Importance of arachidonic acid metabolites in regulating ATP-induced calcium fluxes in thyroid FRTL-5 cells.
Stimulating rat thyroid FRTL-5 cells with the purinergic agonist ATP activates both the inositol phosphate signal-transduction pathway and the phospholipase A2 pathway. In the present study we wanted to investigate the possible inter-relationships between these two systems during ATP-induced changes in intracellular free calcium ([Ca2+]i). Pretreatment of Fura-2 loaded cells with 4-bromophenylacyl, an inhibitor of phospholipase A2, had no effect on the ATP-induced entry of Ca2+ but inhibited the release of sequestered Ca2+. Nordihydroguaiaretic acid (NDGA), a lipoxygenase inhibitor, and 5,8,11,14-eicosatetraynoic acid (ETYA), an inhibitor of cytochrome P-450 enzymes, attenuated the ATP-evoked transient increase in [Ca2+]i. Furthermore, the capacitative entry of Ca2+ was also attenuated in NDGA- and ETYA-treated cells stimulated with ATP. Similar results were obtained using econazole, an inhibitor of cytochrome P-450 enzymes. However, treatment of the cells with indomethacin, a cyclooxygenase inhibitor, had no effect on the ATP-evoked response in [Ca2+]i. We also showed that stimulation of intact or permeabilized FRTL-5 cells with arachidonic acid released sequestered calcium. This calcium originated, at least in part, from an IP3 sensitive calcium pool. In addition, arachidonic acid rapidly acidified the cytosol. The results suggest that metabolism of arachidonic acid by a non-cyclooxygenase pathway is of importance in supporting agonist-induced calcium fluxes evoked via stimulation of the inositol phosphate pathway in FRTL-5 cells. Furthermore, arachidonic acid per se may modify agonist-induced calcium fluxes in these cells.
Törnquist
K
K
Department of Zoology, University of Helsinki, Finland.
Ekokoski
E
E
Forss
L
L
Matsson
M
M
D015117:5,8,11,14-Eicosatetraynoic Acid / Q000494:pharmacology; D000255:Adenosine Triphosphate / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D000818:Animals; D016718:Arachidonic Acid / Q000378:metabolism* / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002460:Cell Line; D004464:Econazole / Q000494:pharmacology; D007295:Inositol Phosphates / Q000378:metabolism*; D009637:Masoprocol / Q000494:pharmacology; D010741:Phospholipases A / Q000037:antagonists & inhibitors / Q000378:metabolism*; D054467:Phospholipases A2; D051381:Rats; D015398:Signal Transduction; D013961:Thyroid Gland / Q000166:cytology / Q000378:metabolism*
D007295:Inositol Phosphates; D015117:5,8,11,14-Eicosatetraynoic Acid; D016718:Arachidonic Acid; D004464:Econazole; D009637:Masoprocol; D000255:Adenosine Triphosphate; D010741:Phospholipases A; D054467:Phospholipases A2; D002118:Calcium