainly in the microvilli under resting conditions along with the kinase responsible for PI(4,5)P2 synthesis, phosphatidylinositol-4-phosphate 5-kinase, type I γ [PI(4)P5K I γ], which may explain the low basal open probability and increased sensitivity to tetraethylammonium observed here for this channel. Notably, lovastatin induced PI(4)P5K I γ diffusion into planar regions and elevated PI(4,5)P2 and ROMK1 open probability in these regions through a cholesterol-associated mechanism. However, exogenous cholesterol alone did not induce these effects. These results suggest that lovastatin stimulates ROMK1 channels, at least in part, by inducing PI(4,5)P2 synthesis in planar regions of the renal CCD cell apical membrane, suggesting that lovastatin could reduce cyclosporin-induced nephropathy and associated hyperkalemia.
authors.affiliation: Departments of Radiology and Cardiology, Fourth Hospital of Harbin Medical University, Harbin, Heilongjiang, China; Department of Physiology and.
authors.forename: Bing-Chen
authors.initials: BC
authors.lastname: Liu
authors.affiliation: Departments of Radiology and Department of Physiology and Molecular Imaging Center, Harbin Medical University, Harbin, Heilongjiang, China; and.
authors.forename: Li-Li
authors.initials: LL
authors.lastname: Yang
authors.affiliation: Departments of Radiology and Cardiology, Fourth Hospital of Harbin Medical University, Harbin, Heilongjiang, China; Department of Physiology and.
authors.forename: Xiao-Yu
authors.initials: XY
authors.lastname: Lu
authors.affiliation: Cardiology, Fourth Hospital of Harbin Medical University, Harbin, Heilongjiang, China; Department of Physiology and.
authors.forename: Xiang
authors.initials: X
authors.lastname: Song
authors.affiliation: Department of Physiology and.
authors.forename: Xue-Chen
authors.initials: XC
authors.lastname: Li
authors.affiliation: Department of Physiology and.
authors.forename: Guangping
authors.initials: G
authors.lastname: Chen
authors.affiliation: Department of Biomedical Engineering, University of Alabama at Birmingham, Birmingham, Alabama;
authors.forename: Yichao
authors.initials: Y
authors.lastname: Li
authors.affiliation: Department of Biomedical Engineering, University of Alabama at Birmingham, Birmingham, Alabama;
authors.forename: Xincheng
authors.initials: X
authors.lastname: Yao
authors.affiliation: Department of Physiology and.
authors.forename: Donald R
authors.initials: DR
authors.lastname: Humphrey
authors.affiliation: Department of Physiology and Center for Cell and Molecular Signaling, Emory University School of Medicine, Atlanta, Georgia.
authors.forename: Douglas C
authors.initials: DC
authors.lastname: Eaton
authors.affiliation: Departments of Radiology and Molecular Imaging Center, Harbin Medical University, Harbin, Heilongjiang, China; and shenbzh@vip.sina.com heping.ma@emory.edu.
authors.forename: Bao-Zhong
authors.initials: BZ
authors.lastname: Shen
authors.affiliation: Department of Physiology and Center for Cell and Molecular Signaling, Emory University School of Medicine, Atlanta, Georgia shenbzh@vip.sina.com heping.ma@emory.edu.
authors.forename: He-Ping
authors.initials: HP
authors.lastname: Ma
mesh_terms: D000704:Analysis of Variance; D000818:Animals; D015153:Blotting, Western; D002462:Cell Membrane / Q000378:metabolism; D002478:Cells, Cultured; D002784:Cholesterol / Q000378:metabolism*; D003524:Cyclosporins / Q000378:metabolism; D005786:Gene Expression Regulation; D007685:Kidney Tubules, Collecting / Q000187:drug effects / Q000378:metabolism*; D008148:Lovastatin / Q000494:pharmacology*; D051379:Mice; D018613:Microscopy, Confocal; D008871:Microvilli / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure; D023421:Models, Animal; D024661:Potassium Channels, Inwardly Rectifying / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D034741:RNA, Small Interfering / Q000378:metabolism; D060888:Real-Time Polymerase Chain Reaction / Q000379:methods; D012016:Reference Values; D012680:Sensitivity and Specificity; D015398:Signal Transduction
chemical_list: D003524:Cyclosporins; C510693:Kcnj1 protein, mouse; D024661:Potassium Channels, Inwardly Rectifying; D034741:RNA, Small Interfering; D002784:Cholesterol; D008148:Lovastatin
keywords: K channels; cyclosporin; signaling; statins; tubule cells