Figure 1.

Loss of binding to cell-surface receptors following treatment with orthosteric and allosteric ligands. Binding was measured in transiently-transfected HEK-293 cells. (A) Cell surface receptor binding was assessed with the [³H]-NMS and (B) total receptor binding was assessed with [³H]-QNB as detailed in Methods. Surface binding was normalized to total receptor binding and expressed as % of control (no drug). Average receptor expression in untreated transiently transfected HEK cells was 325,000 sites/cell as measured by [³H]-NMS and 360,000 site/cell as measured by [³H]-QNB. Figure shows the mean results (± S.D.) from test compounds assayed in triplicate in a representative experiment repeated 2-6 times. Cell surface receptors remaining after treatment with each compound were as listed; No drug, 102% ± 13, carbachol, 45% ± 10, oxotremorine-M, 46% ± 8, pilocarpine, 65% ± 12, xanomeline, 69% ± 5, NDMC, 52% ± 10, AC-42, 60% ± 14, AC-260584, 55% ± 11. Statistically significant difference compared to no drug, * = p < 0.001, ** = p < 0.05 (Student t-test, Graph-Pad, Prism).