WNK4 orchestrates differential responses to hypovolemia and hyperkalemia. WNK4 has at least three distinct functional states defined by the effects of wild-type WNK4, PHAII-mutant WNK4, and WNK4S1169D on downstream targets. The effects at two of these targets, ROMK and ENaC, are shown. We propose that intravascular volume depletion (Low IV Volume) and hyperkalemia (High K+), which are associated with either aldosterone plus angiotensin II (aldo + AII) or aldosterone alone, respectively, have differential effects at downstream targets. At equilibrium, WNK4 inhibits both ENaC and ROMK. PHAII mutation defines a state that alleviates inhibition of ENaC while augmenting inhibition of ROMK, promoting a net increase in renal Na+ reabsorption without K+ loss. Hyperkalemia results in increased aldosterone signaling, phosphorylation of the SGK1 site, and loss of WNK4 inhibition of both ENaC and ROMK. This results in a net increase in K+ secretion via increases in both the electrical driving force for K+ secretion and K+ channel activity.