Abstract
An FP prostaglandin (PG) receptor on the A7r5 rat aorta smooth muscle cell line has been characterized by assays of phosphoinositide (PI) turnover and intracellular calcium mobilization stimulated by structurally diverse PGs. In the PI turnover assay, cloprostenol was the most potent PG tested, with a potency (EC50) of 0.84 ± 0.06 nM (mean ± S.E.M., n = 34), and was a full agonist. Other known FP receptor agonists tested in this assay had efficacies ≥85% of the cloprostenol value and high potencies: 16-phenoxy PGF2α (2.05 ± 0.19 nM), 17-phenyl PGF2α (2.80 ± 0.59 nM), fluprostenol (4.45 ± 0.19 nM), PGF2α (30.9 ± 2.82 nM) and PhXA85 (43.5 ± 11.4 nM). Other classes of PGs evaluated (PGD2, enprostil, 17-phenyl PGE2, PGE2, sulprostone and U-46619) were less potent and less efficacious than the FP receptor agonists, or were inactive. For a large group of standard PGs evaluated in the PI turnover assay, both potencies and efficacies correlated well with those reported for the FP receptor of Swiss mouse 3T3 fibroblasts. The potencies of fluprostenol and PGF2α as stimuli of intracellular calcium mobilization matched well their potencies in the PI turnover assay, but fluprostenol had twice the efficacy of PGF2α. Both signaling responses stimulated by fluprostenol were significantly inhibited by U73122, a selective inhibitor of phosphoinositide turnover (IC50 = 1.25 ± 0.16 μM for PI turnover), and by chelation of calcium in the medium. Together with the PI turnover data, these studies of intracellular calcium mobilization linked to activation of the FP receptor, provide additional characterization of the pharmacological properties of this receptor.
Footnotes
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Send reprint requests to: Dr. Brenda W. Griffin, Molecular Pharmacology Unit, Alcon Laboratories, Inc. R2-43, 6201 South Freeway, Fort Worth, TX 76134.
- Abbreviations:
- FP receptor
- prostaglandin PGF2αreceptor
- PG
- prostaglandin
- DMEM
- Dulbecco’s modified Eagle medium
- [3H]-IPs
- [3H]-inositol phosphates
- EDTA
- ethylene diamine tetraacetic acid
- EGTA
- ethylene glycol-O,O′-bis(2-amino ethyl)-N,N,N′,N′-tetraacetic acid)
- AVP
- [Arg8]-Vasopressin
- HEPES
- N-2-hydroxyethylpiperazine-N′-2-ethane sulfonic acid
- PI
- phosphoinositide
- PLC
- phospholipase C
- IC50
- concentration inhibiting response by 50%
- EC50
- concentration producing half-maximal response
- Emax
- maximal response (%), relative to the maximal response of standard agonist
- Received November 19, 1997.
- Accepted March 16, 1998.
- The American Society for Pharmacology and Experimental Therapeutics
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