Platelet-activating factor stimulates a rapid accumulation of inositol (1,4,5)trisphosphate in guinea pig eosinophils: relationship to calcium mobilization and degranulation.
The effect of platelet-activating factor (PAF) on inositol (1,4,5)trisphosphate (Ins[1,4,5]P3) mass, calcium mobilization, and the release of granule enzymes was studied on guinea pig peritoneal eosinophils (EOSs). PAF evoked a concentration-dependent accumulation of Ins(1,4,5)P3 with a drug concentration that elicits 50% of the maximum attainable response (EC50) of 10 nmol/L; the production of this second messenger was maximal at 1 mumol/L of PAF. Kinetic analysis of PAF (1 mumol/L)-induced Ins(1,4,5)P3 accumulation demonstrated it to be transient with a 3.8-fold increase over resting levels observed at 5 seconds. Thereafter, the level of Ins(1,4,5)P3 declined, returning to vehicle-treated levels 60 seconds after PAF challenge. Lyso-PAF, the inactive precursor and metabolite of PAF, was inactive at all concentrations examined. PAF also induced a rapid, concentration-dependent (EC50, 12 nmol/L) rise in the cytosolic-free calcium concentration ([Ca++]i) in fura 2-AM-loaded EOSs that was transient, peaking after the maximum increase in Ins(1,4,5)P3 mass was observed. A highly significant positive correlation was found between the peak increase in Ins(1,4,5)P3 and the peak rise in [Ca++]i. Functionally, PAF evoked a concentration-dependent release of granule constituents from both the small (arylsulfatase B; EC50, 3 nmol/L) and specific (EOS peroxidase; EC50, 2.7 nmol/L) granules that lagged, temporally, behind both Ins(1,4,5)P3 accumulation and the rise in [Ca++]i. Both the biochemical and functional effects of PAF examined in this study were antagonized by WEB 2086 (300 nmol/L), a selective PAF receptor-blocking drug. It is concluded that stimulus (PAF)-response coupling in guinea pig peritoneal EOSs may involve the receptor-mediated formation of Ins(1,4,5)P3 and subsequent release of intracellularly stored Ca++. This sequence of events may link PAF receptor activation to Ca(++)-dependent cellular responses, such as degranulation.
Kroegel
C
C
Department of Thoracic Medicine, National Heart & Lung Institute, Royal Brompton and National Heart and Lung Hospital, London, England.
Chilvers
E R
ER
Giembycz
M A
MA
Challiss
R A
RA
Barnes
P J
PJ
D000818:Animals; D001381:Azepines / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002469:Cell Separation; D003594:Cytoplasmic Granules / Q000187:drug effects / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004804:Eosinophils / Q000737:chemistry / Q000187:drug effects* / Q000378:metabolism; D006168:Guinea Pigs; D015544:Inositol 1,4,5-Trisphosphate / Q000032:analysis / Q000378:metabolism*; D008297:Male; D010529:Peritoneal Cavity / Q000166:cytology; D010972:Platelet Activating Factor / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D015290:Second Messenger Systems / Q000187:drug effects / Q000502:physiology; D013268:Stimulation, Chemical; D013997:Time Factors; D014230:Triazoles / Q000494:pharmacology
D001381:Azepines; D010972:Platelet Activating Factor; D014230:Triazoles; C052518:WEB 2086; D015544:Inositol 1,4,5-Trisphosphate; D002118:Calcium