Differential expression of sodium channels in acutely isolated myelinating and non-myelinating Schwann cells of rabbits.

1. Single channel recordings were made of voltage-sensitive sodium channels in outside-out patches excised from the cell body region of Schwann cells. The cells were freshly isolated from sciatic nerves of 10-week-old rabbits and both myelinating and non-myelinating Schwann cells were visually identified for recordings. 2. Sodium channel activities were observed in approximately 75% of patches (n = 41) obtained from cell bodies of non-myelinating Schwann cells. In contrast, sodium channels were not observed in patches (n = 78) obtained from cell bodies of myelinating Schwann cells. 3. Transection of the sciatic nerves and allowing Wallerian degeneration to occur for 5-11 days in vivo prior to recording resulted in the appearance of sodium channel activities in approximately 30% of the patches (n = 33) obtained from the cell body of the myelinating cells. 4. It is interesting that although immunocytochemical and saxitoxin binding experiments indicate the clear presence of sodium channels in the plasmalemma of myelinating Schwann cells (both at the cell body and at the paranodal region), the present study suggests that these channels are absent from the soma region of normal myelinating Schwann cells.