K+ channel inhibition modulates the biochemical and morphological differentiation of human placental cytotrophoblast cells in vitro

Maintaining placental syncytiotrophoblast, a specialized multinucleated transport epithelium, is essential for normal human pregnancy. Syncytiotrophoblast continuously renews through differentiation and fusion of cytotrophoblast cells, under paracrine control by syncytiotrophoblast production of human chorionic gonadotropin (hCG). We hypothesized that K+ channels participate in trophoblast syncytialization and hCG secretion in vitro. Two models of normal-term placenta were used: 1 ) isolated cytotrophoblast cells and 2 ) villous tissue in explant culture. Cells and explants were treated with K+ channel modulators from 18 h, and day 3 , onward, respectively. Culture medium was analyzed for hCG, to assess secretion, as well as for lactate dehydrogenase (LDH), to indicate cell/tissue integrity. hCG was also measured in cytotrophoblast cell lysates, indicating cellular production. Syncytialization of cytotrophoblast cells was assessed by immunofluorescent staining of desmosomes and nuclei. Over 18–66 h, mononucleate cells fused to form multinucleated syncytia, accompanied by a 28-fold rise in hCG secretion. 1 mM Ba2+ stimulated cytotrophoblast cell hCG secretion at 66 h compared with control, whereas 5 mM tetraethylammonium (TEA) inhibited hCG secretion by >90%. 0.1–1 mM 4-aminopyridine (4-AP) reduced cytotrophoblast cell hCG secretion and elevated cellular hCG; without altering cellular integrity or syncytialization. In villous explants, hCG secretion was not altered by 1 mM Ba2+ but inhibited by 5 mM 4-AP and 5/10 mM TEA, without affecting LDH release. Anandamide, pinacidil, and cromakalim were without effect in either model. In conclusion, 4-AP- and TEA-sensitive K+ channels (e.g., voltage-gated and Ca2+-activated) regulate trophoblast hCG secretion in culture. If these K+ channels participate in hCG secretion in situ, they may regulate trophoblast turnover in health and disease.