Epithelial Na channels control the reabsorption of salt by the kidney. They are essential for adapting to different levels of sodium in the diet, and defects in their regulation can lead to hypertension. Aldosterone is the major hormonal factor influencing these channels, but the mechanisms by which regulation is exerted are not fully understood. We will test the hypothesis that changes in processing and distribution of channel protein is a major factor underlying this regulation. We will use a combination of electrophysiological techniques and immunoblotting using antibodies specific for the 3 channel subunits alpha, beta and gamma ENaC to examine changes in the total amount of protein, in the processing of protein by proteolytic and glycosylating enzymes, and the expression of protein at the cell surface, and to correlate these events with channel activity in rats during salt restriction and challenge with aldosterone. We will compare these effects on the channels with those of other Na transporters including NaCl and NaK2Cl cotransporters and the Na/H exchanger. We will then examine the behavior of these proteins during acute salt repletion, where large changes in Na excretion can occur in a few hours. In this scenario we will also examine the role of reduction in channel open probability in reducing Na reabsorption and facilitating Na excretion. We will alos examine the molecular mechanisms underlying the effects of Na on open probability using the Xenous oocyte expression system. Finally we will test the hypothesis that the serine/threonine kinase SGK is a key protein for control of channel activity by assessing the activation of channels in mice lacking the gene for this kinase. We will measure channel activity as well as channel protein in animals in which hormone levels are changed over a few hours (with hormone infusion), over a few days (short-term salt restriction) or over a week or more (long-term salt restriction, long-term hormone infusion). The results will further our understanding of how these channels are regulated in vivo. NARRATIVE Disregulation of epithelial Na channels underlies most forms of monogenic hypertension. Yet how channels are normally controlled by adrenal steroids and other hormones remains poorly understood. The work described in this proposal will elucidate how these control mechanisms work and will enhance our understanding of how hypertension develops and impact how it is treated.

National Institute of Health (NIH)
National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)
Research Project (R01)
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Cellular and Molecular Biology of the Kidney Study Section (CMBK)
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Ketchum, Christian J
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Weill Medical College of Cornell University
Schools of Medicine
New York
United States
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Gleason, Catherine E; Frindt, Gustavo; Cheng, Chih-Jen et al. (2015) mTORC2 regulates renal tubule sodium uptake by promoting ENaC activity. J Clin Invest 125:117-28
Carattino, Marcelo D; Mueller, Gunhild M; Palmer, Lawrence G et al. (2014) Prostasin interacts with the epithelial Na+ channel and facilitates cleavage of the ?-subunit by a second protease. Am J Physiol Renal Physiol 307:F1080-7
Patel, Ankit B; Frindt, Gustavo; Palmer, Lawrence G (2013) Feedback inhibition of ENaC during acute sodium loading in vivo. Am J Physiol Renal Physiol 304:F222-32
Frindt, Gustavo; Palmer, Lawrence G (2012) Regulation of epithelial Na+ channels by adrenal steroids: mineralocorticoid and glucocorticoid effects. Am J Physiol Renal Physiol 302:F20-6
Patel, Ankit B; Chao, Julie; Palmer, Lawrence G (2012) Tissue kallikrein activation of the epithelial Na channel. Am J Physiol Renal Physiol 303:F540-50
Frindt, Gustavo; Palmer, Lawrence G (2012) Effects of insulin on Na and K transporters in the rat CCD. Am J Physiol Renal Physiol 302:F1227-33
Frindt, Gustavo; Houde, VĂ©ronique; Palmer, Lawrence G (2011) Conservation of Na+ vs. K+ by the rat cortical collecting duct. Am J Physiol Renal Physiol 301:F14-20
Frindt, Gustavo; Palmer, Lawrence G (2010) Effects of dietary K on cell-surface expression of renal ion channels and transporters. Am J Physiol Renal Physiol 299:F890-7
Schreiner, Ryan; Frindt, Gustavo; Diaz, Fernando et al. (2010) The absence of a clathrin adapter confers unique polarity essential to proximal tubule function. Kidney Int 78:382-8
Frindt, Gustavo; Palmer, Lawrence G (2009) Surface expression of sodium channels and transporters in rat kidney: effects of dietary sodium. Am J Physiol Renal Physiol 297:F1249-55

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