The distal convoluted tubule (DCT) NaCl cotransporter NCC is activated by phosphorylation, a process that is potassium-regulated and dependent on With-No-Lysine (WNK) kinases. KS-WNK1, a kidney-specific WNK1 isoform lacking the kinase domain, controls WNK signaling pathway localization in the DCT. Its role in NCC regulation, however, is unresolved: while early studies proposed that KS-WNK1 functions as an NCC inhibitor, recent work suggests that it activates NCC. To evaluate the role of KS-WNK1 on potassium-dependent NCC regulation, we studied KS-WNK1-KO mice across a wide range of plasma K+ (2.0-9.0 mmol/L), induced by dietary maneuvers and diuretic challenges. Potassium-deprived KS-WNK1-KO mice exhibited low WNK-dependent NCC phosphorylation compared to littermates, indicating that KS-WNK1 activates NCC during K+ deficiency. In contrast, relative NCC phosphorylation was high in potassium-loaded KS-WNK1-KO mice, consistent with KS-WNK1-mediated NCC inhibition during hyperkalemia. An integrated analysis revealed that KS-WNK1 expands the dynamic range of NCC responsiveness to potassium, steepening the linear inverse relationship between NCC phosphorylation and plasma [K+]. The effect of KS-WNK1 deletion was strongest in potassium-restricted females, as they developed exaggerated hypokalemia and thiazide insensitivity due to low NCC activity. Taken together, these findings indicate that KS-WNK1 is a potassium-responsive signaling amplifier that converts small changes in [K+] into large effects on NCC phosphorylation. This effect predominates in females during potassium deficiency, when high NCC activity is required to maintain salt reabsorption without exacerbating K+ losses. These observations define the role of KS-WNK1 in NCC regulation, and identify a novel mechanism that contributes to sexual dimorphism in the mammalian nephron.
