CYTOSOLIC-FREE CA2-RELEASING-HORMONE( IN HUMAN SYNCYTIOTROPHOBLAST CELLS INCREASED BY GONADOTROPIN)

Effects of GnRH on free cytosolic Ca2+ concentrations ([Ca2+]i) were e xamined in individual first trimester human cytotrophoblast and syncyt iotrophoblast cells by fura-2 microspectrofluorimetry. GnRH (10(-6) m) did not affect [Ca2+]i in cytotrophoblasts on days 2-9 of culture, wi th 50 cells tested each day. GnRH (10(-6) m) did not affect [Ca2+]i on days 2-3, but increased [Ca2+]i in 15% of culture-derived syncytiotro phoblasts on day 4 (8 of 52 cells) and in 48% on days 5-9 of culture ( 158 of 332 cells). Culture-derived syncytiotrophoblasts originated fro m four first trimester placentae. GnRH increased [Ca2+]i in a prelimin ary trial using syncytiotrophoblasts derived directly from a single fi rst trimester placenta and cultured for 3 days (13 of 33 cells). Cultu re-derived first trimester syncytiotrophoblast cells that responded to 10(6) M GnRH (28 of 63 cells) on day 6 also responded to GnRH at 10(- 7) m (26 of 28 of the above cells), 10(-8) m (24 of 28 cells), 10(-9) m (22 of 28 cells), and 10(-10) m (3 of 28 cells). No cells responded to GnRH below a concentration of 10(-10) M. Desensitization of syncyti otrophoblasts by continuous GnRH perifusion (10(-6) m) and blockade of GnRH by competitive antagonism with Nal-Glu-GnRH (10(-6) m) suggested that effects of GnRH were receptor specific. The results provide dire ct evidence supporting the contention that the intracellular signaling resultant from GnRH receptor-ligand interactions in syncytiotrophobla sts may be at least partially mediated by transient increases in [Ca2]i.