Regulation of Na+,K+-ATPase isoforms in rat neostriatum by dopamine and protein kinase C

Our previous studies showed that dopamine inhibits Na+,K+-ATPase activity in acutely dissociated neurons from striatum. In the present study, we have found that in this preparation, dopamine inhibited significantly (by similar to 25%) the activity of the alpha 3 and/or alpha 2 isoforms, but not the alpha 1 isoform, of Na+,K+-ATPase. Dopamine, via D1 receptors, activates cyclic AMP-dependent protein kinase (PKA) in striatal neurons. Dopamine is also known to activate the calcium- and phospholipid-dependent protein kinase (PKC) in a number of different cell types. The PKC activator phorbol 12,13-dibutyrate reduced the activity of Na+,K+-ATPase alpha 3 and/or alpha 2 isoforms (by similar to 30%) as well as the alpha 1 isoform (by similar to 15%). However, dopamine-mediated inhibition of Na+,K+-ATPase activity was unaffected by calphostin C, a PKC inhibitor. Dopamine did not affect the phosphorylation of Na+,K+-ATPase isoforms at the PKA-dependent phosphorylation site. Phorbol ester treatment did not alter the phosphorylation of alpha 2 or alpha 3 isoforms of Na+,K+-ATPase in neostriatal neurons but did increase the phosphorylation of the al isoform. Thus, in rat neostriatal neurons, treatment with either dopamine or PKC activators results in inhibition of the activity of specific (alpha 3 and/or alpha 2) isoforms of Na+,K+-ATPase, but this is not apparently mediated through direct phosphorylation of the enzyme. In addition, PKC is unlikely to mediate inhibition of rat Na+,K+-ATPase activity by dopamine in neostriatal neurons.