Figure 4.

The effect of isoproterenol and EGF on the cellular distribution of epitope-tagged β₂ ARs and EGFR–GFP. Confocal microscopic images depicting the cellular distribution of HA-tagged β₂ AR (a, d, and g), and EGFR–GFP (23) (b, e, and h) before (NS; a–c) and after 30 min exposure to isoproterenol (d–f) or EGF (g, h, and i) in 293 cells. In the absence of agonist, both β₂ AR and EGFR-GFP staining was predominantly confined to the plasma membrane (c). After exposure to isoproterenol, a portion of both receptor pools redistributed to an intracellular compartment (f). After exposure to EGF, redistribution of the EGFR–GFP, but not the β₂ AR, was observed (i). Qualitatively similar results have been obtained in COS-7 cells.