Figure 4
Chronic EPI, but not NE, treatment desensitizes the β 2 -AR signal in SHβ 2 AR4 cells. SHβ2AR4 cells were treated for 16–24 hr with the vehicle (ascorbate, 1 μM), EPI (300 nM), NE (1 μM), EPI + Prop (30 nM), or Prop (30 nM) alone. Intact cells were assessed for ISO-stimulated (250 nM) cAMP accumulation. Chronic 300 nM EPI (n = 6; *P < 0.05), but not 1 μM NE (n = 3), pretreatment desensitized the β-AR response to ISO compared to the corresponding vehicle-treated control. The β-AR antagonist propranolol blocked EPI-induced β2-AR desensitization. Data represent mean ± S.E. of at least 3 independent determinations; comparisons were made by ANOVA with Dunnett's post-hoc test.