Subcellular localization of the voltage-gated potassium channels Kv3.1b and Kv3.3 in the cerebellar dentate nucleus of GAD67-GFP transgenic mice

Deep cerebellar dentate nuclei are in a key position to control motor planning as a result of an integration of cerebropontine inputs and hemispheric Purkinje neurons signals, and their influence through synaptic outputs onto extracerebellar hubs. GABAergic dentate neurons exhibit broader action potentials and slower afterhyperpolarization than non-GABAergic (presumably glutamatergic) neurons. Specific potassium channels may be involved in these distinct firing profiles, particularly, Kv3.1 and Kv3.3 subunits which rapidly activate at relatively positive potentials to support the generation of fast action potentials.
To investigate the subcellular localization of Kv3.1b and Kv3.3 in GAD- and GAD+ dentate neurons of GAD67-GFP (glutamic acid decarboxylase 67-green fluorescent protein) knock-in mice a pre-embedding immunocytochemical method for electron microscopy was used. Kv3.1b and Kv3.3 were in membranes of cell somata, dendrites, axons and synaptic terminals of both GAD- and GAD+ dentate neurons. The vast majority of GAD- somatodendritic membrane segments domains labeled for Kv3.1b and Kv3.3 (96.1% and 84.7%, respectively) whereas 56.2% and 69.8% of GAD- axonal membrane segments were immunopositive for these subunits. Furthermore, density of Kv3.1b immunoparticles was much higher in GAD- somatodendritic than axonal domains. As to GAD+ neurons, only 70.6% and 50% of somatodendritic membrane segments, and 53.3% and 59.5% of axonal membranes exhibited Kv3.1b and Kv3.3 labeling, respectively. In contrast to GAD- cells, GAD+ cells had a higher labeling density for both Kv3 subunits at their axonal than at their somatodendritic membranes.
Taken together, the distinct distribution of Kv3.1b and Kv3.3 potassium subunits could underlie the biophysical properties of dentate GAD- and GAD+ neurons.