PRESENCE OF IMMUNOREACTIVE ALPHA-3 SUBUNIT ISOFORM OF NA,K-ATPASE IN MITOCHONDRIA OF KIDNEY

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.