Figure 2.

Time course of agonist‐promoted internalisation of the β₃‐, β₂‐, and a β₃‐3232 chimeric adrenoceptor. HEK 293 cells stably expressing the β₂‐adrenoceptor, β₃‐adrenoceptor, or the β₃‐3232 (chimeric) were stimulated with 100 μM isoprenaline for the indicated times. Each of the constructs was tagged at their N‐terminus with a Myc‐tag allowing their immuno‐detection using an anti‐Myc antibody. Internalisation was assessed by flow cytometry and expressed as % loss of cell surface receptor immunoreactivity. Reproduced with permission from Angers (2003). The data show that in contrast to the β₂‐adrenoceptor that undergoes a time‐dependent internalisation upon isoprenaline stimulation, the β₃‐adrenoceptor does not. However, introducing the second intracellular loop and the carboxyl‐terminus of the β₂‐adrenoceptor within the β₃‐adrenoceptor backbone (β₃‐3232) restored agonist‐promoted internalisation to some extent