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This work is about a characterisation, in the electrophysiological sense, of the amnion.
It protects the embryo from dehydratation, changes in temperature, and mechanical influences. But it also serves as a barrier between the embryonic membranes and the blood vessels. For these functions the accumulated amniotic liquid is very important.
The volume of amniotic liquid rises rapidly from incubation-day (D) 6 to7 and then continuously accumulates until D13 up to 3 - 4 ml. The mechanisms witch lead to this amount of liquid were not scientifically established up to now. Romanoff (1960) offers these two theories: As a product of secretion of the amniotic epithelium, wich developed from the internal ectoderm. Or as transsudate from blood vessels into the area pellucida.
On D9 - 17 the amnion shows its strongest growth.
Its musculature starts, depending on different authors, on D 5 or 6 with its rhythmic contractions. These reach their maximum on D 8/9/12 (different authors ).
Epple et. al. (1992) describe the amounts of catecholamines in the different extraembryonic cavities after various stresses of a different kind. They show, that the amnion has a function as a barrier.
To explore these transport processes an electrophysiological characterisation of the amniotic membrane is necessary:
• The transmembranous voltage produced by the amnion allows a determination of electrochemical gradients.
• Determination of transmembranous Na+ - transport can explain a secondarily active water transport
• Determination of transmembranous Ca+ - transport to help locate the source of Calcium needed for the rhythmic amnion contractions or to show a participation of the amnion in the delivery of Ca+ from the eggshell.
It was decided to measure these parameters on D9 and 10, because in these days the greatest activity can be expected on the membrane.
Later days are also to be excluded, because from D10 on the sero-amniotic connection is slowly degraded. The following influx of albumen would change the osmotic conditions in the amniotic liquid and so falsify the determination of purely active transport mechanisms.
Material and Methods:
After the amnion is isolated and cleaned, it is entirely transferred into the Ussing chamber.
In the first part of the measurements only the transmembranous voltage is measured.
This voltage over the amnion is then equalized by short current impulses to exclude transport processes caused by electrochemical gradient.
The second part aims to achieve a net transport of sodium and calcium.
Isotopes of each are added one side and their appearance on the other is measured in definite time intervals. This is done in both directions, then the net can be calculated
With the results it can be conluded to the presence of already well studied transport-channels and carrier systems.
In future studies these shall then be influenced by various conditions and stressors (von Blumröder and Tönhardt, 2002). Impulses for medicine in humans can also be expected.
A lack of amniotic fluid can e.g. cause neonatale dysplasia coxae luxans and other diseases in young born humans.
Calcium-transport, maybe a simulation of heart- and circulation- diseases is possible.
Here the smooth muscle cells in the amnion could serve as model for the muscles in blood vessels.