Ligand concentration and serum preincubation dependence on ERK activation in 5-HT
R- and 5-HT
R-CHO cells. 5-HT2AR- (A and B) and 5-HT2CR-CHO (C and D) cells plated at 16,000 cells/well for 24 hrs were preincubated in serum-replete medium (closed circles) or serum-free medium (open circles) overnight, followed by stimulation with vehicle (PBS) or indicated concentrations of 5-HT or DOI for 5 min. Levels of pERK were determined by plate immunoassay and normalized to cell number with crystal violet staining. Points represent data combined from three independent experiments (n = 5-6/experiment) normalized to vehicle control. * p < .05, ** p < 0.001 vs. vehicle.