Cellular permeation pathways in a leaky epithelium: the human amniochorion

Area of Science:

• Physiology
• Membrane Biology
• Perinatology

Background:

• Human fetal membranes, specifically the amniochorion, play crucial roles in regulating the intrauterine environment.
• Understanding their permeability is vital for fetal development and drug delivery research.

Purpose of the Study:

• To investigate the presence and characteristics of cellular permeation pathways in human fetal membranes at term.
• To quantify the electrical properties and diffusional coefficients for water and urea across these membranes.

Main Methods:

• Utilized Ussing-like chambers to measure electrical parameters: transepithelial potential (TEP), conductance (Gt), and intracellular potentials (cell PD).
• Determined water and urea diffusional coefficients (Pdw, Pdu) in intact membranes and isolated epithelial cell layers.
• Assessed the impact of ionic concentration changes (K+, Na+) and pharmacological agents (amiloride, ouabain) on cell potentials.

Main Results:

• The amniochorion exhibited a low TEP (0.1 mV) and high Gt (144 mS/cm2), indicating a leaky structure.
• Amnion cell potentials (cell PD) were -37 mV, influenced by K+, Na+ conductances, amiloride, and ouabain.
• The Pdw/Pdu ratio was higher in the amnion (4.0-7.0) than in the chorion (2.5-3.3), with the amnion cell layer being a more significant barrier.
• The amnion's diffusional properties resemble those of erythrocyte membranes and lecithin:cholesterol bilayers.

Conclusions:

• Human fetal membranes possess distinct transcellular permeation pathways.
• The amnion serves as a more effective barrier to water and urea diffusion compared to the chorion.
• Ionic transport across amnion cells is complex, involving K+, Na+, and specific drug-sensitive pathways.