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 we applied competitive polymerase chain reaction (PCR) for estimation of mRNA in parenchymal zones of rat kidney for comparison to high-affinity [3H]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 < or = 0.1% of the amount of alpha 1-isoform at both the mRNA and protein level in rat kidney.