Components of the cholinergic system have been identified in the JEG choriocarcinoma cell line. [3H]Quinuclidinyl benzilate (QNB) was used to identify high affinity muscarinic binding sites in a whole cell preparation. Specific binding was saturable with respect to QNB concentration and revealed a binding site density of 27 fmoles/mg protein. The bimolecular rates of association, 2.24 × 107 M-1 min-1, and dissociation, 4.2 × 10-3min-1, revealed a dissociation constant (Kd) of 180 pM which agreed closely with that derived from saturation isotherms, 245 pM. Muscarinic antagonists and agonists were able to compete effectively for these binding sites, whereas non-muscarinic compounds were not. Cholinesterase activity was also demonstrated with substrate preference consistent with that of acetyl-cholinesterase (acetylcholine > acetyl-β-methylcholine > butyrylcholine) hydrolyzing 2.42 ± 0.19 × 10-3 μmoles acetylcholine·min-1 ·(mg protein)-1. No choline acetyltransferase activity was detected in these cells, however.
ASJC Scopus subject areas