Figure 4.

Agonist-mediated internalization of receptors in cells coexpressing κ-β₂ or δ-β₂ receptors. Cells were treated with indicated concentrations of 100 μM isoproterenol for 60 min at 37°C, stained, and analyzed by ELISA as described under Materials and Methods. The mean absorbance without agonist treatment is taken as 100%. Significant differences from untreated controls are indicated. **, P < 0.01, ***, P < 0.005 (n = 3–5).