CHO Cell Lines for Receptor Studies

All experiments were conducted using intact cells or membranes prepared from Chinese hamster ovary (CHO) cells stably transfected with either human cannabinoid type-1 receptors (CHO-hCB1), human cannabinoid type-2 receptors (CHO-hCB2) (Shoemaker et al., 2005 (link)), or human mu opioid receptors (CHO-hMOR) (Seely et al., 2012 (link)). CHO-hCB1 cells were purchased from DiscoverRx Corporation (Fremont, CA, USA) and cultured in HAM’s F-12 K media (ATCC, Manassas, VA, USA). CHO-hCB2 and CHO-hMOR cells were cultured in DMEM (Mediatech Inc., Manassas, VA, USA). All media contained 10% Fetalplex, (Gemini Bioproducts, Sacramento, CA, USA), 0.05 IU/mL penicillin, 50 μg/mL streptomycin (Invitrogen, Carlsbad, CA, USA), and 250 μg/mL of Geneticin (G418; Sigma-Aldrich, St. Louis, MO, USA). Cells were cultured in a 37°C humidified incubator with 5% CO₂ and harvested with PBS (10 mM)/EDTA (1 mM) when 80% confluent. All cells used were maintained between passages 4–15.