The endogenous pentapeptide QYNAD induces acute conduction block in the isolated rat sciatic nerve

Reversible block of sodium channels by endogenous substances was claimed to account for the fast relapses and remissions seen in demyelinating autoimmune disorders. The pentapeptide QYNAD, isolated from the cerebrospinal fluid from patients with multiple sclerosis (MS), blocked Na+ channels in various types of cultured cells. We show that 100 muM QYNAD bath-applied to isolated rat sciatic nerve causes the amplitude and area of the compound nerve action potential to decrease by 30-40%, while the latency increases. Wash-out reverses the changes in part. This suggests that QYNAD may indeed contribute to the fast symptom changes in MS and related diseases. (C) 2002 Elsevier Science Ireland Ltd. All rights reserved.