NON-SELECTIVITY OF THE MONOCLONAL-ANTIBODY M35 FOR SUBTYPES OF MUSCARINIC ACETYLCHOLINE-RECEPTORS

The monoclonal antibody M35, one of the first monoclonal antibodies su ccessfully raised against muscarinic acetylcholine receptors, has been widely used to study the distribution of this protein in a variety of tissues and cell types of different species. It is not fully known, h owever, to which muscarinic acetylcholine receptor subtypes M35 binds. Knowledge of subtype-selectivity of M35 is a necessary step towards a functional interpretation of the obtained immunocytochemical data. Th e aim of the present study was to determine the subtype-selectivity of M35 employing transfected CHO-K1 cells stably expressing human m1-m5 muscarinic acetylcholine receptors separately, and to study M35 immuno reactivity in areas of rat central and peripheral tissues known to be specifically enriched in a single muscarinic acetylcholine receptor su btype. The results show that (a) all five transfected cell lines were immunopositive for M35, (b) nontransfected control cells were immunone gative, (c) the number of mAChRs expressed per cell correlated positiv ely with the intensity of M35 immunoreactivity, and (d) cell types in aldehyde-fixed rat tissue enriched in a single m1-m4 subtypes revealed clear M35 immunoreactivity. Taken together, the present results show that M35 does not discriminate between muscarinic acetylcholine recept or subtypes. Evidently, the epitope of M35 on the receptor-protein is preserved on all muscarinic acetylcholine receptor subtypes. The epito pe for M35 must, therefore, be localized on a homologous part of each subtype. (C) 1997 Elsevier Science Inc.