Uptake assays

HEK-293 Flp-In cells (Invitrogen, Carlsbad, CA) stably overexpressing human or mouse OCT3 were generated, maintained, and used for uptake assays as previously described [37]. For comparison between human OCT3 and mouse Oct3 NE uptake kinetics (Fig 2E), uptake time was 2 minutes at 37°C. K_m and V_max were calculated by fitting the data to Michaelis-Menten equations using GraphPad Prism software (La Jolla, CA). For [³H]-NE uptake in primary adipocytes, the same procedures were performed as described above.