Compartmentalization of Ca(2+) between dendritic spines and shafts is governed by
diffusion barriers and a range of Ca(2+) extrusion mechanisms. The distinct contribution
of different Ca(2+) clearance systems to Ca(2+) compartmentalization in dendritic
spines versus shafts remains elusive. We applied a combination of ultrastructural
and functional imaging methods to assess the subcellular distribution and role of
NCX1 in rat CA1 pyramidal cells. Quantitative electron microscopic analysis of preembedding
immunogold reactions revealed uniform densities of NCX1 along the shafts of apical
and basal dendrites, but densities in dendritic shafts were approximately seven times
higher than in dendritic spines. In line with these results, two-photon imaging of
synaptically activated Ca(2+) transients during NCX blockade showed preferential action
localized to the dendritic shafts for NCXs in regulating spine-dendrite coupling.
