NA-K-ATPASE ISOFORM (ALPHA(3), ALPHA(2), ALPHA(1)) ABUNDANCE IN RAT-KIDNEY ESTIMATED BY COMPETITIVE RT-PCR AND OUABAIN BINDING

For understanding the regulation of sodium reabsorption, it is importa nt to know whether the alpha(2)- or alpha(3)-isoform of Na-K-adenosine triphosphatase (Na-K-ATPase) is expressed in mammalian kidney in addit ion to the predominant alpha(1) beta(1)-isozyme. Here me applied compe titive polymerase chain reaction (PCR) for estimation of mRNA in paren chymal zones of rat kidney for comparison to high-affinity [H-3]ouabai n binding. The alpha(3)-isoform mRNA was demonstrated to form 0.04-0.0 5% of the amount of alpha(1)-isoform mRNA in the cortex, medulla, and papilla of rat kidney. The alpha(2)-mRNA was demonstrated in all three zones and constituted 0.03% of the amount of alpha(1)-mRNA in cortex. The abundance of the alpha(1) truncated mRNA was 0.1-0.8% of that of the alpha(1)-mRNA. The upper limit for expression of Na-K-ATPase isozy me with high ouabain affinity (dissociation constant, 69-141 nM) was 0 .096-0.14% of the concentration of alpha(1) beta(1)-Na-K-ATPase. Thus a small but well-defined pool of alpha(2)- and alpha(3)-isoforms const itutes less than or equal to 0.1% of the amount of alpha(1)-isoform at both the mRNA and protein level in rat kidney.