Magnesium and calcium as regulators of intestinal permeability

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Abstract
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.