Functional studies of in vitro rat distal colon before and after restitution

Epithelial injury occurs in many acute and chronic diseases of the colon and from simple mechanical and chemical injury in the normal colon. Because epithelial repair is so important, we developed a highly reproducible, entirely in vitro model of restitution in rat distal colon.

The muscosal surface of colon mounted in Ussing chambers was exposed to 1.5 mol/L NaCl (hypertonic saline, HS) for 10 minutes. Transepithelial potential difference, electrical resistance, and short-circuit current were used to measure return of electrophysiologic characteristics of the tissue during recovery from injury. Recovery of the barrier to transepithelial movement of large molecules was assessed by measuring mannitol and inulin permeability. Na+ and Cl- absorption and forskolin-induced Cl- secretion were used as indicators of functional recovery of the colonic mucosa after HS injury. Morphologic evaluation of tissues was performed by light microscopy and transmission electron microscopy.

HS treatment caused marked increases in mannitol and inulin permeability together with exfoliation of colonocytes from the surface and upper crypts, leaving long stretches of denuded basal lamina. Epithelial continuity was morphologically reestablished in 30 to 60 minutes, concomitant with return of permeability to control levels. Potential difference, electrical resistance, and short-circuit current decreased with injury and then gradually recovered, although not to preinjury level. Net Na+ and Cl- absorptions, present in undamaged tissues at approximately equivalent rates, decreased after restitution. Forskolin-stimulated Cl- secretion, present before injury, was abolished after restitution.

These studies describe a highly reproducible in vitro model of injury and restitution of a fully organized epithelium of rat distal colon. Although morphologic continuity and barrier properties recover after extensive superficial mucosal injury, the surface is repopulated by cells displaying transport properties and ultrastructural characteristics distinct from the surface epithelium of undamaged tissues.