Metabolically induced permeability changes across mesothelium and endothelium

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Abstract
The ability of mesothelial and endothelial membranes to influence solute passage into tissue preparations was investigated under in vitro conditions. It is possible by using the Warburg formula for the diffusion of solutes into tissue slices to calculate the concentration of solute bathing the subepithelial tissue when the depth of penetration and tissue activity are known. These conditions were met by selecting an electron acceptor with histochemical properties—the tetrazolium salt, 2-p-iodophenyl-3-p-nitrophenyl-5-phenyl tetrazolium chloride (INT). Quantitative studies with hemidiaphragm demonstrate that the concentration of INT which reaches the inner surface of the mesothelial layer is only 9% of that in the medium. Addition of a redox dye, phenazine methosulfate (PM), increases this value by 6.7 times. (Qualitatively similar results were obtained across mesothelial surfaces of liver and heart, as well as at endothelial surfaces of heart and carotid artery.) The ability of PM to increase permeability is counteracted by malate or succinate, and in turn restored when the latter is blocked with malonate. These results suggest that oxidative metabolism and adenosine triphosphate formation are intimately linked with this phenomenon.