SEGMENTAL DIFFERENCES ALONG THE CRYPT AXIS IN THE RESPONSE OF CELL-VOLUME TO SECRETAGOGUES OR HYPOTONIC MEDIUM IN THE RAT COLON

VIP caused a decrease in the diameter of rat colonic crypts. This decrease was followed by a volume increase at the middle and the upper third of the crypt, which finally led to an increase of diameter above initial control values. At the fundus only a cell shrinkage was observed. volume increase at the upper parts of the crypt was suppressed by the inhibitor of the Na+-K+-Cl--cotransporter, furosemide. When crypts were exposed to a hypertonic medium, cell shrinkage was followed by a regulatory volume increase at the middle and the upper third of the crypt but not at the fundus region. These results suggest a gradient in the distribution of the Na+-K+-Cl--cotransporter along the crypt axis.