ANTIBODIES TO POTASSIUM CHANNELS OF PC12 IN SERUM OF ISAACS SYNDROME - WESTERN-BLOT AND IMMUNOHISTOCHEMICAL STUDIES

We investigated the pathophysiology of nerve hyperexcitability in a pa tient with Isaacs' syndrome, who had typical clinical and electromyogr aphic features and responded to plasma exchange. Immunoblotting and im munohistochemistry studies showed that antibodies from this patient re acted with the lysate of a neuronal cell line (PC12). In Western blots , constituents of the patient's serum, particularly immunoglobulin M, reacted with proteins of approximately 50 and 18 kDa, whereas the cont rol serum did not. A cross-linking study with alpha-dendrotoxin (7 kDa ) showed a 57 kDa protein-peptide complex. Immunohistochemistry showed that the patient's serum reacted with PC12 cells and human intramuscu lar nerve axons. Our findings indicate that in Isaac's syndrome nerve hyperexcitability is the result of the immunological involvement of th e voltage-dependent potassium channels located along the distal motor nerve or at the nerve terminal. (C) 1997 John Wiley & Sons, Inc.