RS-127445, vehicle or other antagonists are pre-incubated with 240 μl of HEK-293 cells expressing the human 5-HT2B receptor suspension at 37 °C for 20 min. HEK-293 cells are incubated with[3H]-myoinositol (1.67 μCi/ml) in 162 cm
2 flasks overnight at 37 °C in an inositol free Ham's F12 medium containing 10% dialyzed foetal bovine serum. The cells are harvested, washed five times with phosphate bufffered saline and resuspended in inositol free Ham's F12 media at density of approximately 3×10
3 cells/ml. The reactions are initiated by addition of 5-HT. Sixty minutes later, the reactions are terminated by adding 50 μl of ice-cold 20% perchloric acid, chilled in an ice-water bath for 10 min and then neutralized with 160μl of 1 N KOH. Each sample is diluted with 2 ml of 50 mM Tris-HCl, pH 7.4 at room temperature. The aqueous portion (2.2 ml) is transferred onto Dowex AG1X8 columns (1 ml, 1 : 1, w/v) which has been washed with 5 ml of distilled water. The columns are then washed with 18 ml of distilled water and the inositol phosphates are eluted with 3 ml of 1 N HCl. The eluted radioactivity is determined by liquid scintillation spectroscopy using a Packard 1900CA analyzer.
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