SUBCELLULAR-LOCALIZATION OF THE K+ CHANNEL SUBUNIT KV3.1B IN SELECTEDRAT CNS NEURONS

Voltage-gated potassium channels constitute the largest group of heter omeric ion channels discovered to date. Over 20 genes have been isolat ed, encoding different channel subunit proteins which form functional tetrameric K+ channels. We have analyzed the subcellular localization of subunit Kv3.1b, a member of the Kv3 (Shaw-like) subfamily, in rat b rain at the light and electron microscopic level, using immunocytochem ical detection. Detailed localization was carried out in specific neur ons of the neocortex, hippocampus and cerebellum. The identity of Kv3. 1b-positive neurons was established using double labeling with markers for specific neuronal populations. In the neocortex, the Kv3.1b subun it was expressed in most parvalbumin-containing bipolar, basket or cha ndelier cells, and in some bipolar or double bouquet neurons containin g calbindin. In the hippocampus, Kv3.1b was expressed in many parvalbu min-containing basket cells, as well as in calbindin-positive neurons in the stratum oriens, and in a small number of interneurons that did not stain for either parvalbumin or calbindin. Kv3.1b protein was not present in pyramidal cells in the neocortex and the hippocampus, but t hese cells were outlined by labeled presynaptic terminals from interne uron axons that surround the postsynaptic cell. In the cerebellar cort ex, granule cells were the only population expressing the channel prot ein. Careful examination of individual granule cells revealed a non-un iform distribution of Kv3.1 staining on the somata: circular bands of labeling were present in the vicinity of the axon hillock. In cortical and hippocampal interneurons, as well as in cerebellar granule cells, the Kv3.1b subunit was present in somatic and unmyelinated axonal mem branes and adjacent cytoplasm, as well as in the most proximal portion of dendritic processes, but not throughout most of the dendrite. Labe ling was also seen in the terminals of labeled axons, but not at a hig her concentration than in other parts of the axon. The distribution in the cells analyzed supports a role in action potential transmission b y regulating action potential duration. (C) 1997 Elsevier Science B.V.