The effect of Ca++, Mg++ and H+ on the capillary permeability of the rete mirabile of the eel, Anguilla vulgaris L.

The effects of EDTA, and of varying pH on the capillary permeability in the rete mirabile have been investigated: EDTA had to be added to the perfusate in excess to the total content of Ca++ and Mg++ in plasma in order to elicit changes in the permeability. When exposed to sufficient amounts of EDTA, the capillary permeability to hydrophilic molecules increased several fold whereas the permeability to THO and lipid-soluble molecules remained unchanged. The increase in the permeability to high-molecular dextrans was delayed. When the EDTA-effect was maximal the mutual relationship between the permeabilities of THO and the lipid-insoluble molecules became close to the ratio between the corresponding free diffusion coefficients in water. During exposure to EDTA the content of K+ and Na+ of the rete tissue (mostly endothelial cells) became very similar to that of plasma. Similar effects were obtained when the rete was perfused with plasma having a pH below 4 or above 9. The EDTA-effect was reversible during its initial stage. Perfusions with plasma in which Ca and Mg had been removed by dialysis at pH 3.5 were performed. When an EDTA-effect had been induced with this type of perfusates, it could be reversed by addition of equimolar amounts of either Ca++ or Mg++. This indicates Ca++ and Mg++ to be equally important in order to assure normal permeability properties of the capillary membrane.