The exact location of an ion channel on the axo-somato-dendritic surface of a nerve
cell crucially affects its functional impact. Recent high-resolution immunolocalization
experiments examining the distribution of GABA and glutamate receptors, voltage-gated
potassium and sodium channels and hyperpolarization-activated mixed cation (HCN) channels
clearly demonstrate the lack of simple rules concerning their subcellular distribution.
For example, the density of HCN1 subunits in pyramidal cells increases 60-fold from
soma to distal dendrites but is uniform over the somato-dendritic surface of olfactory
bulb external tufted cells and is highest in the axon of cortical and cerebellar basket
cells. Such findings highlight the necessity of determining the precise subcellular
location and density of each ion channel in every cell type. Here, I suggest that
variations in the subcellular distribution of ion channels are previously unrecognized
means of increasing neuronal diversity and, thus, the computational power of the brain.
