To maintain potassium homeostasis, the kidney’s distal convoluted tubule (DCT) evolved to convert small changes in blood [K+] into robust effects on salt reabsorption. This process requires NaCl cotransporter (NCC) activation by the With-No-Lysine (WNK) kinases. During hypokalemia, the Kidney-Specific WNK1 isoform (KS-WNK1) scaffolds the DCT-expressed WNK signaling pathway within biomolecular condensates of unknown function termed WNK bodies. Here, we show that KS-WNK1 amplifies kidney tubule reactivity to blood [K+], in part via WNK bodies. Genetically modified mice with targeted condensate disruption trap the WNK pathway, causing renal salt wasting that is more pronounced in females. In humans, WNK bodies accumulate as plasma potassium falls below 4.0 mmol/L, suggesting that the human DCT experiences the stress of potassium deficiency even when [K+] is in the low-normal range. These data identify WNK bodies as kinase signal amplifiers that mediate tubular [K+] responsiveness, nephron sexual dimorphism, and blood pressure salt-sensitivity. Our results illustrate how biomolecular condensate specialization can optimize a mammalian physiologic stress response that impacts human health.

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