Cs. Chang et al., PRESENCE OF IMMUNOREACTIVE ALPHA-3 SUBUNIT ISOFORM OF NA,K-ATPASE IN MITOCHONDRIA OF KIDNEY, Kidney international, 54(2), 1998, pp. 457-463
Background. Sodium-potassium-adenosinetriphosphatase (Na,K-ATPase) is
the primary membrane enzyme responsible for the reabsorption of sodium
ions in the kidney. It is known that in the nephron the major subunit
isoforms of Na,K-ATPase are alpha 1 and beta 1. Previous reports on t
he presence of alpha 2 and alpha 3 isoforms in the kidney were mixed a
nd controversial. Methods. Techniques of ultrathin cryosectioning and
immunoelectron microscopy were used to study the distribution of alpha
subunit isoforms (alpha, alpha 2, alpha 3) and beta subunit (beta 1 i
soform) of Na,K-ATPase in renal tubular cells. Western blot analysis w
as used to show the presence of the alpha 3 isoform in the extract of
kidney mitochondria. Results. We were able to confirm the previous fin
ding that the alpha 1 isoform and the beta 1 isoform were the preponde
rant isoforms of the alpha and beta subunits of Na,K-ATPase in the bas
olateral membrane. In addition, we unexpectedly found the presence of
the alpha 3 isoform in the mitochondria of rat renal tubular cells. Th
e alpha 2 and alpha 3 isoforms were not observed in either the apical
or basolateral membrane. Conclusions. Both immunoelectron microscopy a
nd Western blot analysis of the rat kidney mitochondria confirm the pr
esence of the alpha 3 isoform of Na,K-ATPase in the rat kidney mitocho
ndria. The function of this enzyme in the mitochondria is not clear at
this time.