The absorption of phenolsulfonphthalein (phenol red) was used as a measure in vivo of intestinal permeability in anesthetized rats. A chelating agent, sodium ethylencdiaminetetraacetate (NaEDTA), placed in the lumen evoked a fivefold increase in membrane permeability; at the same time the mucosal content of magnesium and calcium decreased significantly. Making either magnesium or calcium available to the luminal surface of the membrane in isotonic solution restored normal permeability and brought the cation contents above the original levels. Electron micrographs of tissues treated in vivo with NaEDTA revealed (a) rounded swellings on the microvilli in the area of the junctional complexes between adjacent epithelial cells, (b) widening of intercellular channels particularly in the region of the intermediate junctions (zonulae adhaerentes), and (c) loss of architectural detail in the region of the desmosomes (maculae adhaerentes) with separation of their dense borders. All of these alterations in fine structure could be reversed by in vivo cation replacements which reinstated normal permeability. The implications of these findings on mechanisms of fluid transport across epithelial membranes are discussed, and a working hypothesis for the role of divalent cations in membrane permeability regulation is presented.The ability of the chelating agent sodium ethylenediaminetetraacetate (NaEDTA) to increase the permeability of the intestinal epithelial membrane has now been reported by a number of different laboratories (1-3). The relation of these changes to the magnesium and calcium contents of the membrane was suggested in an earlier report which established the reversibility of the phenomenon (4). The present article utilizes a newly developed method for the simultaneous determination of calcium and magnesium in samples derived from soft tissues, 1 in order to clarify the relationship between the mucosal content of these alkaline-earth cations and the permeability alteration. In addition, electron micrographs are presented which delineate changes in the fine structure of this epithelial tissue during chelation depiction and its attendant increase in permeability. Both permeability and structural alterations could be reversed either partly or completely by treating in vivo with either isotonic MgC12 or CaC12. Therefore it seems likely that the phenomena described are of physiological significance and that their further elucidation may contribute to our understanding of fluid transport across epithelial membranes as well as the nature of molecular forces involved in cell adhesion. METHODSThe Principles of Laboratory Animal Care as promulgated by the National Society for Medical Research were observed during this study. Male 685on May 10, 2018 jcb.rupress.org Downloaded from http://doi.org/10.1083/jcb.32.3.685 Published Online: 1 March, 1967 | Supp Info:Sprague-Dawley rats, 200 300 g in weight, were anesthetized with 40 mg/kg of sodium pentobarbital after having been fasted for 24 hr. The small intestine was div...

The absorption of phenolsulfonphthalein (phenol red) was used as a measure of intestinal permeability in rats anesthetized with sodium pentobarbital. All solutions placed in the intestinal lumen were adjusted to pH 7.0 and 300 mosmoles/liter. When 5 ml of a 1 mm solution of phenol red were placed in either proximal or distal halves of the small intestine the mean hourly absorption was 1.1%. The presence of 25 mm/liter ethylenediaminetetraacetate (EDTA) as the calcium salt did not alter phenol red absorption. With 25 mm/liter NaEDTA in the lumen, the absorption of phenol red was increased tenfold. After NaEDTA had been present for 1 hr, rinsing the lumen produced results which varied with the ionic composition of the rinsing solution. Balanced physiologic saline did not reverse the increased permeability. A CaCl2 rinse produced a permeability intermediate between NaEDTA and control levels. A MgCI2 rinse reinstated normal permeability. It is concluded that magnesium and calcium, loosely bound in the structure of the membrane, regulate the aqueous permeability of the intestinal epithelium.

Characteristically water and chloride ion are absorbed from isotonic saline solutions placed in the in situ jejunal loop of the anesthetized dog. The direction of the water and chloride movement can be reversed by the administration of a cholinergic drug or by the addition of substituted phenols to the isotonic solution bathing the mucosal surface. During such secretion the movement of chloride occurs against a concentration gradient. The transmural electrical potential difference indicates that the lumen is negative with respect to the serosal surface during secretion; thus chloride is also moving against an electrical potential gradient. The calculated concentration of chloride in the fluid moving through the membrane during secretion is higher than the chloride concentration in extracellular fluid which indicates that solvent drag is not responsible for the chloride movement. Therefore active transport of chloride occurs during intestinal secretion.

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