Channel Properties of Nax Expressed in Neurons

Na x is a sodium-concentration ([Na + ])-sensitive Na channel with a gating threshold of ~150 mM for extracellular [Na + ] ([Na + ] o ) in vitro . We previously reported that Na x was preferentially expressed in the glial cells of sensory circumventricular organs including the subfornical organ, and was involved in [Na + ] sensing for the control of salt-intake behavior. Although Na x was also suggested to be expressed in the neurons of some brain regions including the amygdala and cerebral cortex, the channel properties of Na x have not yet been adequately characterized in neurons. We herein verified that Na x was expressed in neurons in the lateral amygdala of mice using an antibody that was newly generated against mouse Na x . To investigate the channel properties of Na x expressed in neurons, we established an inducible cell line of Na x using the mouse neuroblastoma cell line, Neuro-2a, which is endogenously devoid of the expression of Na x . Functional analyses of this cell line revealed that the [Na + ]-sensitivity of Na x in neuronal cells was similar to that expressed in glial cells. The cation selectivity sequence of the Na x channel in cations was revealed to be Na + ≈ Li + > Rb + > Cs + for the first time. Furthermore, we demonstrated that Na x bound to postsynaptic density protein 95 (PSD95) through its PSD95/Disc-large/ZO-1 (PDZ)-binding motif at the C-terminus in neurons. The interaction between Na x and PSD95 may be involved in promoting the surface expression of Na x channels because the depletion of endogenous PSD95 resulted in a decrease in Na x at the plasma membrane. These results indicated, for the first time, that Na x functions as a [Na + ]-sensitive Na channel in neurons as well as in glial cells.