Fig. 3. Differences in agonist-stimulated phosphorylation of ß₁AR and ß₂AR in BHK cells. Untransfected cells and cells stably expressing ß₁AR or ß₂AR were incubated for 3 hours with [³²P]orthophosphate, incubated with or without 1 µM ISO for 15 minutes or the times indicated, washed and lysed. After solubilization, receptors were immunoprecipitated with antibodies to ß₁AR (BHK and BHK-hß₁ cells) or ß₂AR (BHK-hß₂ cells) and separated by SDS-PAGE. Receptor phosphorylation was detected on the dried gels and quantified by phosphor imaging as described in Materials and Methods. (A) A representative grayscale image of ³²P-labeled receptors from control and ISO-treated cells. Immunoprecipitates of equal amounts of protein (0.5 mg), ß₁AR (0.6 pmol) or ß₂AR (0.45 pmol) were loaded on the gel. (B) Summary of the quantification of receptor phosphorylation. Results are expressed as fold stimulation by agonist and are the means±s.e.m. of three separate experiments. (C) Time course of agonist-stimulated phosphorylation of ß₁AR () and ß₂AR () in BHK cells. Results shown are from a single experiment.