title: Endothelin-1 stimulates the release of arachidonic acid and prostaglandins in cultured human ciliary muscle cells: activation of phospholipase A2.
abstract: In the present study we have examined the effects and mechanisms of endothelin-1 (ET-1) on arachidonic acid (AA) release and prostaglandin (PG) synthesis in human ciliary muscle (HCM) cells. ET-1 stimulated AA release in a time (t1/2=1.5 min) and concentration-dependent (EC50=5 nM) manner, which is primarily mediated through the ETA receptor subtype. The AA liberated by ET-1 appears to derive mainly from the phosphoinositides and phosphatidylcholine. Our data show that phospholipase A2 (PLA2), but not phospholipase C (PLC), plays an important role in ET-1-induced AA release. This conclusion is supported by the following findings: (1) ET-1-evoked AA release was inhibited by the PLA2 inhibitors dexamethasone, mepacrine and manoalide in a concentration-dependent manner. Conversion of AA into PGE2 was inhibited by the cyclooxygenase inhibitors in the following order: Indomethacin>naproxen >ibuprofen>NS-398>aspirin. (2) The phorbol ester, PDBu, an activator of protein kinase C, potentiated ET-1-induced AA release by 39%, but inhibited that of inositol phosphates formation by 62%. (3) Pretreatment of the labeled cells with isoproterenol lowered ET-1-induced inositol phosphates production, but had no effect on AA release. (4) U71322, a PLC inhibitor, inhibited ET-1-induced inositol phosphates production, but had no effect on that of AA release. (5) Pretreatment of the cells with pertussis toxin (0.1 microg ml-1) attenuated the stimulatory effects of ET-1 on AA release and PGE2 formation. These data demonstrate that ET-1 is a potent agonist for AA release and PG synthesis in HCM cells, and that PLA2, but not PLC, plays an important role in ET-1-induced AA release and PG synthesis. In ciliary muscle, AA and its metabolites play important roles in intracellular signalling, modulation of physiological processes, and regulation of intraocular pressure.
authors.affiliation: Department of Biochemistry and Molecular Biology, Medical College of Georgia, Augusta, GA 30912-2100, USA.
authors.forename: S Y
authors.initials: SY
authors.lastname: Yousufzai
authors.forename: A A
authors.initials: AA
authors.lastname: Abdel-latif
mesh_terms: D001095:Arachidonic Acids / Q000378:metabolism*; D002478:Cells, Cultured; D002924:Ciliary Body / Q000378:metabolism*; D016861:Cyclooxygenase Inhibitors / Q000494:pharmacology; D065128:Endothelin Receptor Antagonists; D019332:Endothelin-1 / Q000502:physiology*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D019204:GTP-Binding Proteins / Q000037:antagonists & inhibitors; D006801:Humans; D007295:Inositol Phosphates / Q000378:metabolism; D010739:Phospholipase D / Q000037:antagonists & inhibitors / Q000378:metabolism; D010741:Phospholipases A / Q000037:antagonists & inhibitors / Q000378:metabolism*; D054467:Phospholipases A2; D010743:Phospholipids / Q000378:metabolism; D011453:Prostaglandins / Q000378:metabolism*; D017466:Receptors, Endothelin / Q000502:physiology; D010738:Type C Phospholipases / Q000037:antagonists & inhibitors / Q000378:metabolism
chemical_list: D001095:Arachidonic Acids; D016861:Cyclooxygenase Inhibitors; D065128:Endothelin Receptor Antagonists; D019332:Endothelin-1; D004791:Enzyme Inhibitors; D007295:Inositol Phosphates; D010743:Phospholipids; D011453:Prostaglandins; D017466:Receptors, Endothelin; D010741:Phospholipases A; D054467:Phospholipases A2; D010738:Type C Phospholipases; D010739:Phospholipase D; D019204:GTP-Binding Proteins