title: P2-purinergic receptors in human breast tumor cells: coupling of intracellular calcium signaling to anion secretion.
abstract: ATP increases intracellular Ca++ ([Ca++]i) by activating different P2-purinoreceptors. Because ATP increases Cl- secretion in cystic fibrosis (CF)-affected epithelia, the current study was designed to establish the link between these two events. Studies were done in epithelial, human MCF-7 breast tumor cells in which the presence of mRNA transcripts encoding CF transmembrane conductance regulator was initially established. Changes in [Ca++]i were measured in single cells by fluorescence microscopy; anion transport was measured by 125I efflux. ATP stimulated concentration-dependent increases in [Ca++]i and 125I efflux from MCF-7 cells. The relative order of agonist potency of various selective P2-purinoreceptor agonists in increasing [Ca++]i and 125I efflux was: UTP > or = ATP > ADP = AMP; 2-chloro-ATP, 2-methylthio-ATP and AMP-phencyclidine were considerably less potent than ATP. The Ca++ ionophore ionomycin increased both intracellular [Ca++]i and 125I secretion. Exposing cells to the intracellular chelator ethylene glycol bis(beta-aminoethyl ether)-N,N'-tetra-acetic acid (EGTA)-acetoxymethylester decreased (AM) decreased ATP- and ionomycin-stimulated 125I efflux. Extracellular EGTA did not alter the Ca++ response to ATP, but inhibited the response to ionomycin. The chelator inhibited both ATP- and ionomycin-induced 125I secretion. Exposure of cells to nifedipine did not affect the responsiveness of MCF-7 cells to ATP. The anion transport antagonist 4,4'-diisothiocyananatostilbene-2,2'-disulfonic acid partially inhibited ATP- and cationophore-stimulated increases in [Ca++]i and 125I secretion. The data suggest that activation of P2 receptors in MCF-7 cells leads to an increase in anion transport as a result of the ability of ATP to increase [Ca++]i; moreover, anion channel antagonists may produce their inhibitory effect on 125I secretion, in part, by blocking agonist-induced intracellular Ca++ signaling.
authors.affiliation: Respiratory Health Network of Centres of Excellence, Montreal Chest Hospital Centre, Quebec, Canada.
authors.forename: M
authors.initials: M
authors.lastname: Flezar
authors.forename: S
authors.initials: S
authors.lastname: Heisler
mesh_terms: D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid; D012856:4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D000255:Adenosine Triphosphate / Q000494:pharmacology; D001943:Breast Neoplasms / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism*; D018118:Chloride Channels; D002712:Chlorides / Q000378:metabolism*; D003550:Cystic Fibrosis / Q000378:metabolism; D019005:Cystic Fibrosis Transmembrane Conductance Regulator; D004305:Dose-Response Relationship, Drug; D006801:Humans; D007457:Iodine Radioisotopes / Q000378:metabolism; D007473:Ion Channels / Q000187:drug effects; D008565:Membrane Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D011983:Receptors, Purinergic / Q000378:metabolism*; D015398:Signal Transduction; D014407:Tumor Cells, Cultured
chemical_list: C505032:CFTR protein, human; D018118:Chloride Channels; D002712:Chlorides; D007457:Iodine Radioisotopes; D007473:Ion Channels; D008565:Membrane Proteins; D012333:RNA, Messenger; D011983:Receptors, Purinergic; D019005:Cystic Fibrosis Transmembrane Conductance Regulator; D012856:4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid; D000255:Adenosine Triphosphate; D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid; D002118:Calcium