van Dijk J P, van Kreel B K
J Dev Physiol. 1982 Feb;4(1):23-38.
Knowledge of the magnitude of the electric potential differences between the maternal and fetal circulations and the trophoblast is necessary to describe transport of ions into and out of the trophoblast as it occurs in placental transfer of charged molecules. The value of the electric potential difference is also of significance in describing the transport of neutral molecules when their transport is coupled to electrogenic co-transport systems. We developed a method to obtain the values of these potential differences, in the isolated guinea-pig placenta perfused on both sides with an artificial medium. A positively charged ion that carries a radioactive label is allowed to equilibrate between the trophoblast and its circulations. The intracellular equilibrium concentration can be calculated and, because the extracellular concentration is known, the potential difference can be obtained with the Nernst equation. Rapid equilibrium is obtained by charging the trophoblast by means of perfusion of the placenta with the ion at a high concentration, followed by reduction of the concentration in the medium until equilibrium is observed. This is done in both a continuous and discontinuous manner. In addition to measurements of the potential differences, their origin was investigated. It was shown that at least part of the potential difference is generated by the action of transcellular Na--K exchange, because depolarization could always be obtained by decreasing the transmembrane Na and K gradients. Mean values obtained were delta psi F = 71 +/- 21 mV (+/- SD) for the potential difference between the fetal circulation and the trophoblast and delta psi m = 64 +/- 16 mV for the potential difference between the maternal side and the trophoblast with the cell interior negative.
了解母胎循环与滋养层之间的电势差大小对于描述离子进出滋养层的转运是必要的，因为这发生在带电分子的胎盘转运过程中。当电中性分子的转运与生电共转运系统偶联时，电势差的值对于描述其转运也具有重要意义。我们开发了一种方法来获取这些电势差的值，该方法是在两侧用人工培养基灌注的离体豚鼠胎盘中进行的。携带放射性标记的带正电离子在滋养层与其循环之间达到平衡。可以计算细胞内平衡浓度，并且由于细胞外浓度是已知的，因此可以通过能斯特方程获得电势差。通过用高浓度的离子灌注胎盘使滋养层带电，然后降低培养基中的浓度直至观察到平衡，从而实现快速平衡。这可以通过连续和不连续的方式完成。除了测量电势差之外，还研究了它们的来源。结果表明，至少部分电势差是由跨细胞钠钾交换的作用产生的，因为通过降低跨膜钠和钾梯度总能获得去极化。所获得的平均值为：胎儿循环与滋养层之间的电势差ΔψF = 71±21 mV（±标准差），母体侧与滋养层之间的电势差Δψm = 64±16 mV，细胞内为负。
