The gamma-Na+,K+-ATPase subunit assembles selectively with alpha1/beta1-Na+,K+-ATPase but not with the colonic H+,K+-ATPase.
BACKGROUND
The ubiquitous Na+-pump (Na+,K+-ATPase) assembles as a heterodimer of composition alpha/beta in some nephron segments, while in other segments it may exist as a heterotrimer of composition alpha/beta/gamma. The gamma-subunit has been reported to increase the affinity of the Na+-pump for adenosine 5'-triphosphate (ATP), and decrease affinity for both Na+ and K+. The alpha-subunit of the colonic H+,K+-ATPase (cHK) shares 75% sequence similarity with alpha1-Na+,K+-ATPase (alpha1) and assembles with beta1-Na+,K+-ATPase (beta1) in distal colon and renal medulla. Differences in pharmacological properties have been ascribed to when heterologously expressed function has been compared to function in vitro. The purpose of this study was to determine if cHK might associate with the gamma-subunit of the Na+,K+-ATPase (gamma) as a possible explanation for these variations in function.


METHODS
An antibody specific for the gamma was used in coimmunoprecipitation experiments to determine if the gamma assembles stably in vitro with cHK and beta1 in rat renal medulla or distal colon.


RESULTS
Our results demonstrate that the gamma-subunit assembles specifically with the Na+-pump, but not with cHK. Furthermore, the gamma-subunit assembly was specific for rat kidney and was not observed in distal colon.


CONCLUSIONS
Since the gamma-subunit did not assemble with the cHK/beta1 complex, gamma-subunit assembly cannot explain those variations in ex vivo and in vitro pharmacologic properties ascribed to cHK.
Codina
Juan
J
Department of Internal Medicine and Kidney Institute, University of Kansas School of Medicine, Kansas City, KS, USA.
Li
Jian
J
Hong
Yan
Y
DuBose
Thomas D
TD
D000818:Animals; D003106:Colon / Q000201:enzymology*; D017506:H(+)-K(+)-Exchanging ATPase / Q000378:metabolism*; D015151:Immunoblotting; D007679:Kidney Medulla / Q000201:enzymology*; D008297:Male; D011233:Precipitin Tests; D011499:Protein Processing, Post-Translational; D021122:Protein Subunits; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D000254:Sodium-Potassium-Exchanging ATPase / Q000235:genetics / Q000378:metabolism*
C503551:ATP1B1 protein, human; C503554:Atp1b1 protein, rat; D021122:Protein Subunits; D012333:RNA, Messenger; C498817:Fxyd2 protein, rat; D017506:H(+)-K(+)-Exchanging ATPase; D000254:Sodium-Potassium-Exchanging ATPase