Measure arrestin signaling kinetics in real time with the live cell, fluorescent Borealis arrestin - Mu Opioid receptor (MOR) assay. Add the unmodified MOR and Borealis sensor to cells and measure robust signals the next day on an automated plate reader or fluorescence imaging system. This assay is genetically encoded and packaged in BacMam for efficient transduction in most cell types - including uniform and near 100% efficiency in HEK293 cells as well as expression in many primary or iPSC-derived cells. The kit includes the arrestin sensor BacMam, MOR BacMam, GRK2 BacMam, 500mM sodium butyrate in H2O, and a positive control receptor and agonist (AT1R BacMam and 5mM Angiotensin II in H2O). 10mL and 30mL sizes are available as well, as are Borealis kits for several other receptors. Other Montana Molecular tools including the cADDis cAMP sensor can be used alongside this assay.