Abstract
The epithelial sodium channel (ENaC) is believed to represent the rate-limiting step for sodium absorption in the renal collecting duct. Consequently, ENaC is a central effector affecting systemic blood volume and pressure. Sodium and water transport are dysregulated in diabetes mellitus. Peroxisome proliferator-activated receptor γ (PPARγ) agonists are currently used in the treatment of type 2 diabetes, although their use remains limited by fluid retention. The effects of PPARγ agonists on ENaC activity remain controversial. Although PPARγ agonists were shown to stimulate ENaC-mediated renal salt absorption, probably via the serum- and glucocorticoid-regulated kinase 1, other studies reported that the PPARγ agonist-induced fluid retention is independent of ENaC activity. Here we confirmed that four chemically distinct PPARγ agonists [pioglitazone, rosiglitazone, troglitazone, and 15-deoxy-Δ12,14-prostaglandin J2 (PGJ2)] do not enhance Na+ transport in cultured renal collecting duct principal mpkCCDc14 cells, as assessed by short-circuit current measurements. However, the PPARγ antagonist 2-chloro-5-nitro-N-4-pyridinyl-benzamide (T0070907), and to a lesser extent 2-chloro-5-nitrobenzanilide (GW9662), were found to decrease Na+ reabsorption across mpkCCDc14 cell layers. Furthermore, pretreatment of monolayers with T0070907 diminished the insulin-stimulated sodium transport. PPARγ agonist PGJ2 did not enhance insulin-stimulated Na+ flux via ENaC. We also show that PPARγ enhances ENaC activity when all three subunits are reconstituted in Chinese hamster ovary (CHO) cells. GW9662 inhibits ENaC activity when ENaC subunits are coexpressed in CHO cells with PPARγ. In contrast, rosiglitazone has no effect on ENaC activity. We conclude that PPARγ activity is important for maintaining basal and insulin-dependent transepithelial Na+ transport and ENaC activity.
Footnotes
This work was supported by the American Heart Association [Grant 0730111N]; a Carl W. Gottschalk Research Scholar Grant from the American Society of Nephrology; and Medical College of Wisconsin Research Affairs Committee New Faculty Grant.
Article, publication date, and citation information can be found at http://molpharm.aspetjournals.org.
doi:10.1124/mol.109.056911
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ABBREVIATIONS:
- ENaC
- epithelial Na+ channel
- PPAR
- peroxisome proliferator-activated receptor
- PGJ2
- 15-deoxy-Δ12,14-prostaglandin J2
- SGK1
- serum- and glucocorticoid-regulated kinase 1
- T0070907
- 2-chloro-5-nitro-N-4-pyridinyl-benzamide
- CHO
- Chinese hamster ovary
- TZD
- thiazolidinedione
- DMEM
- Dulbecco's modified Eagle's medium
- MTT
- 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide
- MES
- 2-(N-morpholino)ethanesulfonic acid
- CFTR
- cystic fibrosis transmembrane regulator
- GW9662
- 2-chloro-5-nitrobenzanilide
- ASIC
- acid sensing ion channel protein
- CD
- collecting duct
- P450
- cytochrome P450
- GW7845
- (S)-2-(1-carboxy-2-{4-[2-(5-methyl-2-phenyloxazol-4-yl)ethoxy]phenyl}ethylamino)benzoic acid methyl ester.
- Received April 7, 2009.
- Accepted September 10, 2009.
- © 2009 The American Society for Pharmacology and Experimental Therapeutics
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