Cytosolic ionized Ca21 modulates chemical hypoxia-induced hyperpermeability in intestinal epithelial monolayers

Unno, Naoki, Shozo Baba, and Mitchell P. Fink. Cytosolic ionized Ca21 modulates chemical hypoxia-induced hyperpermeability in intestinal epithelial monolayers. Am. J. Physiol. 274 (Gastrointest. Liver Physiol. 37): G700–G708, 1998.—We reported previously that ATP depletion induced by glycolytic inhibition or cellular hypoxia increases the permeability of intestinal epithelial monolayers [N. Unno, M. J. Menconi, A. L. Salzman, M. Smith, S. Hagen, Y. Ge, R. M. Ezzell, and M. P. Fink. Am. J. Physiol. 270 (Gastrointest. Liver Physiol. 33): G1010–G1021, 1996]. In the present study, we examined the effects of the Ca21 ionophore A-23187 or the intracellular ionized Ca21 concentration ([Ca]i) chelator 1,2-bis(2-aminophenoxy)ethane-N,N,N8,N8-tetraacetic acid (BAPTA)-AM on the permeability of enterocytic (T84) monolayers depleted of ATP by metabolic inhibition. Permeability was assessed by measuring transepithelial electrical resistance and the transepithelial flux of fluorescein sulfonic acid. Although neither A-23187 nor BAPTA-AM affected ATP depletion, A-23187 augmented, whereas BAPTA-AM ameliorated, chemical hypoxia-induced hyperpermeability. BAPTA-AM ameliorated chemical hypoxia-induced cytoskeletal derangements. Monolayers subjected to chemical hypoxia but incubated in a low (i.e., 100 μM) [Ca21] environment showed preservation of junctional integrity, whereas voltage-dependent Ca21 channel blockers (NiCl2 or verapamil) failed to ameliorate chemical hypoxia-induced hyperpermeability. ATP depletion induces hyperpermeability in intestinal epithelial monolayers via a [Ca]i-dependent mechanism. Increased [Ca]i under these conditions reflects leakage of Ca21 from the extracellular milieu via a mechanism unrelated to voltagedependent Ca21 channels.