Apamin binding sites in human C6 cell line and their accessibility to monoclonal antibodies.

Apamin, a 18-amino acid bee venom toxic peptide specifically blocks a class of Ca(2+)-activated K+ channels. i) Mono 125I-iodoapamin binds to receptor sites in a human neuroglial cell line (C6 line) but not in human cell lines from pancreatic (RIN5F line) and colonic origin (HT29 line). ii) Receptor-bound apamin is still accessible to a large molecule since some anti-apamin monoclonal antibodies recognize apamin when bound to its receptor, both in intact cells of the human C6 glioma line and in rat brain synaptosomal membranes.