Defining corticosteroid-regulated sodium transport within the distal nephron
Authors: Mansley Morag , Milne Morag , Loughlin Struan , Um In Hwa , Hunter Robert , Bailey Matthew 
Published: May 2023

The aldosterone (ALDO)-sensitive distal nephron is typically defined as: the late distal convoluted tubule (DCT2), connecting tubule (CNT) and cortical collecting duct (CCD). ALDO-sensitivity is defined by 11βHSD2 (11β) activity (which inactivates corticosterone, CORT); mineralocorticoid (MR) rather than glucocorticoid receptor (GR) expression; and the target epithelial sodium channel (ENaC). Recent studies have reported ALDO-insensitive, but MR-dependent ENaC activity in DCT2/CNT and that CORT-stimulated ENaC may be relevant in MR antagonism as 4th line anti-hypertensive therapy. Whilst functional evidence of ALDO-insensitive ENaC activity is compelling, corticosteroid-regulated Na+ transport along the distal nephron is not fully defined. AIM: to determine 11βHSD2, MR and GR expression alongside Na+ transporter localisation in murine distal nephron and assess the endogenous receptor(s) underpinning steroid-stimulated ENaC activity.Male C57BL/6 mouse kidney sections were subject to multiplex immunofluorescence (11β, MR and GR) and immunohistochemical labelling (NCC, TRPV5, γ-ENaC and AQP2). Images were co-registered, annotated and analysed using Halo® software. Steroid-induced ENaC-mediated currents were measured in mCCDcl1 and primary CD cells. Carbenoxolone (CBX), mifepristone (MF) or PF-03882845 (PF) were used to inhibit 11β, GR and MR, respectively.Distal nephron segments were defined as: DCT - NCC; DCT/CNT - NCC and TRPV5; CNT - TRPV5; CNT/CCD - TRPV5 and γ-ENaC/AQP2; CCD - γ-ENaC/AQP2. We did not detect NCC and γ-ENaC co-localisation. Average cells/section, DCT: 874±39; DCT/CNT: 238±31; CNT: 198±63; CNT/CCD: 831±282; CCD: 2262±231 ( n=3). Negligible numbers of cells expressed both MR and GR.DCT was predominantly 11β- (~90%) and GR dominant (GR:MR ratio ~7:1). In 11β+ cells (~10%), GR was also dominant (GR:MR ratio ~4:1). DCT/CNT and CNT were mainly 11β- (~85 and ~75%, respectively), where MR and GR were similar. In 11β+ cells, MR and GR were similar in DCT/CNT but MR was greater in CNT (MR:GR ratio ~4:1). CNT/CCD contained a near equal split of 11β- (~52%) and 11β+ (~48%) cells. MR and GR were similar in 11β- cells, but 11β+ cells were almost exclusively MR (MR:GR ratio ~37:1). In CCD, ~35% of cells were 11β-, MR and GR were similar, and ~65% cells were 11β+, these were predominantly MR (MR:GR ratio ~30:1).In mCCDcl1 ( n=8-11) and primary CD cells ( n=6), ALDO-induced ENaC activity was inhibited by MR ( p<0.001) but not GR antagonists. DEX-induced ENaC activity was inhibited by GR ( p<0.001) but not MR antagonists. CORT-induced ENaC activity was modestly inhibited by MR ( p<0.05) but not by GR antagonists.Our data suggest that the DCT is a glucocorticoid-responsive segment, with 11β+ cells becoming progressively more dominant from CNT to CCD. The appearance of ENaC in the late CNT and particularly CCD, alongside 11β and MR, suggest these segments reflect the mineralocorticoid-responsive, and thus aldosterone-sensitive distal nephron. Kidney Research UK, The Royal Society This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.