CHARACTERIZATION OF MUSCARINIC ACETYLCHOLINE-RECEPTORS IN CULTURED ADULT SKIN FIBROBLASTS - EFFECTS OF THE SWEDISH ALZHEIMERS-DISEASE APP-670 671 MUTATION ON BINDING LEVELS/

We have characterised the muscarinic receptor subtypes found in human skin fibroblasts and compared binding levels in cell lines from member s of the Alzheimer's disease family with the Swedish amyloid precursor protein (APP) 670/671 mutation. Binding studies with [H-3] quinuclidi nyl benzilate ([H-3]QNB) and the M2/M4 selective antagonist -dihydro-1 1-{[(2-[(di-propylamino)methyl]-1-piperi dinyl}ethyl)amino]carbonyl]-6 H-pyrido (2,3-b)(1,4)benzodiazepine-6-one ([H-3]AF-DX 384) revealed th e presence of a single population of muscarinic receptors on lysed fib roblast membranes. [H-3]QNB binding was displaced by a number of selec tive muscarinic ligands with a rank order of potency: atropine > himba cine > methoctramine > (+/-)-p-fluoro-hexahydro-sila-difenidol hydroch loride > pirenzepine > muscarinic-toxin-3. APP 670/671 mutation carryi ng cell lines showed 25-35% lower levels of muscarinic receptors label led with [H-3]QNB, [H-3]N-methyl scopolamine and [H-3]AF-DX 384, compa red to controls. This difference was not statistically significant due to large individual variation. It is concluded that muscarinic recept ors on adult skin fibroblasts are predominantly of the M2 subtype. Sin ce these cells do not possess M1 and M3 receptor subtypes, they are un likely to provide a good model for studying muscarinic receptor regula tion of APP processing.