Concentration and serum preincubation dependence of Ca
++ release by 5-HT and DOI in CHO cells expressing 5-HT
R (A, B) or 5-HT
R (C, D). Cells plated at 16,000 cells/well in 96-well plates for 24 hrs were either preincubated overnight in serum-free (open circles) or in serum-replete (closed circles) medium and loaded with Calcium 4. Peak height following stimulation was recorded for each well and normalized to the maximal response to 5-HT. n = 5-6; * p < 0.05, *** p < 0.001 vs. respective serum preincubation.