Figure 5
Chronic 300 nM EPI down-regulates α 2A -AR in β 2 -AR-transfected, but not native, SH-SY5Y cells. Wt SH-SY5Y or SHβ2AR4 cells were incubated for 16–24 hr with vehicle (ascorbate, 0.1 mM), 1 μM NE, 300 nM EPI, EPI + Propranolol (30 nM), or 30 nM Propranolol alone. Cell membrane homogenates were generated as described in Methods. Specific binding (8084 ± 609 cpm/mg protein in vehicle-treated cells) was calculated by subtracting the binding of a single concentration of radioligand (2 nM) in the presence of phentolamine (10 μM) from the binding in its absence. Unlike in native cells, chronic EPI treatment reduced α2A-AR levels as compared to vehicle (*p < 0.05); inclusion of propranolol blocked the EPI-induced α2A-AR down-regulation (#p < 0.05 as compared to EPI treatment) in SHβ2AR4 cells. Data represent mean ± S.E., n = 2–4; comparisons were made by ANOVA with Tukey's post-hoc test.