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1 Physiology and Biophysics, University of Alabama at Birmingham, Birmingham, AL, USA
2 Cell Biology, University of Alabama at Birmingham, Birmingham, AL, USA
3 Pediatrics and Medicine, Mount Sinai School of Medicine, New York, NY, USA
4 Physiology and Biophysics, University of Alabama at Birmingham, Birmingham, AL, USA; Nephrology, University of Alabama at Birmingham, Birmingham, AL, USA
5 Cell Biology, University of Alabama at Birmingham, Birmingham, AL, USA; Nephrology, University of Alabama at Birmingham, Birmingham, AL, USA; Genetics and Translational Medicine, University of Alabama at Birmingham, Birmingham, AL, USA
6 Physiology and Biophysics, University of Alabama at Birmingham, Birmingham, AL, USA; Cell Biology, University of Alabama at Birmingham, Birmingham, AL, USA; Nephrology, University of Alabama at Birmingham, Birmingham, AL, USA
* To whom correspondence should be addressed. E-mail: issytman{at}uab.edu.
The Tg737orpk autosomal recessive polycystic kidney disease (ARPKD) mouse carries a hypomorphic mutation in the Tg737 gene. Due to the absence of its protein product Polaris, the non-motile primary monocilium central to the luminal membrane of ductal epithelia such as the cortical collecting duct (CCD) principal cell (PC) is malformed. While functions of the renal monocilium remain elusive, primary monocilia or flagella on neurons act as sensory organelles. Thus, we hypothesize that the PC cell monocilium functions as a cellular sensor. To this end, we assessed the contribution of Polaris and cilium structure and function to renal epithelial ion transport electrophysiology. Properties of Tg737orpk mutant CCD PC clones were compared with clones genetically rescued with wild-type Tg737 cDNA. All cells were grown as polarized cell monolayers with similar very high transepithelial resistance (RTE) on permeable filter supports. Three to 4-fold elevated transepithelial voltage (VTE) and short-circuit current (ISC) was measured in mutant orpk monolayers versus rescued controls. Pharmacological and cell biological examination of this enhanced electrical endpoint in mutant monolayers revealed that ENaC sodium (Na+) channels were upregulated. Amiloride, ENaC-selective amiloride analogs (benzamil, phenamil), and protease inhibitors (aprotinin and leupeptin) attenuated heightened transepithelial voltage and current. Higher concentrations of additional amiloride analogs (ethylisopropylamiloride, dimethylamiloride) also revealed inhibition of VTE. Cell culture requirements and manipulations were also consistent with heightened ENaC expression and function. Taken together, these data suggest that ENaC expression and/or function is upregulated in the luminal membrane of mutant, cilium-deficient orpk CCD PC cell monolayers versus 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 human ARPKD patients.
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 M. A. Gray Primary cilia and regulation of renal Na+ transport. Focus on "Heightened epithelial Na+ channel-mediated Na+ absorption in a murine polycystic kidney disease model epithelium lacking apical monocilia" Am J Physiol Cell Physiol, April 1, 2006; 290(4): C947 - C949. [Full Text] [PDF]
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