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 important to know whether the alpha(2)- or alpha(3)-isoform of Na-K-adenosinetriphosphatase (Na-K-ATPase) is expressed in mammalian kidney in addition to the predominant alpha(1) beta(1)-isozyme. Here me applied competitive polymerase chain reaction (PCR) for estimation of mRNA in parenchymal zones of rat kidney for comparison to high-affinity [H-3]ouabain binding. The alpha(3)-isoform mRNA was demonstrated to form 0.04-0.05% 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 isozyme 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 constitutes less than or equal to 0.1% of the amount of alpha(1)-isoform at both the mRNA and protein level in rat kidney.