Activation of L-type calcium channels induces corticotropin-releasing factor secretion from human placental trophoblasts

The ultimate outcome of pregnancy, parturition, is a well orchestrated proc ess in which placental corticotropin-releasing factor (CRF) seems to play a n important role. The objective of the present study was to investigate the involvement of L-type calcium channels and calcium-dependent signaling in the depolarization-induced CRF release from human syncytiotrophoblast. The basal secretion of CRF by trophoblastic cells, isolated from human term pla centa, was maximal after their functional differentiation, which was monito red by hCG measurements. On the fourth day of culture, the basal CRF secret ion of the cells in serum-free medium was linear between 2 and 8 h. Incubat ion of the trophoblasts with KCl, a depolarizing stimulus, or with Bay K864 4, an L-type calcium channel agonist, for 3 or 8 h led to an increase in CR F secretion, but was without effect on its synthesis. This stimulated CRF r elease was calcium dependent, as it could be prevented by loading cells wit h 1,2-bis(0-Aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (acetoxymethyl) ester. Furthermore, the KCl-induced CRF secretion involved L-type calcium c hannels activation, as 2 mu mol/L nitrendipine, an L-type specific blocker, abolished the stimulation. In trophoblasts, where we have previously shown calcium-dependent protein kinase C (cPKCs) activity, incubation with Bay K 8644 also stimulated calcium calmodulin kinase II (CaMKII) and extracellula r regulated kinase activities. In the present study we observed that CaMKII and cPKCs were linked to the Bay K8644-induced secretion of CRF, as only t he autocamtide-2 related inhibitory peptide, a CaMKII inhibitor, and Go6976 , an inhibitor of mu and cPKCs partially prevented (30-78%) the activation of CRF release by Bay K8644. The use of PD 098056, an inhibitor of the ERKs kinases, showed no effect on CRF release. Taken together, these results su pport a depolarization-induced and calcium-dependent exocytotic-like secret ion of CRF from human placental trophoblasts. In addition, CaMKII and cPKCs seem to be potential modulators or mediators of these calcium effects on C RF secretion.