Fixed cells were imaged by spinning disk confocal microscope (Nikon Ti Inverted microscope with Yokogawa confocal scanner unit CSU22) using a 60× objective or a Zeiss LSM 710 mounted on a Zeiss Axiovert Imager.Z2 using a 63× objective. Fluorescence intensities were quantified and analyzed using the computer program ImageJ (https://imagej.nih.gov/ij/). Images were saved as uncompressed 16-bit TIFF images, then loaded into ImageJ. Line scan analysis measured intensities along a manually drawn line across a cell plotted using the Plot Profile function on ImageJ. Data were exported to Microsoft Excel and plotted on line graphs. Lines were drawn such that they intercepted endosomes and ran across the length of the cell. To quantify endocytosis of the GCGR, colocalization was analyzed using EzColocalization ImageJ package (Stauffer et al., 2018 (link)). Cell outlines were manually drawn, and PCC between indicated channels was calculated. Mean PCC between samples was calculated and tested for statistical significance using a two tailed unpaired t test (GraphPad Prism).