Monoclonal rat anti-Torpedo electroplax nicotinic acetylcholine receptor antibodies: immunochemical characterization.

The interaction of Torpedo californica nicotinic acetylcholine receptor (nAcChoR) with three rat monoclonal antibodies (mcab) directed against nAcChoR (Gomez et al., 1979) was studied by use of four different radioimmunoassay protocols. Each mcab reacts poorly with formalin-fixed Staphylococcus aureus or S. aureus Protein A, which requires that an additional incubation with second antibody (goat anti-rat immunoglobulin G) is included in each radioimmunoassay paradigm. One mcab inhibits 125I-labeled alpha-bungarotoxin binding to nAcChoR, recognizes a subset of solubilized nAcChoR-toxin complexes, and shows higher titer against nAcChoR in the absence of toxin. Thus, it appears to be directed against nAcChoR antigenic determinants that at least partially overlap with toxin binding sites. Two other mcab react with nAcChoR in a toxin-independent manner. Receptor-mcab dissociation constants are less than 10 nM, according to each assay paradigm. Estimates of antibody titer or concentrations of antibody in stock hybridoma supernatants vary according to the assay used. This predictable result is attributed to differences in design and sensitivity of assay protocols. The data provide a basis for further utilization of monospecific antibodies as probes in characterization of nAcChoR structure and function.