The K+ channel, Kv2.1, is apposed to astrocytic processes and is associated with inhibitory postsynaptic membranes in hippocampal and cortical principal neurons and inhibitory interneurons
Section snippets
Double immunostaining of Kv2.1 with parvalbumin, somatostatin and calbindin D28K
Adult Sprague–Dawley rats (Taconic, New York) were anaesthetized by volatile inhalation and perfused with ice-cold phosphate-buffered saline (PBS) followed by 4% paraformaldehyde in PBS, according to the NIH Animal Welfare Guidelines. The heads were decapitated and fixed overnight in 1% paraformaldehyde in PBS at 4°C. Serial sagittal sections (20 μm) of hippocampus and cortex were cut on a freezing microtome. Floating sections were incubated in a blocking solution of 10% normal goat serum, 0.2%
Kv2.1 expression in parvalbumin-, somatostatin-, calbindin D28K-immunoreactive interneurons
Previous studies have shown the Kv2.1 subunit to be expressed in the majority of principal neurons throughout the CNS including the hippocampus and cortex.7, 12, 19, 23The observation that the Kv2.1 protein was also widely expressed in presumed non-principal cells in the hippocampus and cortex, prompted us to first investigate Kv2.1 expression in defined populations of inhibitory interneurons in both the hippocampus and cortex. The calcium binding proteins, parvalbumin and calbindin D28K and
Discussion
The main findings of this study are: (1) Similar to the distribution in principal CNS neurons, Kv2.1 subunit protein is highly expressed across the somatodendritic axis of parvalbumin, somatostatin and calbindin D28K GABAergic inhibitory interneurons of the cortex and hippocampus. (2) Electron micrographs revealed that the distribution of Kv2.1 subunits on the plasma membrane of somata and proximal dendrites of both principal neurons and inhibitory interneurons was neither homogeneous nor
Conclusions
We have described that the dendritic expression of Kv2.1 subunits in principal neurons and inhibitory interneurons is not random across the somatodendritic axis but is specifically associated with intracellular subsurface cisterns and extracellularly with plasma membranes apposed to astrocytic processes. The clustered expression of Kv2.1 subunits on neuronal membranes adjacent to astrocytic processes strongly argues that K+ released into the extracellular space through these channels will be
Acknowledgements
The authors would like to thank Drs Mark Mayer and Vittorio Gallo for their comments on the manuscript.
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Both authors contributed equally to this study.