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.