Functional Interaction Between Na/K-ATPase and NMDA Receptor in Cerebellar Neurons.

NMDA receptors play a crucial role in regulating synaptic plasticity and memory. Activation of NMDA receptors changes intracellular concentrations of Na(+) and K(+), which are subsequently restored by Na/K-ATPase. We used immunochemical and biochemical methods to elucidate the potential mechanisms of interaction between these two proteins. We observed that NMDA receptor and Na/K-ATPase interact with each other and this interaction was shown for both isoforms of α subunit (α1 and α3) of Na/K-ATPase expressed in neurons. Using Western blotting, we showed that long-term exposure of the primary culture of cerebellar neurons to nanomolar concentrations of ouabain (a cardiotonic steroid, a specific ligand of Na/K-ATPase) leads to a decrease in the levels of NMDA receptors which is likely mediated by the α3 subunit of Na/K-ATPase. We also observed a decrease in enzymatic activity of the α1 subunit of Na/K-ATPase caused by NMDA receptor activation. This effect is mediated by an increase in intracellular Ca(2+). Thus, Na/K-ATPase and NMDA receptor can interact functionally by forming a macromolecular complex which can be important for restoring ionic balance after neuronal excitation. Furthermore, this interaction suggests that NMDA receptor function can be regulated by endogenous cardiotonic steroids which recently have been found in cerebrospinal fluid or by pharmacological drugs affecting Na/K-ATPase function.