Stimulation of calcium influx by platelet activating factor in Dictyostelium.
Platelet activating factor (PAF) induces Ca2+ influx in Dictyostelium discoideum. In this investigation we used this activity to analyze the mechanism of PAF action. We found that PAF activity was confined to the period of spike-shaped oscillations and suggest that the role of PAF is to augment cAMP relay. PAF seems to act only a few times during this time period of two hours, since Ca2+ entry adapted to a subsequent stimulus for about 30 minutes. PAF showed a reduced response in the G protein beta- strain LW14 and was unable to induce Ca2+ influx in the G alpha 2- strains HC85 and JM1. The latter expresses the cAMP receptors cAR1 constitutively, and exhibits cAMP-induced Ca2+ influx, albeit at a reduced level. In order to decide whether the inability of PAF to elicit a Ca2+ response in JM1 cells was due to the lack of differentiation and/or the lack of G alpha 2, we inhibited the IP3-dependent pathway with compound U73122 and found that Ca2+ entry was blocked, whereas a closely related inactive compound, U73343, did not alter the response. In agreement with this, NBD-Cl, an inhibitor of Ca2+ uptake into the IP3-sensitive store in Dictyostelium, also abolished PAF activity. The latter was not inhibited by the plasma membrane antagonists BN-52021 or WEB 2170. Therefore PAF seems to operate intracellularly via the IP3-signalling pathway at or upstream of the IP3-sensitive store.
Schaloske
R
R
Faculty of Biology, University of Konstanz, FRG.
Sordano
C
C
Bozzaro
S
S
Malchow
D
D
D009327:4-Chloro-7-nitrobenzofurazan / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D000242:Cyclic AMP / Q000494:pharmacology*; D004023:Dictyostelium / Q000187:drug effects / Q000502:physiology*; D004224:Diterpenes; D004305:Dose-Response Relationship, Drug; D004963:Estrenes / Q000494:pharmacology; D019204:GTP-Binding Proteins / Q000502:physiology; D046934:Ginkgolides; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism; D007700:Kinetics; D007783:Lactones / Q000494:pharmacology; D010972:Platelet Activating Factor / Q000031:analogs & derivatives / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D011760:Pyrrolidinones / Q000494:pharmacology; D013045:Species Specificity; D013997:Time Factors
D004224:Diterpenes; D004963:Estrenes; D046934:Ginkgolides; D007783:Lactones; C029271:O-deacetyl platelet activating factor; D010972:Platelet Activating Factor; D011760:Pyrrolidinones; C074854:U 73343; D015544:Inositol 1,4,5-Trisphosphate; C045856:ginkgolide B; D000242:Cyclic AMP; D019204:GTP-Binding Proteins; D009327:4-Chloro-7-nitrobenzofurazan; D002118:Calcium