title: Inhibitors of ER Ca(2+)-ATPase activity deplete the ATP- and thrombin-sensitive Ca2+ pool in UMR 106-01 osteosarcoma cells.
abstract: While calcium release from intracellular stores is a signaling mechanism used universally by cells responding to hormones and growth factors, the compartmentalization and regulated release of calcium is cell type-specific. We employed thapsigargin and 2,5,-di-(tert-butyl)-1,4-benzohydroquinone (tBuHQ), two inhibitors of endoplasmic reticulum (ER) Ca(2+)-ATPase activity which block the transport of Ca2+ into intracellular stores, to characterize free Ca2+ compartmentalization in UMR 106-01 osteoblastic osteosarcoma cells. Each drug elicited transient increases in cytosolic free Ca2+ ([Ca2+]i), followed by a stable plateau phase which was elevated above the control [Ca2+]i. The release of Ca2+ from intracellular stores was coupled to an increased plasma membrane Ca2+ permeability which was not due to L-type Ca2+ channels. Thapsigargin and tBuHQ emptied the intracellular calcium pool which was released in response to either ATP or thrombin, identifying it as the inositol 1,4,5-trisphosphate-sensitive calcium store. The results of sequential and simultaneous additions of thapsigargin and tBuHQ indicate that both drugs depleted the same Ca2+ store and inhibited the same Ca(2+)-ATPase activity.
authors.affiliation: Department of Physiology and Cell Biology, University of Texas Medical School, Houston, USA.
authors.forename: J G
authors.initials: JG
authors.lastname: Meszaros
authors.forename: N J
authors.initials: NJ
authors.lastname: Karin
mesh_terms: D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D000975:Antioxidants / Q000494:pharmacology; D001859:Bone Neoplasms / Q000473:pathology; D002118:Calcium / Q000378:metabolism*; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors*; D002462:Cell Membrane / Q000378:metabolism; D002463:Cell Membrane Permeability / Q000187:drug effects; D003600:Cytosol / Q000187:drug effects / Q000378:metabolism; D004533:Egtazic Acid / Q000494:pharmacology; D004721:Endoplasmic Reticulum / Q000201:enzymology* / Q000378:metabolism; D016257:Fura-2 / Q000737:chemistry; D006873:Hydroquinones / Q000494:pharmacology; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism; D009543:Nifedipine / Q000494:pharmacology; D010006:Osteoblasts / Q000187:drug effects* / Q000378:metabolism; D012516:Osteosarcoma / Q000473:pathology; D013729:Terpenes / Q000494:pharmacology; D019284:Thapsigargin; D013917:Thrombin / Q000494:pharmacology; D014407:Tumor Cells, Cultured
chemical_list: D000975:Antioxidants; D006873:Hydroquinones; D013729:Terpenes; C019359:2,5-di-tert-butylhydroquinone; D004533:Egtazic Acid; D019284:Thapsigargin; D015544:Inositol 1,4,5-Trisphosphate; D000255:Adenosine Triphosphate; D013917:Thrombin; D000252:Calcium-Transporting ATPases; D009543:Nifedipine; D002118:Calcium; D016257:Fura-2