Expression of Nav1.1 in rat retinal AII amacrine cells.

In retinal ganglion cells (RGCs), the expression of various types of voltage-gated sodium channel (Nav) alpha-subunits (Nav1.1, Nav1.2, Nav1.3, and Nav1.6) has been reported. Like RGCs, certain subsets of retinal amacrine cells, including AII amacrine cells, generate tetrodotoxin (TTX)-sensitive action potentials in response to light; however, the Nav subtypes expressed in these cells have not been identified. We examined the Nav subtypes expressed in rat retinal amacrine cells by in situ hybridization (ISH) using RNA probes specific for TTX-sensitive Na(v)s (Nav1.1, Nav1.2, Nav1.3, Nav1.6, and Nav1.7). Our results confirmed that Nav1.1, Nav1.2, Nav1.3, and Nav1.6 are localized in the ganglion cell layer (GCL). Interestingly, Nav1.1 was expressed not only in the GCL, but also in the inner nuclear layer (INL). The cell bodies of the Nav1.1-positive cells in the INL were located at the INL/inner plexiform layer (IPL) border. The cell bodies of AII amacrine cells are located close to the INL/IPL border, and these cells can be labeled with antibodies against parvalbumin (PV). Therefore, we combined ISH with immunohistochemistry and discovered that most of the PV-immunoreactive cells located at the INL/IPL border express Nav1.1. Our results show that AII amacrine cells express Nav1.1.