NOVEL TRANSPORT-PROPERTIES OF COLONIC CRYPT CELLS - FLUID ABSORPTION AND CL-DEPENDENT NA-H EXCHANGE

Colonic ion transport is heterogeneous including the long-accepted spa tial separation of absorptive and secretory processes between surface and crypt cells. We recently described the isolation of individual cry pts from the rat distal colon that were studied using microperfusion t echnology. Na-dependent fluid absorption was consistently demonstrated in these crypts during perfusion with a Ringer-like solution; dibutyr yl cyclic AMP, VIP and acetylcholine, when added to the bath solution, all induced net fluid secretion. As several morphologic techniques, i ncluding immunocytochemistry, failed to provide evidence for the prese nce of myofibroblasts in the isolated crypt preparation, we propose th at a Na-dependent absorptive process is a constitutive transport mecha nism in crypt cells, while secretory processes are regulated by the re lease of one or more neurohumoral agonists from lamina propria cells i ncluding myofibroblasts. The mechanism of Na-dependent fluid movement was also studied by determining [H] gradient stimulation of Na-22 upta ke in isolated apical membrane vesicles (AMV) from crypt cells. In con trast to Na-H exchange in surface cell AMV, Na-H exchange in crypt cel ls is Cl-dependent. Intracellular pH determined in crypt cells using v ideo-imaging fluorescence microscopy established that the response to an acid load requires both lumen Na and Cl. As a result, these studies have identified a novel Cl-dependent Na-H exchange in crypt AMV that may mediate apical membrane Na uptake and regulate pHi. (C) 1997 Elsev ier Science Inc.