Previous electrophysiological and pharmacological studies on central and peripheral glia revealed the presence of voltage-gated Na channels with properties that are similar but not identical to those of neuronal Na channels. Here we report the isolation and characterization of a cDNA encoding the C-terminal portion of a putative glial Na-channel (Na-G) alpha subunit. The amino acid sequence deduced from this cDNA indicates that the Na-G represents a separate molecular class within the mammalian Na-channel multigene family. By Northern blot, RNase protection, and in situ hybridization assays, we demonstrate that, in addition to brain astroglia, the Na-G mRNA is expressed in cultures of Schwann cells derived from dorsal root ganglia or from sciatic nerve. In vivo, the Na-G mRNA is detected not only in brain, dorsal root ganglia, and sciatic nerve, but also in tissues outside the nervous system including cardiac and skeletal muscle and lung. Its level varies according to the tissue and is developmentally regulated. The sequence and expression data concur in designating Na-G as an distinct type of Na channel, presumably with low sensitivity to tetrodotoxin.