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Regulated Dephosphorylation of NCC Shapes the Renal Potassium Switch Pathway
Author(s) -
Grimm P. Richard,
Li Dimin,
Delpire Eric,
Welling Paul A.
Publication year - 2018
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.2018.32.1_supplement.620.12
Subject(s) - dephosphorylation , kinase , distal convoluted tubule , phosphorylation , endocrinology , chemistry , phosphatase , medicine , reabsorption , biochemistry , kidney , biology
The Renal Potassium Switch pathway stimulates the thiazide‐diuretic sensitive sodium chloride cotransporter (NCC) to limit urinary potassium loss at the expense of retaining sodium and elevating blood pressure. It has been established that Low [K + ] o activates the WNK4‐SPAK kinases to drive NCC phosphorylation, but it remains mysterious how NCC is dephosphorylated in response to an acute rise in [K + ] o . It has been generally assumed that high [K + ] o turns off WNK4 kinase activation, allowing constitutive phosphatase activity to dephosphorylate WNK4 in states of dietary potassium loading. Here, we challenge the prevailing view. Kinase‐activating mutations were introduced in SPAK, the terminal kinase in the WNK signaling pathway, and renal expression of the constitutively active (CA) SPAK mutant was specifically targeted in mice to the early DCT with a DCT‐driven Cre‐recombinase. NCC abundance (tNCC) and phosphorylation (pNCC) were evaluated in vivo and in isolated tubules, together with telemetric blood pressure (BP) measurements in response to changes in dietary potassium and [K + ] o . CA‐SPAK were compared to Control mice. CA‐SPAK mice display thiazide‐treatable hypertension, concurrent with NCC hyperphosphorylation. BP remained elevated in CA‐SPAK mice, compared to control, over a wide range of [K + ] o , as predicted. However, BP dropped in CA‐mice when [K + ] o exceeded 5 mM, and this was coincident with a reduction in pNCC/tNCC, revealing a [K + ]‐regulated dephosphorylation mechanism. In isolated control DCT tubules, an acute increase in [K + ] o rapidly reduced pNCC with IC50 of ~3.5 mM, indicating [K + ] o directly modulates dephosphorylation of the switch pathway. [K + ] o –regulated dephosphorylation of pNCC was also observed in DCT isolated from CA‐SPAK mice but the response displayed a rightward shift in the dependence on [K + ] o . Conclusion Because CA‐SPAK drives NCC phosphorylation independent and downstream of WNK, these observations provide strong support for a potassium‐activated phosphatase that directly dephosphorylates NCC. Thus [K + ] o –regulated phosphorylation as well as dephosphorylation of NCC shape the Renal Potassium Switch response. Regulated NCC dephosphorylation provides a new mechanism to explain why high dietary K + consumption alleviates salt‐sensitive hypertension and associated cardiovascular complications. Support or Funding Information Funding for this project was provided National Institutes of Health Grants DK63049, DK54231, and DK093501 This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal .