A novel CHOK1/tGFP-M1 cell line has been developed through stable transfection to modulate the internalization of the M1 receptor complex in living cells and to assay for compounds inducing tGFP-M1 distribution inside the cells. Fluorescent M1 cell line was obtained by transfection of an expression vector for a fusion protein of tGFP and human M1, as well as G418 into CHOK1 cells. Single cells with strong green fluorescence were selected by flow cytometry, and allowed to expand. These cells constitutively express the tGFP-M1 fusion protein. Assay Details: Innoprot M1 Internalizacion Assay Cell Line has been designed to assay compounds or analyze stimuli for their ability to modulate cholinergic receptor, muscarinic 1 internalization process following and quantifying the fluorescence distribution inside the cells. This highly reproducible assay allows monitoring CHRM1 receptor internalization process in High Content Analysis and fluorescence microscope applications.