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

Abstract

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.

Ouabain‐induced changes in MAP kinase phosphorylation in primary culture of rat cerebellar cells

“…In primary culture of rat cerebellar cells 1-μM ouabain inhibits about 30% of total Na,K-ATPase activity. 55 We conclude that observed effects are mediated either by the binding of ouabain to a small portion of the α1 subunit molecules or by complete inhibition of the α3 subunit.…”

“…Because of the fact that rat α3 subunit of Na,K‐ATPase is 3 orders of magnitude more sensitive to ouabain than α1 and its IC 50 is 6.7 ± 1.8 nM, while for α1 IC 50 is 48 ± 3.6 μM, 1‐μM ouabain almost completely inhibits the α3 subunit and only slightly inhibits the α1 subunit. In primary culture of rat cerebellar cells 1‐μM ouabain inhibits about 30% of total Na,K‐ATPase activity . We conclude that observed effects are mediated either by the binding of ouabain to a small portion of the α1 subunit molecules or by complete inhibition of the α3 subunit.…”

Cognitive deficits caused by a disease-mutation in the α3 Na+/K+-ATPase isoform

“…The NMDR has a well-documented role in the formation of several memories, including spatial, olfactory and contextual memory52. NMDA receptor expression was reduced by applying ouabain to cerebellar neurons53. Reduced NMDA receptor NR1 expression was described in homozygous E18 Myshkin mice, but not in heterozygous E18 and adult Myshkin mice26.…”

Na+/K+-pump and neurotransmitter membrane receptors

“…This effect is mediated by an increase in intracellular Ca 2+ . Thus, Na + /K + -ATPase and NMDAR can interact functionally by forming a macromolecular complex which can be important for restoring ionic balance after neuronal excitation (Akkuratov et al 2015). In addition, NMDAR function can be regulated by endogenous ouabain-like compounds.…”