The renal H,K-ATPases.
OBJECTIVE
We integrate recent evidence that demonstrates the importance of the gastric (HKalpha1) and nongastric (HKalpha2)-containing hydrogen potassium adenosine triphosphatases (H,K-ATPases) on physiological function and their role in potassium (K), sodium (Na), and acid-base balance.


RESULTS
Previous studies focused on the primary role of H,K-ATPases as a mechanism of K conservation during states of K deprivation. Both isoforms function in H secretion and K absorption in vivo during K deprivation, but recent findings show that these pumps also function in acid secretion in animals fed normal K-replete diets. The complicated pharmacological inhibition of both pumps is reviewed. Interestingly, HKalpha2-null mice have a reduced expression and activity of the renal epithelial Na channel alpha subunit in the colon. When the human nongastric isoform was studied in a heterologous expression system with its cognate beta subunit (NaKbeta1), the pump exhibited substantial Na affinity at the 'K'-binding site. Evidence cited herein raises the possibility that either directly or indirectly the renal HKalpha2-containing H,K-ATPase may affect Na balance.


CONCLUSIONS
Both H,K-ATPase isoforms are active in normal animals and not just under conditions of K depletion. The possibility that either one or both isoforms contribute to Na absorption, particularly in humans, raises important clinical implications for these pumps in the kidney.
Greenlee
Megan M
MM
Research Service, North Florida/South Georgia Veterans Health System, USA.
Lynch
Irma Jeanette
IJ
Gumz
Michelle L
ML
Cain
Brian D
BD
Wingo
Charles S
CS
D000138:Acidosis / Q000201:enzymology; D000818:Animals; D017506:H(+)-K(+)-Exchanging ATPase / Q000032:analysis / Q000502:physiology*; D006801:Humans; D017136:Ion Transport; D007668:Kidney / Q000201:enzymology*; D011191:Potassium Deficiency / Q000201:enzymology; D012964:Sodium / Q000378:metabolism
D012964:Sodium; D017506:H(+)-K(+)-Exchanging ATPase