AREGU May 45/5

Birdsey, T. J., R. D. H. Boyd, C. P. Sibley, and S. L. Greenwood. Effect of hyposmotic challenge on microvillous membrane potential in isolated human placental villi. Am. J. Physiol. 276 (Regulatory Integrative Comp. Physiol. 45): R1479–R1488, 1999.—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 (25.1 6 1.5 mV, P , 0.01 and 25.0 6 0.5 mV, P , 0.001, respectively; n 5 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 14.1 6 0.7 mV (P , 0.001, n 5 6); BaCl2 similarly depolarized Em when added in control solution (15.6 6 1.1 mV, n 5 5). Exposure to 170-hyposmotic solution containing 1 mM DIDS hyperpolarized Em by 29.0 6 1.7 mV (P , 0.001, n 5 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 (27.4 6 0.2 mV, n 5 6). We conclude 1) that Ba21-sensitive K1 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 Ba21-sensitive K1 and DIDS-sensitive anion conductances.