title: Na(+)-dependent fluid absorption in intact perfused rat colonic crypts.
abstract: OBJECTIVE
  The traditional paradigm of fluid movement in the mammalian colon is that fluid absorption and secretion are present in surface and crypt cells, respectively. We have recently demonstrated Na(+)-dependent fluid absorption in isolated crypts that are devoid of neurohumoral stimulation. We now explore the mechanism of Na(+)-dependent fluid absorption in isolated rat colonic crypts.
  
  
  METHODS
  Net fluid absorption was determined using microperfusion techniques and methoxy[(3)H]inulin with ion substitutions and transport inhibitors.
  
  
  RESULTS
  Net fluid absorption was reduced but not abolished by substitution of either N-methyl-D-glucamine- Cl(-) or tetramethylammonium for Na(+) and by lumen addition of 5-ethylisopropyl amiloride, an amiloride analogue that selectively inhibits Na(+)-H(+) exchange. Net fluid absorption was also dependent on lumen Cl(-) because removal of lumen Cl(-) significantly (P < 0.001) reduced net fluid absorption. DIDS at 100 micromol/L, a concentration at which DIDS is an anion exchange inhibitor, minimally reduced net fluid absorption (P < 0.05). In contrast, either 500 micromol/L DIDS, a concentration at which DIDS is known to act as a Cl(-) channel blocker, or 10 micromol/L NPPB, a Cl(-) channel blocker, both substantially inhibited net fluid absorption (P < 0.001). Finally, both the removal of bath Cl(-) and addition of bath bumetanide, an inhibitor of Na-K-2Cl cotransport and Cl(-) secretion, resulted in a significant increase in net fluid absorption.
  
  
  CONCLUSIONS
  (1) Net Na(+)-dependent net fluid absorption in the isolated colonic crypt represents both a larger Na(+)-dependent absorptive process and a smaller secretory process; and (2) the absorptive process consists of a Na(+)-dependent, HCO(3)(-)-independent process and a Na(+)-independent, Cl(-)-dependent, HCO(3)(-)-dependent process. Fluid movement in situ represents these transport processes plus fluid secretion induced by neurohumoral stimulation.
authors.affiliation: Department of Surgery, Yale University, New Haven, Connecticut, USA.
authors.forename: J P
authors.initials: JP
authors.lastname: Geibel
authors.forename: V M
authors.initials: VM
authors.lastname: Rajendran
authors.forename: H J
authors.initials: HJ
authors.lastname: Binder
mesh_terms: D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid / Q000494:pharmacology; D000818:Animals; D001639:Bicarbonates / Q000378:metabolism; D002712:Chlorides / Q000378:metabolism; D003106:Colon / Q000378:metabolism*; D005731:Ganglionic Stimulants / Q000494:pharmacology; D005971:Glutamates / Q000494:pharmacology; D066298:In Vitro Techniques; D007408:Intestinal Absorption / Q000502:physiology*; D007444:Inulin / Q000493:pharmacokinetics; D007552:Isotonic Solutions / Q000493:pharmacokinetics; D008297:Male; D010477:Perfusion; D000644:Quaternary Ammonium Compounds / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D000077331:Ringer's Solution; D012964:Sodium / Q000378:metabolism*; D017923:Sodium-Hydrogen Exchangers / Q000378:metabolism; D014316:Tritium
chemical_list: D001639:Bicarbonates; D002712:Chlorides; D005731:Ganglionic Stimulants; D005971:Glutamates; D007552:Isotonic Solutions; D000644:Quaternary Ammonium Compounds; D017923:Sodium-Hydrogen Exchangers; D014316:Tritium; C014574:gamma-glutamylmethylamide; D000077331:Ringer's Solution; D007444:Inulin; D012964:Sodium; C027917:tetramethylammonium; D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid