title: Calcium release from porcine thyroid microsomes by phosphatidylinositol 4,5-bisphosphate and inositol 1,4,5-trisphosphate.
abstract: We have demonstrated Ca2+ mobilization induced by inositol compounds from intracellular stores of isolated porcine thyroid cells that were permeabilized with saponin and from fractionated thyroid microsomes that were preloaded with Ca2+. In the presence of saponin and antimycin A, a mitochondrial inhibitor, the Ca2+ concentration in the cell suspension decreased after the addition of ATP; the addition of inositol 1,4,5-trisphosphate (IP3) elicited transient elevations in Ca2+. The half-effective concentration (EC50) of IP3 was about 1 microM. TSH, acetylcholine, and norepinephrine had no effect on the Ca2+ movement, but phosphatidylinositol 4,5-bisphosphate (PIP2) induced a similar Ca2+ release (EC50 = 3 microM). PIP2-induced release decreased as the Mg2+ concentration was raised. After the release induced by a maximal amount of IP3, PIP2 could induce a further Ca2+ release. We also measured Ca2+ efflux from fractionated microsomes preloaded with 45Ca2+ by ATP-dependent transport. IP3 induced a small efflux of 45Ca2+, but PIP2 was much more effective at low Mg2+ concentrations. More than half of the loaded 45Ca2+ was released by 10 microM PIP2 within 30 sec, and the EC50 was 0.7 microM. These results suggest that Ca2+ mobilization from the microsomes mediated by inositol compounds participates in the regulation of thyroid cell functions.
mesh_terms: D000109:Acetylcholine / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002451:Cell Compartmentation / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D066298:In Vitro Techniques; D015544:Inositol 1,4,5-Trisphosphate; D007295:Inositol Phosphates / Q000494:pharmacology*; D008861:Microsomes / Q000378:metabolism; D009638:Norepinephrine / Q000494:pharmacology; D019269:Phosphatidylinositol 4,5-Diphosphate; D010716:Phosphatidylinositols / Q000494:pharmacology*; D012503:Saponins / Q000494:pharmacology; D013403:Sugar Phosphates / Q000494:pharmacology*; D013552:Swine; D013961:Thyroid Gland / Q000378:metabolism*; D013972:Thyrotropin / Q000494:pharmacology
chemical_list: D007295:Inositol Phosphates; D019269:Phosphatidylinositol 4,5-Diphosphate; D010716:Phosphatidylinositols; D012503:Saponins; D013403:Sugar Phosphates; D015544:Inositol 1,4,5-Trisphosphate; D013972:Thyrotropin; D000109:Acetylcholine; D002118:Calcium; D009638:Norepinephrine