FLUID ABSORPTION IN ISOLATED-PERFUSED COLONIC CRYPTS

A spatial segregation of ion transport processes between crypt and sur face epithelial cells is well-accepted and integrated into physiologic al and pathophysiological paradigms of small and large intestinal func tion: Absorptive processes are believed to be located in surface (and villous) cells, whereas secretory processes are believed to be present in crypt cells. Validation of this model requires direct determinatio n of fluid movement in intestinal crypts. This study describes the ada ptation of techniques from renal tubule microperfusion to hand-dissect and perfuse single, isolated crypts from rat distal colon to measure directly fluid movement. Morphologic analyses of the isolated crypt pr eparation revealed no extraepithelial cellular elements derived from t he lamina propria, including myofibroblasts. In the basal state, crypt s exhibited net fluid absorption (mean net fluid movement = 0.34+/-0.0 1 nl . mm(-1). min(-1)), which was Na+ and partially HCO3- dependent. Addition of 1 mM dibutyryl-cyclic AMP, 60 nM vasoactive intestinal pep tide, or 0.1 mM acetylcholine to the bath (serosal) solution reversibl y induced net fluid secretion (net fluid movement approximate to -0.35 +/-0.01 . nl . mm(-1). min(-1)). These observations permit speculation that absorption is a constitutive transport function in crypt cells a nd that secretion by crypt cells is regulated by one or more neurohumo ral agonists that are released in situ from lamina propria cells. The functional, intact polarized crypt described here that both absorbs an d secretes will permit future studies that dissect the mechanisms that govern fluid and electrolyte movement in the colonic crypt.