I have GPCRs from transfected CHO for binding assays. The problem is that it no longer couples to G-protein or inhibits c-AMP, but the antibody says that the receptor is highly expressed on the cell surface.
What could be a problem with the GPCRs that explain it?
I would appreciate any help.

did you check whether you had any problems checking the cAMP levels? I mean , it may be possible that something is wrong with cAMP assay