Depolarization exposes the voltage sensor of the sodium channels to the extracellular region

Summary Two domains of Na channels were mapped with site-specific antibodies raised in rabbit against synthetic peptides corresponding to a part of the voltage sensor of internal repeat 1C ₁⁺(amino acids 210–223) and to a region designated dipole (amino acids 1690–1699) of eel electroplax sodium channels. The antibodies bind to their respective domains in both purified and membrane-bound channels and immunoprecipitate the channels from eel electroplax and rat brain synaptosomes.Anti-C₁⁺depresses the action potential of rat sciatic nerve in a concentration-dependent way. It binds to the external side of rat brain synaptosomal vesicle, and its binding is potentiated by depolarization. Anti-dipole binds to the inner side of the vesicle, and the binding is inhibited by depolarization.We are most grateful to Dr. M.T. Tosteson (Harvard Medical School) for providing us with samples of the S₄IV peptides. We wish to express our gratitude to Drs. D. Gordon (Hebrew University) and A. Safran (The Weizmann Institute) for helping in the immunoprecipitation procedure, to Drs. H. Rahamimoff (Hebrew University) and A. Barzilai (Columbia University) for advising us with the vesicle experiments, to Drs. D. Kassel and M. Gavish (Technion) for many fruitful discussions, and to Dr. Y. Palti (Technion) for discussions of electric field and suggesting the dipole peptide. This work was supported by a basic research fund (BRF) of The Israel Academy of Sciences #430.87 (H.M. and G.S.), a BSF Grant #84-00367 (H.M.) and The Henry Gutwirt Fund for the Promotion of Research-Technion VPR Fund #184-0093 (H.M.).