Differential Expression of Na , K - ATPase a ! and @ Subunit Isoforms at the Blood - Brain Barrier and the Choroid Plexus

The relative levels of expression of Na,K-ATPase a and j3 subunit isoforms were determined in rat cerebral microvessels, choroid plexus, and capillary-depleted brain homogenates by Western blot analysis. Three a (al, a2, as) and two j3 vl, B2) subunits were detected in brain as previously reported. All 3 a and 2 j3 isoforms were also found in microvessels. The choroid plexus expressed al, fll, and b2, while a2 and as were not found. Autoradiographic signals were normalized to a constant amount of protein from the 3 tissues to calculate relative levels of expression. Expression of al, az, and a3 was higher in microvessels than in the brain, by 1.7-, 1.2-, and 1.2-fold, respectively, but expression of fll and ,& was 5.5-fold lower. a1 was &fold higher in the choroid plexus than in the brain, while expression of B1 and B2 was 15and 5.5-fold lower, respectively. Na,K-ATPase enzymatic activities in microvessels and choroid plexus homogenates were similar and &fold lower than in brain homogenate. We conclude that: (a) expression of functionally active Na,K-ATPase isoenzymes in microvessels and choroid plexus is restricted in comparison to the brain possibly due to a limited pool of B1 and b2 subunits; ( b ) six structurally distinct Na,K-ATPase isoenzymes may be expressed in cerebral microvessels and two in the choroid plexus.