STIMULATION OF PLATELET-ACTIVATING-FACTOR (PAF) RECEPTORS INCREASES INOSITOL PHOSPHATE PRODUCTION AND CYTOSOLIC-FREE CA2-115 NEUROBLASTOMA-CELLS( CONCENTRATIONS IN N1E)

Platelet-activating factor 1-O-alkyl-2-acetyl-sn-glycero-3-phosphorylc holine, PAF) has recently been recognized as an important mediator in the pathophysiology of brain injury, This study demonstrates that, in suspended populations of N1E-115 cells loaded with Indo-1, biologicall y relevant concentrations of PAF produce a rapid and transient elevati on in cytosolic free calcium concentration ([Ca2+](i)). Moreover, nano molar concentrations of PAF increase [H-3]-inositol phosphate producti on. Using lyso-PAF and the specific PAF-receptor antagonists BN52021 a nd BN50739, we show that these effects were mediated by stimulation of PAF receptors. Experiments performed in Ca(2+)free medium show that P AF-induced [Ca2+](i) increase is the result of an influx of Ca2+ and o f the release of intracellular Ca2+ stores. Studies of Mn2+ influx arg ue in favour of additional pathways for PAF-induced Ca2+ influx other than the pathway for the thapsigargin-induced Ca2+ influx. Using the w hole-cell voltage-clamp technique, we observe that PAF induces an incr ease of Ltype Ca2+ current. However, the effects of La3+, nifedipine a nd KCI-induced depolarization on the PAF-induced [Ca2+](i) increase su ggest a minor participation of these voltage-gated Ca2+ channels in th e response to PAF, Altogether the results point to the existence of a PAF-induced Ca2+ influx through receptor-operated Ca2+ permeant channe ls.