Aldosterone Rapidly Activates Na⁺/H⁺ Exchange in M-1 Cortical Collecting Duct Cells via a PKC-MAPK Pathway

Background: In this study, the mechanism of the rapid non-genomic effect of aldosterone on Na⁺/H⁺ exchanger (NHE)-mediated intracellular pH (pHi) recovery from an acid load in murine M-1 cortical collecting duct cells was assessed. Methods: Spectrofluorescence microscopy and Western blot analysis was carried out and NH₄Cl was used to induce the acid load. Results: Aldosterone (10 nM) induced a rapid (<5 min) concentration-dependent increase in pHi recovery in M-1 cells, an effect mimicked by its precursor deoxycorticosterone (1 nM). This response was unaffected by the mineralocorticoid receptor (MR) antagonist spironolactone (10 µM) but was significantly reduced by the NHE antagonists 5′-(N-ethyl- N-isopropyl)amiloride (EIPA) (20 µM) and cariporide (1 µM). The PKC inhibitor chelerythrine chloride (1 µM) significantly attenuated the aldosterone-induced increase in NHE1 activity. HBDDE (80 µM), a PKCα inhibitor, inhibited the rapid aldosterone effect whereas rottlerin (15 µM), a PKCδ antagonist, did not. The glucocorticoid receptor agonists hydrocortisone (1 µM) and dexamethasone (100 nM) decreased NHE activity, whereas the synthetic mineralocorticoid fludrocortisone (1 nM) had no significant effect. MAPK inhibition using PD98059 (25 µM) significantly attenuated the rapid aldosterone effect; Western blot analysis showed that aldosterone activation of ERK 1/2 was unaffected by pretreatment with spironolactone but was inhibited following chelerythrine chloride. Conclusion: Aldosterone causes a rapid non-genomic increase in NHE1 activity in M-1 cells via a PKCα/MAPK pathway independent of the classical MR.