title: Platelet-activating factor receptor-mediated calcium influx in NG 108-15 cells.
abstract: Platelet-activating factor (PAF) elicited an increase in intracellular Ca2+ concentration, [Ca2+]i, in neuroblastoma x glioma hybrid NG 108-15 cells as measured by fura-2 fluorescence method. The rise in [Ca2+]i was primarily due to the influx of Ca2+ from extracellular source. Preincubation of cells with the Ca(2+)-ion channel blockers, including verapamil, nifedipine and conotoxin, did not affect the Ca(2+)-response stimulated by PAF, indicating that the PAF-elicited Ca(2+)-influx is not mediated through the classical voltage-dependent Ca(2+)-ion channels. In contrast, SK&F 96365, which is an inhibitor of receptor-operated calcium channel, blocked the PAF-elicited Ca(2+)-response dose-dependently. When cells were pretreated with the protein kinase C activator, phorbol 12-myristate 13-acetate (PMA), PAF-elicited Ca(2+)-signal was diminished substantially. In contrast, the protein kinase A activator, forskolin, has no effect on the Ca(2+)-response induced by PAF. Further experiment demonstrated that genistein, an inhibitor of tyrosine kinase, also caused inhibition on PAF-induced Ca(2+)-response significantly. There results suggest that the PAF receptor-coupled Ca(2+)-ion channel is subjected to the modulation by protein kinase C and tyrosine-specific kinase. Pretreatment of cells with PAF resulted in the desensitization of the Ca(2+)-response following further stimulation with the same agonist. The heterologous desensitization of the PAF-induced Ca2+ influx was also observed in cells pretreated with bradykinin or to a less extent with ATP. Conversely, pretreatment of cells with PAF affected only partially the Ca(2+)-response elicited by bradykinin or ATP. Additive response was observed when PAF and ATP were added together but not PAF and bradykinin.
authors.affiliation: Division of Cardiovascular Research, Institute of Biomedical Sciences, Academia Sinica, Taipei, Taiwan, Republic of China.
authors.forename: L Y
authors.initials: LY
authors.lastname: Chau
authors.forename: C Y
authors.initials: CY
authors.lastname: Hu
mesh_terms: D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D001920:Bradykinin / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D005910:Glioma / Q000378:metabolism; D006822:Hybrid Cells / Q000378:metabolism; D051379:Mice; D009447:Neuroblastoma / Q000378:metabolism; D010972:Platelet Activating Factor / Q000494:pharmacology; D010980:Platelet Membrane Glycoproteins / Q000502:physiology*; D011494:Protein Kinases / Q000502:physiology; D051381:Rats; D011956:Receptors, Cell Surface; D043562:Receptors, G-Protein-Coupled; D014407:Tumor Cells, Cultured
chemical_list: D010972:Platelet Activating Factor; D010980:Platelet Membrane Glycoproteins; D011956:Receptors, Cell Surface; D043562:Receptors, G-Protein-Coupled; C039351:platelet activating factor receptor; D000255:Adenosine Triphosphate; D011494:Protein Kinases; D001920:Bradykinin; D002118:Calcium