title: Epidermal growth factor and sphingosine-1-phosphate stimulate Na+/H+ exchanger activity in the human placental syncytiotrophoblast.
abstract: The Na+/H+ exchanger (NHE) has a key role in intracellular pH ([pH]i) regulation of the syncytiotrophoblast in the human placenta and may have a role in the life cycle of this cell. In other cells the NHE (actually a family of up to 9 isoforms) is regulated by a variety of factors, but its regulation in the syncytiotrophoblast has not been studied. Here, we tested the hypotheses that EGF and sphingosine-1-phosphate (S1P), both of which affect trophoblast apoptosis and, in other cell types, NHE activity, stimulate syncytiotrophoblast NHE activity. Villous fragments from term human placentas were loaded with the pH-sensitive dye, BCECF. NHE activity was measured by following the recovery of syncytiotrophoblast [pH]i following an imposed acid load, in the presence and absence of EGF, S1P, and specific inhibitors of NHE activity. Both EGF and S1P caused a dose-dependent upregulation of NHE activity in the syncytiotrophoblast. These effects were blocked by amiloride 500 microM (a nonspecific NHE blocker) and HOE694 100 microM (NHE blocker with NHE1 and 2 isoform selectivity). Effects of EGF were also reduced by the NHE3 selective blocker S3226 (used at 1 microM). These data provide the first evidence that both EGF and S1P stimulate NHE activity in the syncytiotrophoblast; they appear to do so predominantly by activating the NHE1 isoform.
authors.affiliation: Maternal and Fetal Health Research Group, (Academic Unit of Child Health Univ. of Manchester, St. Mary's Hospital, Manchester M13 OJH.
authors.forename: E D
authors.initials: ED
authors.lastname: Johnstone
authors.forename: P F
authors.initials: PF
authors.lastname: Speake
authors.forename: C P
authors.initials: CP
authors.lastname: Sibley
mesh_terms: D002478:Cells, Cultured; D004305:Dose-Response Relationship, Drug; D004347:Drug Interactions; D004815:Epidermal Growth Factor / Q000008:administration & dosage*; D006801:Humans; D006863:Hydrogen-Ion Concentration; D008246:Lysophospholipids / Q000008:administration & dosage*; D010920:Placenta / Q000187:drug effects / Q000378:metabolism*; D017923:Sodium-Hydrogen Exchangers / Q000819:agonists* / Q000378:metabolism*; D013110:Sphingosine / Q000008:administration & dosage / Q000031:analogs & derivatives*; D014327:Trophoblasts / Q000187:drug effects / Q000378:metabolism*
chemical_list: D008246:Lysophospholipids; D017923:Sodium-Hydrogen Exchangers; C060506:sphingosine 1-phosphate; D004815:Epidermal Growth Factor; D013110:Sphingosine