Effect of hyposmotic challenge on microvillous membrane potential in isolated human placental villi.
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.
Birdsey
T J
TJ
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
Boyd
R D
RD
Sibley
C P
CP
Greenwood
S L
SL
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*
D002712:Chlorides; D007038:Hypotonic Solutions; D007552:Isotonic Solutions; D011188:Potassium