title: Hydrogen peroxide attenuates store-operated calcium entry and enhances calcium extrusion in thyroid FRTL-5 cells.
abstract: Redox modulation participates in the regulation of intracellular free calcium concentration ([Ca(2+)](i)) in several cell types. In thyroid cells, including FRTL-5 cells, changes in [Ca(2+)](i) regulate several important functions, including the production of H(2)O(2) (hydrogen peroxide). As H(2)O(2) is of crucial importance for the production of thyroid hormones, we investigated the effects of H(2)O(2) on [Ca(2+)](i) in thyroid FRTL-5 cells. H(2)O(2) itself did not modulate basal [Ca(2+)](i). However, H(2)O(2) attenuated store-operated calcium entry evoked by thapsigargin, both in a sodium-containing buffer and in a sodium-free buffer. The effect of H(2)O(2) was abrogated by the reducing agent beta-mercaptoethanol. H(2)O(2) also attenuated the thapsigargin-evoked entry of barium and manganese. The effect of H(2)O(2) was, at least in part, mediated by activation of protein kinase C (PKC), as H(2)O(2) enhanced the binding of [(3)H]phorbol 12,13-dibutyrate. H(2)O(2) also stimulated the translocation of the isoenzyme PKCepsilon from the cytosolic fraction to the particulate fraction. Furthermore, H(2)O(2) did not attenuate store-operated calcium entry in cells treated with staurosporine or calphostin C, or in cells with down-regulated PKC. H(2)O(2) depolarized the membrane potential in bisoxonol-loaded cells and when patch-clamp in the whole-cell mode was used. The depolarization was attenuated in cells with down-regulated PKC. This depolarization, at least in part, explained the H(2)O(2)-evoked inhibition of calcium entry. In addition, H(2)O(2) enhanced the extrusion of calcium from cells stimulated with thapsigargin and this effect was abolished in cells with down-regulated PKC and after treatment of the cells with the reducing agent beta-mercaptoethanol. In conclusion H(2)O(2) attenuates an increase in [Ca(2+)](i). As H(2)O(2) is produced in thyroid cells in a calcium-dependent manner, our results suggest that H(2)O(2) may participate in the regulation of [Ca(2+)](i) in these cells via a negative-feedback mechanism involving activation of PKC.
authors.affiliation: Department of Biology, Abo Akademi University, BioCity, Artillerigatan 6, 20520 Turku, Finland and Minerva Foundation Institute for Medical Research, 00250 Helsinki, Finland. kid.tornqvist@abo.fi
authors.forename: K
authors.initials: K
authors.lastname: Törnquist
authors.forename: P J
authors.initials: PJ
authors.lastname: Vainio
authors.forename: S
authors.initials: S
authors.lastname: Björklund
authors.forename: A
authors.initials: A
authors.lastname: Titievsky
authors.forename: B
authors.initials: B
authors.lastname: Dugué
authors.forename: R K
authors.initials: RK
authors.lastname: Tuominen
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D001464:Barium / Q000378:metabolism; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000378:metabolism; D000252:Calcium-Transporting ATPases / Q000378:metabolism; D002460:Cell Line; D015536:Down-Regulation / Q000187:drug effects; D004789:Enzyme Activation / Q000187:drug effects; D006861:Hydrogen Peroxide / Q000494:pharmacology*; D007527:Isoenzymes / Q000378:metabolism; D008345:Manganese / Q000378:metabolism; D008564:Membrane Potentials / Q000187:drug effects; D008623:Mercaptoethanol / Q000494:pharmacology; D009281:Naphthalenes / Q000494:pharmacology; D010084:Oxidation-Reduction / Q000187:drug effects; D015240:Phorbol 12,13-Dibutyrate / Q000378:metabolism; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000378:metabolism; D021381:Protein Transport / Q000187:drug effects; D051381:Rats; D012964:Sodium / Q000494:pharmacology; D019311:Staurosporine / Q000494:pharmacology; D019284:Thapsigargin / Q000494:pharmacology; D013961:Thyroid Gland / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism*
chemical_list: D015220:Calcium Channels; D007527:Isoenzymes; D009281:Naphthalenes; D001464:Barium; D015240:Phorbol 12,13-Dibutyrate; D008345:Manganese; D008623:Mercaptoethanol; D019284:Thapsigargin; D000255:Adenosine Triphosphate; D012964:Sodium; D006861:Hydrogen Peroxide; D011493:Protein Kinase C; D000252:Calcium-Transporting ATPases; D019311:Staurosporine; C058819:calphostin C; D002118:Calcium