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1 Physiology, Emory University School of Medicine, Atlanta, GA, USA
2 Division of Pulmonary, Allergy, and Critical Care Medicine, Atlanta Veterans Affairs, Atlanta, GA, USA
* To whom correspondence should be addressed. E-mail: deaton{at}physio.emory.edu.
Several studies have shown that nitric oxide (NO) inhibits Na+ transport in renal and alveolar monolayers. However, the mechanisms by which NO alters epithelial sodium channel (ENaC) activity is unclear. Therefore, we examined the effect of applying NO-donor drug L-propanamine, 3-2-hydroxy-2-nitroso-1-propylhidrazino (PAPA-NONOate) to cultured renal epithelial cells. A6 and M-1 cells were maintained on permeable supports in medium containing 1.5µM dexamethasone and 10% bovine serum. After applying 1.5µM PAPA NONOate, amiloride-sensitive short circuit current measurements decreased 29% in A6 cells, and 44% in M-1 cells. This differed significantly from the 3% and 19% decrease in A6 and M-1 cells, respectively, treated with control donor compound (P<0.0005). Subsequent application of PAPA NONOate to amiloride treated control (no NONOate) A6 and M-1 cells did not further decrease transepithelial current. In single channel patch clamp studies, NONOate significantly decreased amiloride-sensitive sodium channel open probability (Po) from .186±.043 to .045±.009 (*P<.05 and n=7) without changing the unitary current. We also showed that aldosterone significantly decreases NO production in primary cultures of alveolar type II (ATII) epithelial cells. Since iNOS co-immunoprecipitated with the serum- and glucocorticoid- inducible kinase (SGK1) and both proteins co-localized in the cytoplasm (as shown in our studies in mouse ATII cells), SGK1 may also be important in regulating NO production in the alveolar epithelium. Our study also identified iNOS as a novel SGK1 phosphorylated protein (at Ser733 and S903 residues in miNOS) suggesting that one way in which SGK1 could increase Na+ transport is by altering iNOS production of NO.
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