Role of Mineralocorticoid receptor (MR) and NEDD4‐2 in the regulation of ENaC and ROMK in the Distal Convoluted Tubule (DCT) and Cortical Collecting Duct (CCD)

Abstract

BackgroundENaC and ROMK (Kir1.1) are expressed in the apical membrane of aldosterone‐sensitive distal nephron (ASDN). Aldosterone has been shown to play an important role in the regulation of ENaC and ROMK expression in ASDN. Also, NEDD4‐2 is an E3 ubiquitin ligase expressed in the ASDN and NEDD4‐2 has been shown to play a role in mediating the effect of aldosterone on ENaC. The aims of the present study are:1) To examine whether MR plays a similar role in regulating ENaC and ROMK in the DCT2 and CCD; 2) To examine whether NEDD4‐2 regulates ROMK channels in ASDN.MethodsThe whole‐cell recording technique has been used to measure the amiloride‐sensitive Na currents (ENaC) at −60 mV and TPNQ‐sensitive K currents (ROMK) at −40 mV in the DCT2/early connecting tubule (CNT) and in the CCD of tubule‐specific MR‐KO, NEDD4‐2 KO and corresponding WT mice on a normal rodent diet (0.4% Na and 0.9% K).ResultsDeletion of MR receptor decreased ENaC currents from10.2 pA/pf to 6.3 pA/pf (at −60 mV) in the DCT2/CNT but it largely abolished ENaC currents in the CCD (from 4.9 pA/pf to 0.7 pA/pf). In contrast, the deletion of MR had no significant effect on ROMK currents in the DCT2 since TPNQ‐sensitive K currents were the same between WT and Ks‐MR‐KO mice (WT, 51.0 pA/pf; Ks‐MR‐KO, 50.0 pA/pf at −40 mV). However, the ROMK currents of the CCD were significantly smaller in MR‐KO (22.1 pA/pf) than in WT (33.8 pA/pf), suggesting that MR plays a role in regulating ROMK only in the CCD but not in the DCT2/CNT. Deletion of NEDD4‐2 increased amiloride sensitive Na currents from 10 pA/pf to 13 pA/pf in the DCT2/CNT but it robustly increased ENaC currents from 5.1 pA/pf to 15 pA/pf in the CCD, suggesting that NEDD4‐2 plays a bigger role in regulating ENaC in the CCD than in the DCT2/CNT. Deletion of NEDD4‐2 inhibited rather than stimulated ROMK channel activity in both DCT2/CNT and in the CCD. TPNQ‐sensitive K currents were decreased from 46 pA/pf (WT) to 24.6 pA/pf (NEDD4‐2 KO) in the DCT2/CNT and from 34 pA/pf (WT) to 23.6 pA/pf (NEDD4‐2) in the CCD.ConclusionMR plays a key role in the regulation of ENaC in the CCD but to a less degree in the DCT2/CNT. ROMK channel activity is modestly regulated by MR in the CCD but not in the DCT2/CNT. NEDD4‐2 plays a role in the down‐regulation of ENaC activity in the ASDN, especially in the CCD, but it may not directly regulate ROMK.Support or Funding InformationDK54983