Role of paraoxonase 3 in regulating ENaC-mediated Na(+) transport in the distal nephron.

Paraoxonase 3 (PON3) is expressed in the aldosterone-sensitive distal nephron, where filtered Na(+) is reabsorbed mainly via the epithelial Na(+) channel (ENaC) and Na(+) -coupled co-transporters. We previously showed that PON3 negatively regulates ENaC through a chaperone mechanism. The present study aimed to determine the physiological role of PON3 in renal Na(+) and K(+) homeostasis. Pon3 knockout (KO) mice had higher amiloride-induced natriuresis and lower plasma [K(+) ] at baseline. Single channel recordings in split-open tubules showed that the number of active channels per patch was significantly higher in KO mice, resulting in a higher channel activity in the absence of PON3. Although whole kidney abundance of ENaC subunits was not altered in Pon3 KOs, ENaC gamma subunit was more apically distributed within the connecting tubules and cortical collecting ducts of Pon3 KO kidneys. Additionally, small interfering RNA-mediated knockdown of PON3 in cultured mouse cortical collecting duct cells led to an increased surface abundance of ENaC gamma subunit. As a result of lower plasma [K(+) ], sodium chloride co-transporter phosphorylation was enhanced in the KO kidneys, a phenotype that was corrected by a high K(+) diet. Finally, PON3 expression was upregulated in mouse kidneys under dietary K(+) restriction, potentially providing a mechanism to dampen ENaC activity and associated K(+) secretion. Taken together, our results show that PON3 has a role in renal Na(+) and K(+) homeostasis through regulating ENaC functional expression in the distal nephron. KEY POINTS: Paraoxonase 3 (PON3) is expressed in the distal nephron of mouse kidneys and functions as a molecular chaperone to reduce epithelial Na(+) channel (ENaC) expression and activity in heterologous expression systems. We examined the physiological role of PON3 in renal Na(+) and K(+) handling using a Pon3 knockout (KO) mouse model. At baseline, Pon3 KO mice had lower blood [K(+) ], more functional ENaC in connecting tubules/cortical collecting ducts, higher amiloride-induced natriuresis, and enhanced sodium chloride co-transporter (NCC) phosphorylation. Upon challenge with a high K(+) diet, Pon3 KO mice had normalized blood [K(+) ] and -NCC phosphorylation but lower circulating aldosterone levels compared to their littermate controls. Kidney PON3 abundance was altered in mice under dietary K(+) loading or K(+) restriction, providing a potential mechanism for regulating ENaC functional expression and renal Na(+) and K(+) homeostasis in the distal nephron.