POLYSIALIC ACID IS ASSOCIATED WITH SODIUM-CHANNELS AND THE NEURAL CELL-ADHESION MOLECULE N-CAM IN ADULT-RAT BRAIN

We have studied alpha-2,8-linked polysialic acid (polySia) and the neural cell adhesion molecule (N-CAM in the adult rat brain by immunohistochemistry and Western blot analysis. Both molecules were widely distributed but not ubiquitous. Various brain regions showed colocalization of polySia and. N-CAM. Strong immunoreactivity for polySia was seen in regions which were negative for N-CAM, such as the main and accessory olfactory bulbs. Immunohistochemical evidence for the heterogeneity of polySia expression in different brain regions was confirmed by immunoblotting. We present evidence that N-CAM is not the only polySia bearing protein in adult rat brain. Specifically, immunoprecipitation using the polysia-specific monoclonal antibody mAb 735 precipitated not only N-CAM isoforms carrying polySia, but also the sodium channel alpha-subunit. Immunoblotting using sodium channel alpha-subunit antibody (SP20) revealed a smear from 250 kDa upwards. PolySia removal using an endoneuraminidase specific for alpha-2,8-linked polysialic acid of 8 or more residues long, reduced this smear to a single band at 250 kDa. Thus both N-CAM and sodium channels carry homopolymers of alpha-2,8-linked polysialic acid in adult rat brain.