Microvillous membrane potential ( E m) in villi from first trimester human placenta: comparison to E m at term.

The microvillous membrane (MVM) potential ( E m) of first trimester human placental villi was measured and compared with that in villi from term human placentas. The median E m in first trimester villi (-28 mV) was significantly more negative than that at term (-21 mV; P < 0.001). The median E m measured in villi from early ( weeks 6-11) first trimester (-32 mV) was significantly more negative than that in late ( weeks 12 and 13) first trimester villi (-24 mV; P < 0.001). Elevating extracellular KCl concentration induced a significant depolarization of E m in both first trimester and term villi ( P < 0.05 and P < 0.001, respectively). The magnitude of this depolarization was greater in first trimester than at term, indicating that the ion conductance of the MVM changes with gestation. Exposure to ouabain induced a significant depolarization of E m (3 mV: P < 0.05) in first trimester villi but had little effect at term. These results suggest that microvillous membrane electrophysiology changes with placental development. An alteration in the relative K+:Cl-conductance of the MVM is likely to be a major contributor to the change in the magnitude of E m.