title: Effect of hyposmotic challenge on microvillous membrane potential in isolated human placental villi.
abstract: This study examined the effect of hyposmotic solutions on the syncytiotrophoblast microvillous membrane potential (Em) in mature intermediate villi isolated from term human placentas. When villi were exposed to a control solution (280 mosmol/kgH2O; 116 mM NaCl) and then to either a 138-hyposmotic (138 mosmol/kgH2O; 37 mM NaCl) or 170-hyposmotic (170 mosmol/kgH2O; 55 mM NaCl) solution, there was a significant hyperpolarization of Em (-5.1 +/- 1.5 mV, P < 0.01 and -5.0 +/- 0.5 mV, P < 0.001, respectively; n = 10), which was reversible on removal of the hyposmotic stimulus. Low-NaCl (37 and 55 mM) solutions made isosmotic with control (i.e., 280 mosmol/kgH2O) by addition of raffinose did not significantly alter Em, suggesting that reducing NaCl concentration per se had no effect on Em. Exposure to 170-hyposmotic solution in the presence of 5 mM BaCl2 depolarized Em by +4.1 +/- 0.7 mV (P < 0.001, n = 6); BaCl2 similarly depolarized Em when added in control solution (+5.6 +/- 1. 1 mV, n = 5). Exposure to 170-hyposmotic solution containing 1 mM DIDS hyperpolarized Em by -9.0 +/- 1.7 mV (P < 0.001, n = 5). This degree of hyperpolarization was significantly greater than that observed in hyposmotic solution alone (P < 0.01) but was not different from the hyperpolarization when DIDS was added to control solution (-7.4 +/- 0.2 mV, n = 6). We conclude 1) that Ba2+-sensitive K+ conductances and DIDS-sensitive anion conductances contribute to the resting potential of the syncytiotrophoblast microvillous membrane and 2) that the syncytiotrophoblast microvillous membrane responds to a hyposmotic stimulus by activating both Ba2+-sensitive K+ and DIDS-sensitive anion conductances.
authors.affiliation: Department of Child Health and School of Biological Sciences, University of Manchester, St. Mary's Hospital, Manchester, M13 0JH, SW17 0RE United Kingdom. t.j.birdsey@sheffield.ac.uk
authors.forename: T J
authors.initials: TJ
authors.lastname: Birdsey
authors.forename: R D
authors.initials: RD
authors.lastname: Boyd
authors.forename: C P
authors.initials: CP
authors.lastname: Sibley
authors.forename: S L
authors.initials: SL
authors.lastname: Greenwood
mesh_terms: D002712:Chlorides / Q000378:metabolism; D004553:Electric Conductivity; D006801:Humans; D007038:Hypotonic Solutions / Q000494:pharmacology; D066298:In Vitro Techniques; D007552:Isotonic Solutions / Q000494:pharmacology; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D008871:Microvilli / Q000187:drug effects / Q000378:metabolism; D010920:Placenta / Q000378:metabolism*; D011188:Potassium / Q000378:metabolism; D014882:Water-Electrolyte Balance / Q000502:physiology*
chemical_list: D002712:Chlorides; D007038:Hypotonic Solutions; D007552:Isotonic Solutions; D011188:Potassium