Arachidonic acid stimulates 45calcium efflux and hPL release in isolated trophoblast cells

Previous investigations from this laboratory have indicated that arachidonic acid stimulates a rapid, dose-dependent and reversible increase in hPL release which is not dependent on cyclooxygenase or lipoxygenase metabolism. To investigate further the mechanism by which arachidonic acid stimulates the release of hPL, the effect of arachidonic acid on the release of 45Ca from perifused cells prelabelled with 45CaCl was examined in an enriched cell culture population of term human syncytiotrophoblast. Arachidonic acid (10-100 microM) stimulated a dose-dependent, rapid, and reversible increase in the release of both 45Ca and hPL from the perifused placental cells. On the other hand, palmitic acid had little effect on either hPL release or 45Ca release even at concentrations as high as 100 microM. Ionophore A23187 (1-10 microM) also stimulated a dose-dependent and reversible increase in hPL release. Since arachidonic acid increases the mobilization of cellular calcium, as reflected by the increased 45calcium efflux, and since an increase in the intracellular calcium concentration appears to stimulate an increase in hPL release, these results suggest that the stimulation of hPL release by arachidonic acid may be due, at lease in part, to the effects of the fatty acid on cellular calcium mobilization.