title: A phospholipase C inhibitor, U-73122, blocks TSH-induced inositol trisphosphate production, Ca2+ increase and arachidonic acid release in FRTL-5 thyroid cells.
abstract: To characterize the role of phospholipase C (PLC)-mediated intrathyroid signal transduction by thyrotropin, we studied the effect of U-73122, an aminosteroid inhibitor of PLC-dependent activity, on TSH-activated PLC-Ca2+ and arachidonic acid (AA) signalling systems in cultured FRTL-5 rat thyroid cells. In the presence of extracellular Ca2+, TSH (0.1 microM) increased intracellular free calcium concentration ([Ca2+]i) by 63 +/- 6% with a sustained plateau phase, and AA release by 160 +/- 16%. By deletion of extracellular Ca2+, TSH induced a similar maximal [Ca2+]i increase, but the plateau phase and AA release were entirely suppressed. U-73122 (5 microM) inhibited TSH stimulation of 3H-labelled inositol trisphosphates (IP3) production by 73 +/- 3% (P < 0.01) in one study, and completely in another. U-73122 concentration-dependently blocked the TSH-induced Ca2+ increase in either the presence or absence of external Ca2+. U-73122 also showed a similar concentration-response inhibition of TSH-induced AA release. These results provide direct evidence of PLC mediation of TSH-stimulated signal transduction in FRTL-5 thyroid cells. TSH-induced external Ca2+ entry, as well as intracellular Ca2+ mobilization, is probably a PLC-mediated process. From an IP3-sensitive intracellular pool, TSH induces intracellular Ca2+ mobilization. External Ca2+ entry seems to be a prerequisite for TSH-induced AA release. U-73122 inhibition of both cytosolic Ca2+ increase and AA release further confirms [Ca2+]i dependence for TSH stimulation of AA release.
authors.affiliation: Department of Clinical Physiology, Walter Reed Army Institute of Research, Washington, DC 20307-5100.
authors.forename: X D
authors.initials: XD
authors.lastname: Wang
authors.forename: J G
authors.initials: JG
authors.lastname: Kiang
authors.forename: R C
authors.initials: RC
authors.lastname: Smallridge
mesh_terms: D000818:Animals; D016718:Arachidonic Acid / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism* / Q000494:pharmacology; D002460:Cell Line; D004963:Estrenes / Q000494:pharmacology*; D007295:Inositol Phosphates / Q000378:metabolism*; D011760:Pyrrolidinones / Q000494:pharmacology*; D051381:Rats; D015398:Signal Transduction; D013961:Thyroid Gland / Q000187:drug effects / Q000378:metabolism*; D013972:Thyrotropin / Q000494:pharmacology*; D010738:Type C Phospholipases / Q000037:antagonists & inhibitors* / Q000502:physiology
chemical_list: D004963:Estrenes; D007295:Inositol Phosphates; D011760:Pyrrolidinones; C060229:1-(6-((3-methoxyestra-1,3,5(10)-trien-17-yl)amino)hexyl)-1H-pyrrole-2,5-dione; D016718:Arachidonic Acid; D013972:Thyrotropin; D010738:Type C Phospholipases; D002118:Calcium