Membrane potential and input resistance in syncytiotrophoblast of human term placenta in vitro

Direct measurements of electrical potential and input resistance were performed on the syncytial membrane facing maternal blood. The potentials varied according to the external potassium ion levels and, to a lesser extent, with sodium ion concentrations. Ouabain provoked a rapid and consistent depolarization which indicates an electrogenic component. Amiloride slightly hyperpolarized the membrane, confirming the predominant role of potassium ions in the control of the diffusional component of the membrane potential. The electrical potential revealed in this study might play a part in the maternofetal transport of ions.