With no lysine kinase 4 modulates sodium potassium 2 chloride cotransporter activity in vivo

Abstract

With no lysine kinase 4 (WNK4) is essential to activate the thiazide-sensitive NaCl cotransporter (NCC) along the distal convoluted tubule, an effect central to the phenotype of familial hyperkalemic hypertension. Although effects on potassium and sodium channels along the connecting and collecting tubules have also been documented, WNK4 is typically believed to have little role in modulating sodium chloride reabsorption along the thick ascending limb of the loop of Henle. Yet wnk4 mice (knockout mice lacking WNK4) do not demonstrate the hypocalciuria typical of pure distal convoluted tubule dysfunction. Here, we tested the hypothesis that WNK4 also modulates bumetanide-sensitive Na-K-2Cl cotransporter (NKCC2) function along the thick ascending limb. We confirmed that w nk4 mice are hypokalemic and waste sodium chloride, but are also normocalciuric. Results from Western blots suggested that the phosphorylated forms of both NCC and NKCC2 were in lower abundance in wnk4 mice than in controls. This finding was confirmed by immunofluorescence microscopy. Although the initial response to furosemide was similar in wnk4 mice and controls, the response was lower in the knockout mice when reabsorption along the distal convoluted tubule was inhibited. Using HEK293 cells, we showed that WNK4 increases the abundance of phosphorylated NKCC2. More supporting evidence that WNK4 may modulate NKCC2 emerges from a mouse model of WNK4-mediated familial hyperkalemic hypertension in which more phosphorylated NKCC2 is present than in controls. These data indicate that WNK4, in addition to modulating NCC, also modulates NKCC2, contributing to its physiological function in vivo.

WNK4 limits distal calcium losses following acute furosemide treatment

“…Here, we investigate the role of WNK4 in calcium transport along the TAL and DCT using WNK4 −/− animals. While baseline urinary calcium levels are known to be normal in WNK4 −/− animals (Castaneda‐Bueno et al ; Terker et al ), we have reported differences in urine calcium excretion between controls and knockout animals in response to dietary stress (Terker et al ). We sought to determine the role of WNK4 in calcium handling under conditions known to perturb calcium homeostasis.…”

“…The loop diuretic furosemide causes hypercalciuria, both chronically and acutely. We reported decreased furosemide‐induced natriuresis in WNK4 −/− mice (Terker et al ). To determine effects of WNK4 deletion on furosemide‐induced calcium excretion, we quantified urine calcium following acute furosemide treatment.…”

“…WNK4 −/− mice have normal urine calcium excretion at baseline (Castaneda‐Bueno et al ; Terker et al ), but the role of WNK4 in regulating calcium handling under conditions known to perturb calcium homeostasis remains unclear. The loop diuretic furosemide causes hypercalciuria, both chronically and acutely.…”

“…Studies using WNK4 null animals have demonstrated the importance of the WNK4‐SPAK/OxSR1‐NCC pathway along the DCT for regulation of sodium and potassium homeostasis in vivo (Castaneda‐Bueno et al (); Takahashi et al ). Using this same model, we recently reported that WNK4 is also important for sodium transport along the TAL (Terker et al ).…”

Hypochloraemia in Patients with Heart Failure: Causes and Consequences

“…The with-no-lysine (WNK) kinases (WNK1, WNK3, and WNK4) are the first step in an enzymatic cascade which increases activity of the Na + /K + /2Cl − and Na + /Cl − co-transporters [ 40 – 43 ]. Chloride binds to the catalytic site of the kinases, thus inactivating them [ 44 , 45 ].…”