Paracellular Cl- permeability is regulated by WNK4 kinase: insight into normal physiology and hypertension.
Paracellular ion flux across epithelia occurs through selective and regulated pores in tight junctions; this process is poorly understood. Mutations in the kinase WNK4 cause pseudohypoaldosteronism type II (PHAII), a disease featuring hypertension and hyperkalemia. Whereas WNK4 is known to regulate several transcellular transporters and channels involved in NaCl and K+ homeostasis, its localization to tight junctions suggests it might also regulate paracellular flux. We performed electrophysiology on mammalian kidney epithelia with inducible expression of various WNK4 constructs. Induction of wild-type WNK4 reduced transepithelial resistance by increasing absolute chloride permeability. PHAII-mutant WNK4 produced markedly larger effects, whereas kinase-mutant WNK4 had no effect. The electrochemical and pharmacologic properties of these effects indicate they are attributable to the paracellular pathway. The effects of WNK4 persist when induction is delayed until after tight-junction formation, demonstrating a dynamic effect. WNK4 did not alter the flux of uncharged solutes, or the expression or localization of selected tight-junction proteins. Transmission and freeze-fracture electron microscopy showed no effect of WNK4 on tight-junction structure. These findings implicate WNK signaling in the coordination of transcellular and paracellular flux to achieve NaCl and K+ homeostasis, explain PHAII pathophysiology, and suggest that modifiers of WNK signaling may be potent antihypertensive agents.
Department of Genetics, Howard Hughes Medical Institute, Yale University School of Medicine, New Haven, CT 06510, USA.
Kristopher T
KT
Kahle
Gordon G
GG
Macgregor
Frederick H
FH
Wilson
Alfred N
AN
Van Hoek
Dennis
D
Brown
Thomas
T
Ardito
Michael
M
Kashgarian
Gerhard
G
Giebisch
Steven C
SC
Hebert
Emile L
EL
Boulpaep
Richard P
RP
Lifton
D019943:Amino Acid Substitution; D000818:Animals; D002460:Cell Line; D002463:Cell Membrane Permeability / Q000502:physiology*; D002712:Chlorides / Q000378:metabolism*; D018076:DNA, Complementary / Q000235:genetics; D004285:Dogs; D005614:Freeze Fracturing; D006973:Hypertension / Q000503:physiopathology*; D007668:Kidney; D008564:Membrane Potentials; D051379:Mice; D016297:Mutagenesis, Site-Directed; D018408:Patch-Clamp Techniques; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000502:physiology*; D011994:Recombinant Proteins / Q000378:metabolism; D019108:Tight Junctions / Q000502:physiology* / Q000648:ultrastructure; D019459:Urothelium / Q000502:physiology
D002712:Chlorides; D018076:DNA, Complementary; D011994:Recombinant Proteins; C499024:Prkwnk4 protein, mouse; D017346:Protein Serine-Threonine Kinases