Cholinergic elements in a human choriocarcinoma cell line

Abstract Components of the cholinergic system have been identified in the JEG choriocarcinoma cell line. [ 3 H]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 × 10 7 M −1 min −1 , and dissociation, 4.2 × 10 −3 min −1 , revealed a dissociation constant ( K d ) 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 μ moles acetylcholine·min −1 ·(mg protein) −1 . No choline acetyltransferase activity was detected in these cells, however.