(A) Western blot analyses showing effects of WT (aa 1–491) versus kinase-dead WNK1 mutant (aa 1–491) (K233M) on extracellular [K+]–stimulated phosphorylation of SGK1. WNK1-deficient HEK-293 cells were transfected with FLAG-SGK1 and WNK1 (aa 1–491) WT or (aa 1–491) K233M. Cells were adapted to 1 mM [K+], and then media [K+] was either raised to 5 mM or kept at 1 mM for 1 hour. In cells lacking WT or WNK1 K233M, raising extracellular [K+] to 5 mM failed to stimulate SGK1 phosphorylation. Cells expressing K233M exhibited higher abundance of p-SGK1 compared with cells expressing WT WNK1. (B) Quantification of the Western blot data, presented as mean ± SEM from 3 independent experiments. **P < 0.01, ****P < 0.0001 by 1-way ANOVA. NS, not significant.