Cloning of a sodium channel α subunit from rabbit Schwann cells

Overlapping cDNA clones spanning the entire coding region of a Na-channel α subunit were isolated from cultured Schwann cells from rabbits. The coding region predicts a polypeptide (Na(s)) of 1984 amino acids exhibiting several features characteristic of Na-channel α subunits isolated from other tissues. Sequence comparisons showed that the Na(s) α subunit resembles most the family of Na channels isolated from brain (≃80% amino acid identity) and is least similar (≃55% amino acid identity) to the atypical Na channel expressed in human heart and the partial rat cDNA, NaG. As for the brain II and III isoforms, two variants of Na(s) exist that appear tu arise by alternative splicing. The results of reverse transcriptase-polymerase chain reaction experiments suggest that expression of Na(s) transcripts is restricted to cells in the peripheral and central nervous systems. Expression was detected in cultured Schwann cells, sciatic nerve, brain, and spinal cord but not in skeletal or cardiac muscle, liver, kidney, or lung.