title: Endothelin-1-evoked calcium transients in UMR-106 osteoblastic osteosarcoma cells are mediated through endothelin-A and endothelin-B receptors.
abstract: Endothelin (ET) receptor subtypes involved in the modulation of intracellular calcium were studied in UMR-106 osteoblastic osteosarcoma cells. Calcium signaling in UMR-106 cells in suspension was determined with fluo-3-acetoxymethylester fluorescent dye. ET-1 and the ETB-selective agonist sarafotoxin 6c (S6c) elicited rapid calcium transients. Maximally effective concentrations of the ETA-selective antagonist BQ-123 [Cyclo(-D-Trp-D-Asp-Pro-D-Val-Leu)] attenuated ET-1-evoked calcium transients by only 50%. BQ-123 had no effect on S6c-stimulated transients. ET-1 and S6c showed homologous desensitization on repeated administration. Pretreatment with ET-1 completely eliminated S6c-evoked calcium transients, whereas S6c pretreatment only partially (50%) attenuated the calcium transient evoked by ET-1. Joint pretreatment with S6c and BQ-123 or pretreatment with the ETA/ETB nonselective antagonist PD-142893 (Ac-D-diphenylalanine-Leu-Asp-Ile-Ile-Trp) eliminated the ET-1-stimulated calcium transient. These cells display both ETA and ETB receptors (60:40), as demonstrated by saturation binding experiments with [125I] ET-1 and the ETB specific agonist, [125I] IRL-1620 (Suc [Glu9, Ala11,15] endothelin-1 [8-21]). This was further confirmed by competition binding experiments using [125I] ET-1 and subtype-selective ligands S6c and BQ-123. These data indicate that ET-1 interacts with both ETA and ETB receptors to elicit calcium transients in UMR-106 osteoblastic osteosarcoma cells.
authors.affiliation: Department of Pharmacology, Northwestern University Medical School, Chicago, Illinois.
authors.forename: D E
authors.initials: DE
authors.lastname: Semler
authors.forename: E H
authors.initials: EH
authors.lastname: Ohlstein
authors.forename: P
authors.initials: P
authors.lastname: Nambi
authors.forename: C
authors.initials: C
authors.lastname: Slater
authors.forename: P H
authors.initials: PH
authors.lastname: Stern
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001667:Binding, Competitive; D002118:Calcium / Q000502:physiology*; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D065128:Endothelin Receptor Antagonists; D016232:Endothelins / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D066298:In Vitro Techniques; D008969:Molecular Sequence Data; D009842:Oligopeptides / Q000494:pharmacology; D012516:Osteosarcoma / Q000378:metabolism*; D010456:Peptides, Cyclic / Q000494:pharmacology; D051381:Rats; D044022:Receptor, Endothelin A; D044023:Receptor, Endothelin B; D017466:Receptors, Endothelin / Q000502:physiology*; D014757:Viper Venoms / Q000494:pharmacology
chemical_list: D065128:Endothelin Receptor Antagonists; D016232:Endothelins; D009842:Oligopeptides; D010456:Peptides, Cyclic; D044022:Receptor, Endothelin A; D044023:Receptor, Endothelin B; D017466:Receptors, Endothelin; D014757:Viper Venoms; C057354:sarafotoxins s6; C076213:PD 142893; C072247:cyclo(Trp-Asp-Pro-Val-Leu); D002118:Calcium