ACTIVITY-DEPENDENT REGULATION OF NA+,K+-ATPASE ALPHA-ISOFORM MESSENGER-RNA EXPRESSION INVIVO

To investigate the functional role of the different Na+,K+-ATPase-alpha (catalytic) subunit isoforms in neuronal cells, we used quantitative in situ hybridization with riboprobes specific for alpha-1, alpha-2, and alpha-3 isoforms to measure the level of alpha-isoform-specific expression in the neuroendocrine cells of the supraoptic (SON) and paraventricular (PVN) nuclei of rat hypothalamus. A prolonged increase in electrical activity of these cells, achieved by 5 days of salt treatment, increased the amount of alpha-1 isoform mRNA in the SON and PVN by 50%. Levels of alpha-1 mRNA in other brain regions and levels of alpha-2 and alpha-3 mRNAs were not affected by salt treatment. We conclude that the alpha-1 isoform Na+,K+-ATPase may be specifically adapted to pump out Na+, which enters the cells through voltage-gated channels during neuronal depolarization.