Possible existence of two subsets of platelet-activating factor receptor to mediate polyphosphoinositide breakdown and calcium influx in neuroblastoma x glioma hybrid NG 108-15 cells.
Platelet-activating factor (PAF) initiated polyphosphoinositide (polyPI) breakdown and a rise of intracellular calcium concentration ([Ca2+]i) in neuroblastoma x glioma hybrid NG 108-15 cells. The accumulation of [3H]inositol trisphosphate and [3H]inositol bisphosphate was evident within 15 s after PAF stimulation, peaked at 1 min, and then gradually decayed. The increase in [3H]inositol monophosphate level was observed at 30 s, plateaued in 5 min, and was sustained up to 10 min in the presence of 10 mM LiCl. On the other hand, the rise of [Ca2+]i evoked by PAF reached a peak within 8-12 s and returned to basal levels within 1 min as measured in fura 2-loaded cells. When cells were suspended in Ca(2+)-depleted medium, the PAF-induced [Ca2+]i rise was reduced by 80%, indicating that the increase of [Ca2+]i was predominantly due to the Ca2+ influx from an extracellular source. Both PAF-induced accumulation of 3H-labeled inositol phosphates and [Ca2+]i elevation were concentration dependent with EC50 values of approximately 1 x 10(-10) and 5 x 10(-8) M, respectively. The PAF analogs 1-O-hexadecyl-2-hydroxy-sn-glycero-3-phosphocholine and 1-O-hexadecyl-2-O-methyl-rac-glycerol-3-phosphocholine were much poorer agonists at eliciting the same responses in these cells. Pretreatment of cells with pertussis toxin caused a substantial inhibition of PAF-induced accumulation of 3H-inositol phosphates. In contrast, the rise in [Ca2+]i was not significantly affected by toxin treatment at the same concentration.(ABSTRACT TRUNCATED AT 250 WORDS)
Chau
L Y
LY
Institute of Biomedical Sciences, Academia Sinica, Taipei, Taiwan, Republic of China.
Hu
C Y
CY
Chang
W T
WT
Hsu
Y S
YS
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism; D005910:Glioma / Q000378:metabolism* / Q000473:pathology; D006822:Hybrid Cells; D006868:Hydrolysis; D009447:Neuroblastoma / Q000378:metabolism* / Q000473:pathology; D009994:Osmolar Concentration; D037342:Pertussis Toxin; D010716:Phosphatidylinositols / Q000378:metabolism*; D010972:Platelet Activating Factor / Q000037:antagonists & inhibitors / Q000378:metabolism; D010980:Platelet Membrane Glycoproteins; D011956:Receptors, Cell Surface / Q000145:classification / Q000378:metabolism / Q000502:physiology*; D043562:Receptors, G-Protein-Coupled; D014407:Tumor Cells, Cultured; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
D010716:Phosphatidylinositols; D010972:Platelet Activating Factor; D010980:Platelet Membrane Glycoproteins; D011956:Receptors, Cell Surface; D043562:Receptors, G-Protein-Coupled; D010566:Virulence Factors, Bordetella; C039351:platelet activating factor receptor; D037342:Pertussis Toxin; D002118:Calcium