REGULATORY VOLUME INCREASE AFTER HYPERTONICITY-INTESTINAL-PEPTIDE-INDUCED OR VASOACTIVE-INTESTINAL-PEPTIDE-INDUCED CELL-VOLUME DECREASE IN SMALL-INTESTINAL CRYPTS IS DEPENDENT ON NA+-K+-2CL- COTRANSPORT

The volume of intact crypts isolated from guinea-pig small intestine has been measured to assess the capacity of the cells to regulate their volume after hypertonic shock or vasoactive-intestinal-peptide (VIP)-induced shrinkage. Crypts exposed to anisotonic medium initially behave as perfect osmometers. Continued exposure to a hypertonic (400 mosmol/l) medium was followed by regulatory volume increase (RVI), which led to complete volume recovery in about 20 min. VIP produced a volume reduction, attributed to KCl loss through channels activated by the secretagogue, without any recovery during exposure to the polypeptide. Removal of VIP led to an increase of cellular volume towards control levels. This volume recovery after secretagogue-induced shrinkage is termed SVI. Both RVI and SVI were abolished by removal of Na+ or Cl- from the bathing solution, by addition of the loop diuretic bumetanide (1 muM), but not by addition of ethylisopropylamiloride (10 muM) or amiloride (1 mM). Cell shrinkage was also observed when tonicity was increased by addition of 100 mM NaCl or 200 MM D-mannitol, but RVI was seen only when NaCl was the added osmolyte. The ion dependence, pharmacological sensitivity and thermodynamic considerations of these effects are consistent with the operation of a Na+-K+-2Cl- cotransport mechanism activated by cell shrinkage and the secretagogue action of VIP.