Immunolocalization of sodium channel isoform NaCh6 in the nervous system

Sodium channel 6 (NaChG) is the alpha-subunit of a voltage-gated sodium cha nnel expressed in the rat nervous system. The mRNA for this isoform has bee n shown to be expressed in both neuronal and glial cells by in situ hybridi zation. To examine localization of NaChG protein, polyclonal antibodies spe cific for NaChG were generated against peptides from two cytoplasmic domain s and a fusion protein from an extracellular domain. Affinity-purified anti bodies were used to localize NaChG in the brain, spinal cord, peripheral ne rvous system, and neuromuscular junction. There was widespread labeling of neurons in the brain and spinal cord. NaChG was present in both sensory and motor pathways. Radial glial cells in the cerebellum were intensely labele d for both GFAP and NaChG. At the subcellular level, NaChG is found in axon s, dendrites, and the cell body. Motor neurons and primary sensory neurons in dorsal root ganglia had strong cytoplasmic and axonal staining. Nodes of Ranvier in peripheral nerve and in the spinal cord were also intensely lab eled. Motor neuron axons near the neuromuscular junction were labeled up to , but not including, terminal boutons. Dendrites of pyramidal cells in the cortex, hippocampus, and cerebellum were labeled. NaChG is the first NaCh s ubtype to be localized either at the node of Ranvier or to a dendrite. We c onclude that NaChG is widely distributed in the central and peripheral nerv ous systems and is likely to be important for the electrical properties of the axon and dendrite. J. Comp. Neurol. 420:70-83, 2000. (C) 2000 Wiley-Lis s, Inc.