Fluid transport across the epiblast of the early chick embryo

A simple method is described which allows quantitation of the rate of fluid transport across the isolated epiblast of the early chick embryo. This method consists of allowing the tissue to form spheres, which then spontaneously undergo a large volume increase. The rate of fluid uptake into the spheres can be estimated by measuring the dimensions of the spheres. Pharmacological and electrophysiological studies were performed on the spheres to determine the mechanisms of fluid transport. It was found that fluid is driven into the interior of the spheres by the osmotic gradient generated by unidirectional sodium transport and to a lesser extent by another mechanism, as yet unknown. We discuss possible candidates for this mechanism, and consider the significance of these findings to early development.

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Sodium transport and the control of epiblast polarity in the early chick embryo

Development ◽

10.1242/dev.77.1.73 ◽

1983 ◽

Vol 77 (1) ◽

pp. 73-98

Author(s):

Claudio D. Stern ◽

Debora O. MacKenzie

Keyword(s):

Chick Embryo ◽

Transport Properties ◽

Sodium Transport ◽

Primitive Streak ◽

Reverse Polarity ◽

Ouabain Binding ◽

Physiological Functions ◽

Rapid Reversal ◽

Electrophysiological Studies ◽

Morphological Polarity

The sodium transport properties of chick epiblast during gastrulation were studied by various techniques. It was found that the epiblast is capable of unidirectional apical tobasal sodium transport, in towards the underlying intraembryonic space. The Na-K-ATPasewas localized by [3H]ouabain binding and autoradiography near the basal surfaces of the cells, and the number of pump sites was quantified. The transport rate of sodium was determined with 22Na. Electrophysiological studies on embryos at primitive streak stages showed a transepithelial potential of about + 16 ± 5mV (basal side positive) which was sensitive to strophanthidin. Applying similar voltages but of reverse polarity to isolated sheets of epiblast caused a rapid reversal of some oftheir morphological polarity markers as well as some of their physiological functions. The relevance of these results to development is discussed.

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Ultrafiltration and Absorption in Evaluating Aquaporin Function from Peritoneal Transport of Sodium

Peritoneal Dialysis International ◽

10.1177/089686080702700616 ◽

2007 ◽

Vol 27 (6) ◽

pp. 687-690 ◽

Cited By ~ 7

Author(s):

Jacek Waniewski ◽

Malgorzata Debowska ◽

Bengt Lindholm

Keyword(s):

Water Transport ◽

Sodium Transport ◽

Fluid Transport ◽

Free Water ◽

Nephrol Dial Transplant ◽

Simple Method ◽

Water Fraction ◽

Sodium Diffusion ◽

The Impact ◽

Dialysate Sodium

Background Evaluation of free water transport is a tool for assessing aquaporin function in peritoneal dialysis patients. The dialysate “sodium dip” and estimation of sieving coefficient for sodium may be used for quantification of the free water fraction in ultrafiltration flow from blood to the peritoneal cavity. Method The mini peritoneal equilibration test (mini-PET) [La Milia et al., Nephrol Dial Transplant 2002; 17(Suppl 3):17–18] is a simple method for evaluating free water transport using sodium as a marker. We compared the evaluation of free water transport using the mini-PET against detailed data on fluid and sodium transport from clinical dwell studies using a macromolecular volume marker to estimate fluid absorption and ultrafiltration rates, and the modified Babb–Randerson–Farrell model to assess the sodium transport components. Results and Conclusion According to our results, the mini-PET may result in underestimation of fluid transport by about 20% because it neglects the impact of peritoneal fluid and solute absorption and sodium diffusion during the peritoneal dwell time. Nevertheless, estimation of the free water fraction in the mini-PET yields values (about 0.4) similar to the more detailed analysis.

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