Abstract

A detailed pharmacological characterization of the prostaglandin (PG) receptor coupled to phosphoinositide (PI) turnover and intracellular calcium mobilization in Swiss 3T3 mouse fibroblast cells was undertaken. The pharmacological profile of this functional receptor was compared with the pharmacological profile of specific [³H]PGF_{2 α} binding to bovine corpus luteum membranes, which are known to contain a bona fide FP receptor. PGs that were potent stimulators and full agonists in the PI turnover assay in the 3T3 cells were the following (for all, n = 3–45): 16-phenoxy-PGF_{2 α} (EC₅₀ = 0.61 ± 0.1 nM), cloprostenol (EC₅₀ = 0.73 ± 0.04 nM), 17-phenyl-PGF_{2 α} (EC₅₀ = 2.71 ± 0.35 nM), fluprostenol (EC₅₀ = 3.67 ± 0.61 nM), PhXA85 (EC₅₀ = 27.3 ± 5.63 nM) and PGF_{2 α} (EC₅₀ = 28.5 ± 5.26 nM). However, PGD₂ (EC₅₀ = 155 ± 29.9 nM;E _max = 49% of cloprostenol), PGE₂ (EC₅₀ = 2570 ± 566 nM;E _max = 59%) and U46619 (EC₅₀ = 1060 ± 310 nM; E _max = 63%) were less potent and were partial agonists, and iloprost and BW245C were inactive. Although the PGs tested exhibited lower affinities in the [³H]PGF_{2 α} binding assay than their functional potencies in the PI turnover assay, the rank orders of potencies and affinities were well correlated (r = 0.94; n = 15 compounds). However, the PI turnover assay was more sensitive than the calcium mobilization assay for rank ordering PG agonists. In conclusion, the Swiss 3T3 cells express an FP receptor coupled to PI turnover and intracellular Ca⁺⁺mobilization signal transduction pathways. The pharmacological profile of this receptor was similar to that of the FP receptor found in the bovine corpus luteum, a tissue previously used to clone the first pharmacologically defined FP receptor.