The distributions of isoforms of the Na,K-ATPase a subunit were determined in mature cultured hippocampal neurons and in a polarized epithelial cell line. We find that hippocampal neurons express the α1 and α3 isoforms in the membranes of both axons and dendrites. In contrast the al and α3 proteins are exclusively basolateral when expressed endogenously or by stable transfection in renal epithelial cells. These data suggest that epithelial cells and hippocampal neurons localize these proteins by different mechanisms. These observations contrast with those made for the vesicular stomatitis virus and the influenza glycoproteins, which are polarized in both epithelial and neuronal cells.
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