The role of mineralocorticoid receptor in the potassium switch: effect on NCC regulation .

Thiazide sensitive sodium-chloride cotransporter (NCC) is a major salt transport pathway in the apical membrane of the nephron distal convoluted tubule. While we know the importance of its function in maintaining sodium-potassium homeostasis, the regulation of NCC is complicated and the mechanisms are not well understood. The aim of this study is to evaluate the role of mineralocorticoid receptors (MRs) in the regulation of NCC. Here, we generated DCT-specific MRs Knockout (KO) mice, in which MRs were deleted in cells expressing NCC, taking advantage of a cre recombinase under the control of the NCC gene. Under standard and Low-Na+ diets, these DCT-specific MRs-KO mice display normal Na /K balance but exhibit problems with Cl- regulation. These KO mice presented hypochloremia under normal diet but unexpectedly, hyperchloremia after 6d on low Na+ diet. The expression of NCC and phosphorylated NCC were both decreased in KO mice compared to that in control mice, under both standard and low-Na diet. This decrease in NCC protein levels is related to a decrease in transcription levels. Under standard diet, decreased NCC expression is compensated by an increase in αENaC and pendrin expression, which is not the case under low-salt diet. Under a low-K diet, KO mice exhibit hypokalemia and volume depletion with increased blood CO levels and Renin mRNA levels. NCC expression and its phosphorylation are both increased in control and KO groups under low-K diet compared to standard diet but, the levels of NCC protein and mRNA are still decreased in the KO group compared to the control group mice. Taken together, these results demonstrate that MRs is not necessary for the complete regulation of NCC under low-Na+ and low-K+ diet. On the other hand, MRs appears to be indispensable to assure proper NCC expression in adult DCT renal tubules.