Effect of platelet-activating factor (PAF) on cytosolic free calcium in human peripheral blood mononuclear leukocytes.

Cytosolic free calcium concentration, [Ca2+]i, in human peripheral blood mononuclear leukocytes was increased by platelet-activating factor (PAF) dose-dependently. The response was transient and was attenuated by EGTA (2 mM) in the medium. Furthermore, pretreatment of the cells with pertussis toxin did not alter significantly the rise in [Ca2+]i after stimulation by PAF. The data suggest that elevation of [Ca2+]i in human mononuclear leukocytes induced by PAF depends on: (1) calcium influx through calcium channels in the plasma membranes and (2) calcium mobilization from internal stores mediated via pathway(s) that is insensitive to the action of pertussis toxin.