Acidosis induces hyperpermeability in caco-2bbe cultured intestinal epithelial monolayers. Menconi, Michael J., Andrew L. Salzman, Naoki Unno, Robert M. Ezzell, Diane M. Casey, Daniel A. Brown, Yoshifumi Tsuji, and Mitchell P. Fink. Departments of Surgery and Anesthesiology, Beth Israel Hospital and Harvard Medical School, Boston, MA 02215 and Department of Surgery, Massachusetts General Hospital and Harvard Medical School, Boston, MA 02215
APStracts 3:0238G, 1996.
We previously demonstrated that ileal mucosal acidosis in pigs reversibly increases intestinal permeability to hydrophilic macromolecules, even in the absence of tissue hypoxia [Salzman et al., Am. J. Physiol. 266 (Gastrointest. Liver Physiol. 29): G633 -G646]. In an effort to further explore the mechanism(s) underlying this phenomenon, we examined the effect of acidic pH on the permeability characteristics of cultured Caco-2BBe (human intestinal epithelial) cells grown as monolayers on permeable supports. Permeability was determined by measuring the mucosal-to-basolateral flux of fluorescein disulfonic acid (FS; MW=478 Da), fluorescein -labelled dextran (FD4; average MW=4 kDa), or 3H-mannitol. Incubation of monolayers under hypercarbic conditions or with acidified bicarbonate-free medium significantly increased permeability to FS, FD4, and mannitol in a manner dependent on both time and pH. Incubation in medium at pH 5.43 for 24 h increased the release of LDH and decreased the intensity of staining with calcein-AM, findings which are indicative of plasma membrane injury; nevertheless, the percentage of nonviable cells was not increased. Ultrastructural analyses revealed evidence of increased paracellular trafficking of horseradish peroxidase following incubation of monolayers under acidic conditions. Fluorescence confocal microscopy and temperature studies demonstrated that incubation at pH 5.43 induced an increase in both the intracellular uptake of FD4 and the activation energy for FS permeation across Caco-2BBe monolayers, respectively, suggesting increased transcellular permeation. Exposure to acidic conditions also decreased cellular levels of ATP. We conclude that acidosis increases both paracellular and transcellular permeability to hydrophilic macromolecules and leads to depletion of ATP. 

Received 23 June 1995; accepted in final form 30 October 1996.
APS Manuscript Number G270-5.
Article publication pending Am. J. Physiol. (Gastrointest. Liver
Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 13 November 1996