Heightened epithelial Na+ channel-mediated Na+ absorption in a murine polycystic kidney disease model epithelium lacking apical monocilia.
The Tg737 degrees (rpk) autosomal recessive polycystic kidney disease (ARPKD) mouse carries a hypomorphic mutation in the Tg737 gene. Because of the absence of its protein product Polaris, the nonmotile primary monocilium central to the luminal membrane of ductal epithelia, such as the cortical collecting duct (CCD) principal cell (PC), is malformed. Although the functions of the renal monocilium remain elusive, primary monocilia or flagella on neurons act as sensory organelles. Thus we hypothesized that the PC monocilium functions as a cellular sensor. To test this hypothesis, we assessed the contribution of Polaris and cilium structure and function to renal epithelial ion transport electrophysiology. Properties of Tg737 degrees (rpk) mutant CCD PC clones were compared with clones genetically rescued with wild-type Tg737 cDNA. All cells were grown as polarized cell monolayers with similarly high transepithelial resistance on permeable filter supports. Three- to fourfold elevated transepithelial voltage (V(te)) and short-circuit current (I(sc)) were measured in mutant orpk monolayers vs. rescued controls. Pharmacological and cell biological examination of this enhanced electrical end point in mutant monolayers revealed that epithelial Na(+) channels (ENaCs) were upregulated. Amiloride, ENaC-selective amiloride analogs (benzamil and phenamil), and protease inhibitors (aprotinin and leupeptin) attenuated heightened V(te) and I(sc). Higher concentrations of additional amiloride analogs (ethylisopropylamiloride and dimethylamiloride) also revealed inhibition of V(te). Cell culture requirements and manipulations were also consistent with heightened ENaC expression and function. Together, these data suggest that ENaC expression and/or function are upregulated in the luminal membrane of mutant, cilium-deficient orpk CCD PC monolayers vs. cilium-competent controls. When the genetic lesion causes loss or malformation of the monocilium, ENaC-driven Na(+) hyperabsorption may explain the rapid emergence of severe hypertension in a majority of patients with ARPKD.
Olteanu
Dragos
D
Department of Physiology, Univ. of Alabama at Birmingham, MCLM 740, 1918 University Blvd., 35294-0005, USA.
Yoder
Bradley K
BK
Liu
Wen
W
Croyle
Mandy J
MJ
Welty
Elisabeth A
EA
Rosborough
Kelley
K
Wyss
J Michael
JM
Bell
P Darwin
PD
Guay-Woodford
Lisa M
LM
Bevensee
Mark O
MO
Satlin
Lisa M
LM
Schwiebert
Erik M
EM
D000584:Amiloride / Q000031:analogs & derivatives / Q000378:metabolism; D000818:Animals; D002478:Cells, Cultured; D002923:Cilia / Q000378:metabolism*; D004195:Disease Models, Animal; D004594:Electrophysiology; D004847:Epithelial Cells / Q000166:cytology / Q000378:metabolism; D053503:Epithelial Sodium Channels; D007668:Kidney / Q000166:cytology / Q000378:metabolism; D051379:Mice; D010447:Peptide Hydrolases / Q000378:metabolism; D017044:Polycystic Kidney, Autosomal Recessive / Q000235:genetics / Q000378:metabolism*; D012964:Sodium / Q000378:metabolism*; D026941:Sodium Channel Blockers / Q000378:metabolism; D015222:Sodium Channels / Q000235:genetics / Q000378:metabolism*; D025521:Tumor Suppressor Proteins / Q000235:genetics / Q000378:metabolism
D053503:Epithelial Sodium Channels; D026941:Sodium Channel Blockers; D015222:Sodium Channels; C490898:Tg737Rpw protein, mouse; D025521:Tumor Suppressor Proteins; D000584:Amiloride; D012964:Sodium; D010447:Peptide Hydrolases