Interaction of the Na/HCO3 cotransporter SLC4A7 (NBCn1) and the N‐Methyl‐D‐Aspartate (NMDA) receptor subunit NR2A

Abstract

Intracellular pH affects neuronal excitability. We have previously demonstrated that the electroneutral Na/HCO3 cotransporter SLC4A7 (NBCn1) can interact with the PDZ protein PSD95, which is known to bind to NMDA receptors. In the present study, we examined the functional and physical association of NBCn1 and the NMDA receptor subunit NR2A. Human embryonic kidney (HEK) 293 cells were transiently transfected with NBCn1, NR1A/NR2A, and PSD95, and cell lysates were prepared. In immunoprecipitation with an antibody to PSD95, both NBCn1 and NR2A were detected in PSD95 immunoprecipitates. A parallel experiment using an antibody to NBCn1 showed the detection of PSD95 in NBCn1 immunoprecipitates. Immunofluorescence labeling of NBCn1 and NR2A showed both proteins colocalized on the plasma membranes of transfected HEK cells in the presence of PSD95. The colocalization decreased in the absence of PSD95. Two‐electrode voltage clamp was done to examine the functional effect of NBCn1/NR2A interaction on the NMDA receptors expressed in Xenopus oocytes. NBCn1 increased the peak glutamate current (at −40 mV) by 42% in the absence of CO2/HCO–3 and by 40% in the presence of CO2/HCO–3. However, the peak glutamate currents were unaffected during the pH recovery mediated by NBCn1. These data suggest that NBCn1 clusters with NMDA receptors via PSD95 and this clustering likely affects NMDA receptor expression and activity.