Abstract:
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Background/Aims: The WNK-dependent STE20/SPS1-related proline/alanine-rich kinase
SPAK participates in the regulation of NaCl and Na+,K+,2Cl- cotransport and thus renal salt
excretion. The present study explored whether SPAK has similarly the potential to regulate
the epithelial Na+ channel (ENaC). Methods: ENaC was expressed in Xenopus oocytes with or
without additional expression of wild type SPAK, constitutively active T233ESPAK, WNK insensitive
T233ASPAK or catalytically inactive D212ASPAK, and ENaC activity estimated from amiloride (50
μM) sensitive current (Iamil) in dual electrode voltage clamp experiments. Moreover, Ussing
chamber was employed to determine Iamil in colonic tissue from wild type mice (spakwt/wt) and
from gene targeted mice carrying WNK insensitive SPAK (spaktg/tg). Results: Iamil was observed
in ENaC-expressing oocytes, but not in water-injected oocytes. In ENaC expressing oocytes
Iamil was significantly increased following coexpression of wild-type SPAK and T233ESPAK, but not
following coexpression of T233ASPAK or D212ASPAK. Colonic Iamil was significantly higher in spakwt/
wt than in spaktg/tg mice. Conclusion: SPAK has the potential to up-regulate ENaC. |