Platelet-activating factor increases intracellular calcium levels in preimplantation stage embryos

Platelet-activating factor [1-O-alkyl-2-acetyl-sn-glycero-3-phosphocholine;PAF] has an active role in preimplantation embryo development. PAF has been shown to act via the receptor mediated inositol triphosphate-diacylglycerol (IP3/DAG) pathways in non-reproductive cells to increase intracellular calcium ([Ca++]i) levels. Molecular evidence on the presence of the PAF-receptor in mouse preimplantation embryos has recently been reported, however the effect of PAF on embryonic [Ca++]i is unclear. Therefore, the study objective was to determine the effect of PAF on [Ca++]i in the mouse preimplantation embryo. Two-cell embryos were collected from PMSG/hCG primed mature female CFW mice, washed in modified M16 (phenol red free) and loaded with FURA-2AM (0.2 microM). Background [Ca++]i levels were measured for a minimum of 120 seconds prior to treatment. PAF or lyso-PAF (the biological inactive form) were added [10-7 M final concentration] and [Ca++]i levels measured. Background, nonstimulated, [Ca++]i levels had a mean of 131.4 nM. [Ca++]i levels began to increase by 4.6 seconds with maximum levels reached by 179.9 seconds after PAF exposure, baseline levels returned by 460 seconds. Maximum [Ca++]i levels (405.9 nM mean) were 3X that of non-PAF or lyso-PAF exposure. The results further demonstrate the magnitude of PAFs' action in the preimplantation embryo period. PAF's mechanism of action, in preimplantation mouse embryos, appears to involve a PAF-receptor mediated increase in intracellular calcium.