Sexual Dimorphic Responses of Renal Transporters to High Salt Diet Favor More Diuresis in Females

We previously reported, in male rats, that high salt diet (HSD) increased proximal tubule (PT) Na + /H + exchanger phosphorylation (NHE3pS552), a marker of its inactivation, depressed total abundance of distal tubule Na + ‐Cl − cotransporter (NCC), and redistributed apical Na + transporters to higher density fractions (Yang LE, AJP Renal, 2008). Female rats and mice have lower abundance of proximal tubule sodium transporters (NHE3, NaPi2) and higher abundance and phosphorylation (activation) of NCC as well as cleaved (activated) epithelial sodium channels' (ENaC) α and g subunits (FASEB J, 2016, 30: Supp 967.29). Female mice also have a more robust pressure natriuretic response than males (Mirabito KM et al , AJP Renal, 2014). Based on this background, this study aimed to compare the responses of females (F) and males (M) to high salt diet; we postulated that F would exhibit more robust responses than M. Methods C57Bl/6 mice (n=5/group) received normal salt diet (0.26% NaCl; MNS: males normal salt; FNS: females normal salt) or a high salt diet (4.0% NaCl; MHS: males high salt; FHS: females high salt) for two weeks. Transporter and channel abundance were determined by quantitative immunoblot in homogenates of renal cortex. The Figure displays the fold change in the abundance of transporters and channels after HSD, relative to NSD in F and M. Results Females had a greater diuretic response to HSD (6 fold) than M (ns). At baseline, F had lower PT NHE3 (0.6‐fold) and lower NHE3pS552 (0.7‐fold) than M. NHE3pS552 increased 0.2‐fold in MHS, and was unchanged in FHS. Along the loop and distal nephron, there was no significant difference in Na + ‐K + ‐2Cl − cotransporter isoform 2 (NKCC2), NKCC2pT96T101, NCC, or NCCpS71 at baseline, yet SPAK, a regulatory kinase that phosphorylates these cotransporters and claudin 7 were elevated in F (0.5‐ and 0.7‐fold, respectively). In FHS NKCC2, NKCC2pT96T101, NCC, and NCCpS71 were lower than FNS (0.2‐, 0.5‐, 0.3‐, 0.5‐fold, respectively) and in MHS vs. MNS only NCC decreased (0.2‐fold) suggesting less Na + reabsorption in this nephron region in F vs. M. In collecting duct at baseline, ENaC γ was higher in F than M (0.15‐fold) and doubled in both FHS and MHS vs. NS. ENaC γ subunit cleavage decreased 0.2‐fold only in MHS. Taken together, these results demonstrate that the responses to HS diet are sex dependent. The more robust diuresis in FHS can be attributed to lower PT NHE3 at baseline as well as reduced NKCC2, NKCC2pT96T101, NCC and NCCpS71 during HS diet. These characteristics likely facilitate pressure natriuresis and contribute to lower blood pressures in females. Support or Funding Information NIH R01DK 083785, AHA 15GRNT23160003