X-ray microanalysis of cell elements in normal and cystic fibrosis jejunum: evidence for chloride secretion in villi.
OBJECTIVE
Cystic fibrosis transmembrane conductance regulator (CFTR) is an adenosine 3',5'-cyclic monophosphate-dependent chloride channel that is defective in cystic fibrosis. The aims of this study were to determine if defective apical chloride secretion in the intestine of patients with cystic fibrosis alters the intracellular electrolyte milieu and to examine the geographical localization of CFTR in the normal intestine.


METHODS
The content of intracellular elements was assessed in cryosections using energy-dispersive x-ray microanalysis, and CFTR was identified by immunocytochemistry using commercially available antibodies.


RESULTS
Cystic fibrosis jejunum had a significantly lower Na+ content, higher K+ and Cl- content, and higher potassium/phosphorus ratio in both villus and crypt regions. Incubation of normal jejunum with the phosphodiesterase inhibitor 3-isobutyl-1-methyl-xanthine (300 mumol/L) resulted in decreased K+ and Cl- content in both crypt and villus regions, indicative of Cl- secretion. CFTR was identified on the surface of normal villus and crypt enterocytes but not in cystic fibrosis samples.


CONCLUSIONS
Defective apical chloride channels in cystic fibrosis result in alterations in the intracellular electrolyte milieu. The microanalysis observations and immunocytochemical studies imply a role for villus enterocytes in human intestinal chloride secretion.
O'Loughlin
E V
EV
Department of Gastroenterology, New Children's Hospital, Westmead, New South Wales, Australia.
Hunt
D M
DM
Bostrom
T E
TE
Hunter
D
D
Gaskin
K J
KJ
Gyory
A
A
Cockayne
D J
DJ
D015056:1-Methyl-3-isobutylxanthine / Q000494:pharmacology; D000818:Animals; D002712:Chlorides / Q000378:metabolism*; D003550:Cystic Fibrosis / Q000378:metabolism*; D019005:Cystic Fibrosis Transmembrane Conductance Regulator / Q000378:metabolism; D004577:Electron Probe Microanalysis; D006801:Humans; D007150:Immunohistochemistry; D007413:Intestinal Mucosa / Q000187:drug effects / Q000378:metabolism*; D007583:Jejunum / Q000187:drug effects / Q000378:metabolism*; D010726:Phosphodiesterase Inhibitors / Q000494:pharmacology; D010758:Phosphorus / Q000378:metabolism; D011188:Potassium / Q000378:metabolism; D011817:Rabbits; D012964:Sodium / Q000378:metabolism
C505032:CFTR protein, human; D002712:Chlorides; D010726:Phosphodiesterase Inhibitors; D019005:Cystic Fibrosis Transmembrane Conductance Regulator; D010758:Phosphorus; D012964:Sodium; D011188:Potassium; D015056:1-Methyl-3-isobutylxanthine