Cellular and subcellular localization of Na+–Ca2+ exchanger protein isoforms, NCX1, NCX2, and NCX3 in cerebral cortex and hippocampus of adult rat

Na+–Ca2+ exchanger (NCX) controls cytosolic Ca2+ and Na+ concentrations ([Ca2+]i and [Na+]i) in eukaryotic cells. Here we investigated by immunocytochemistry the cellular and subcellular localization of the three known NCX isoforms, NCX1, NCX2 and NCX3, in adult rat neocortex and hippocampus. NCX1–3 were widely expressed in both brain areas: NCX1 immunoreactivity (ir) was exclusively associated to neuropilar puncta, while NCX2–3 were also detected in neuronal somata and dendrites. NCX1–3 ir was often identified around blood vessels. In both neocortex and hippocampus, all NCX isoforms were prominently expressed in dendrites and dendritic spines contacted by asymmetric axon terminals, whereas they were poorly expressed in presynaptic boutons. In addition, NCX1–3 ir was detected in astrocytes, notably in distal processes ensheathing excitatory synapses. All NCXs were expressed in perivascular astrocytic endfeet and endothelial cells.The robust expression of NCX1–3 in heterogeneous cell types in the brain in situ emphasizes their role in handling Ca2+ and Na+ in both excitable and non-excitable cells. Perisynaptic localization of NCX1–3 in dendrites and spines indicates that all isoforms are favourably located for buffering [Ca2+]i in excitatory postsynaptic sites. NCX1–3 expressed in perisynaptic glial processes may participate in shaping astrocytic [Ca2+]i transients evoked by ongoing synaptic activity.