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D. Van Der List, J. S. Trimmer, L. M. Chalupa; Organization of the IPL in the Adult Mouse Retina Is Defined by Distinct Expression Patterns of Voltage-Gated Potassium Channel Subunits. Invest. Ophthalmol. Vis. Sci. 2008;49(13):5807. doi: https://doi.org/.
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Voltage-gated potassium or Kv channels play diverse roles in regulating neuronal excitability. Their discrete subcellular localization at precise locations on somata, dendrites, axons and presynaptic terminals impacts local signaling events and shapes the function of neural networks. Here we used well-characterized monoclonal antibodies against specific Kv subunits to define the subcellular localization of Kv channels in the IPL of the adult mouse.
Immunohistochemical and fluorescent imaging techniques were used to define the localization of Kv channels in the IPL of the adult mouse. Sections were taken from the center of the eye passing through the optic nerve and labeled with monoclonal antibodies to Kv subunits, (10micrograms/ml; NeuroMab, Davis, CA), rabbit anti-calretinin, (1:500, Swant, Bellinzona, Switzerland); and goat anti-choline acetyltransferase (ChAT; 1:50; Chemicon, Temecula, CA). Secondary antibodies were conjugated to Alexa 488, or Alexa 594 (1:500; Molecular Probes, Eugene, OR). Images were acquired on an Olympus FV500 confocal microscope (Tokyo, Japan).
We find that Kv1.1, Kv1.4 and Kvβ1.1 subunits co-localize in three narrow bands that interdigitate with calretinin and ChAT labeled processes. These Kv expressing bands appear to correspond to strata 1, 3 and 5 of the IPL. These subunits would be expected to form fast inactivating low threshold Kv channels, regulating transmitter release from presynaptic terminals located at these sites. Also expressed in these bands are Kv4.2, Kv4.3 and KChIP1 subunits expected to form fast inactivating subthreshold Kv channels on dendrites. We also find that Kv2.1 and Kv3.1 subunits are interdigitated with the bands containing the Kv1 and Kv4 subunits. These correspond to the calretinin and ChAT positive strata 2 and 4. A previous study showed Kv3.1 expression at these sites in dendrites of starburst amacrine cells (Ozaita et al., J Neurosci 24:7335, 2004), and Kv2.1 may share a similar localization.
Collectively, our findings suggest that distinct Kv channel-mediated regulation of excitability occurs in different strata of the IPL. These results also provide new molecular markers for the strata of the IPL as well as new targets for studies aimed at defining the molecular determinants of synaptic transmission in the adult mouse retina.
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