Two distinct pathways of platelet-activating factor-induced hydrolysis of phosphoinositides in primary cultures of rat Kupffer cells.
Stimulation of rat Kupffer cells in primary culture with platelet-activating factor (PAF) caused a rapid hydrolysis of phosphatidylinositol 4,5-bisphosphate and phosphatidylinositol 4-phosphate with a concomitant increase in the levels of myo-inositol 1,4,5-trisphosphate and myo-inositol 1,4-bisphosphate. This phospholipase C-mediated hydrolysis of polyphosphoinositides was independent of extracellular Ca2+ but was inhibited by the intracellular Ca2+ antagonist TMB-8. A second slower response to PAF was characterized by deacylation of PI leading to the accumulation of glycerophosphoinositol (GPI). PAF-induced GPI synthesis was not inhibited by TMB-8. These effects of PAF were accompanied by initial transient mobilization of Ca2+ from intracellular stores followed by a rather slow influx of Ca2+ from the extracellular medium. PAF-stimulated deacylation and phosphodiesteric hydrolysis of inositol lipids were differentially affected by cholera toxin and pertussis toxin. Pretreatment of the Kupffer cells with either of these toxins caused inhibition of phospholipase C activity. Pertussis toxin also inhibited PAF-stimulated deacylation. However, cholera toxin itself stimulated GPI release and addition of PAF to the cholera toxin-treated cells caused a further increase in GPI release. Phorbol ester inhibited PAF-induced phosphodiesteric hydrolysis of phosphoinositides, but not deacylation. PAF-induced metabolism of phosphoinositides was inhibited by the PAF antagonist, U66985. These results suggest that PAF-induced phosphodiesteric hydrolysis and deacylation of inositol phospholipids are regulated via distinct mechanisms involving activation of separate G-proteins in rat Kupffer cells. Also the regulation of phosphoinositide metabolism by Ca2+ mobilization from two separate Ca2+ pools is indicated by this study.
Gandhi
C R
CR
Department of Biochemistry, University of Texas Health Science Center, San Antonio 78284.
Hanahan
D J
DJ
Olson
M S
MS
D000818:Animals; D002118:Calcium / Q000378:metabolism; D002478:Cells, Cultured; D002772:Cholera Toxin / Q000494:pharmacology; D002851:Chromatography, High Pressure Liquid; D004533:Egtazic Acid / Q000494:pharmacology; D005707:Gallic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D066298:In Vitro Techniques; D007295:Inositol Phosphates / Q000378:metabolism; D007728:Kupffer Cells / Q000378:metabolism*; D037342:Pertussis Toxin; D010716:Phosphatidylinositols / Q000378:metabolism*; D010972:Platelet Activating Factor / Q000031:analogs & derivatives / Q000494:pharmacology*; D010980:Platelet Membrane Glycoproteins; D051381:Rats; D011956:Receptors, Cell Surface / Q000187:drug effects; D043562:Receptors, G-Protein-Coupled; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D013997:Time Factors; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
D007295:Inositol Phosphates; 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; D004533:Egtazic Acid; C006014:8-(N,N-diethylamino)octyl-3,4,5-trimethoxybenzoate; D005707:Gallic Acid; D002772:Cholera Toxin; C046779:U 66985; D037342:Pertussis Toxin; D013755:Tetradecanoylphorbol Acetate; D002118:Calcium