Figure 2. Dependence of agonist-dependent and agonist-independent inositol phosphate formation on the receptor density.

HEK-293-FlpIn cells were transfected with increasing concentrations of the receptor cDNA indicated. After 24 h, cells were labelled with myo-[³H]inositol for 24 h. Inositol phosphate formation was determined in non-stimulated cells (●) and cells exposed to 1 μM PGF_2α for 15 min (○). Inositol phosphates were separated from inositol by chromatography as described in the caption of Figure 1. Parallel plates were used to determine the receptor density by binding of [³H]PGF_2α to intact cells. Unspecific binding was determined in the presence of 10 μM unlabelled PGF_2α. Values are means±S.E.M. for triplicate determinations for at least three independent experiments.