Evidence of luminal phosphatidylcholine secretion in rat ileum.
BACKGROUND
Intestinal mucus not only facilitates substrate absorption, but also forms a hydrophobic, phosphatidylcholine (PC) enriched, barrier against luminal gut contents.


METHODS
For evaluation of the origin of PC in intestinal mucus, we first analyzed the mucus PC in mice with absent biliary phospholipid secretion (mdr2 (-/-) mice) using electrospray ionization (ESI) tandem mass spectroscopy (MS/MS). Second, in situ perfused rat jejunum, ileum and colon were analyzed after i.v. bolus injections of 155 pmol [(3)H]-PC. Additional in vitro experiments were performed with isolated mucosal cells after incubation with the PC precursor [(3)H]-choline.


RESULTS
In mdr2 (-/-) mice and control animals no significant quantitative difference in mucus PC was found, indicating that mucus PC is of intestinal and not biliary origin. In situ perfusion studies detected intestinal secretion of [(3)H]-PC, which was stimulated in presence of 2 mM taurocholate (TC). Secretion rates of [(3)H]-PC were highest in ileum (9.0+/-0.8 fmol h(-1)xcm(-1)), lower in jejunum (4.3+/-0.5) and minimal in colon (0.8+/-0.2). It compares to an intestinal secretion of native PC originating to 64% from bile, 9% from jejunum, 28% from ileum, and 1% from colon. Complementary in vitro studies showed 30-min secretion rates for [(3)H]-PC to be highest in enterocytes from ileum (26.5+/-5.3% of intracellular [(3)H]-PC) and jejunum (19.8+/-2.9%), and significantly lower in colonocytes (8.4+/-1.3%).


CONCLUSIONS
PC in the intestinal mucus originates from secretion by ileal and jejunal enterocytes.
Ehehalt
Robert
R
Department of Internal Medicine IV (Gastroenterology), Heidelberg University Hospital, Bergheimer Strasse 58, 69115 Heidelberg, Germany.
Jochims
Christina
C
Lehmann
Wolf-Dieter
WD
Erben
Gerhard
G
Staffer
Simone
S
Reininger
Cornelia
C
Stremmel
Wolfgang
W
D018435:ATP Binding Cassette Transporter, Subfamily B / Q000172:deficiency / Q000235:genetics / Q000378:metabolism; D018528:ATP-Binding Cassette Transporters / Q000235:genetics / Q000378:metabolism; D000818:Animals; D003106:Colon / Q000378:metabolism; D004847:Epithelial Cells / Q000378:metabolism; D007082:Ileum / Q000378:metabolism*; D007583:Jejunum / Q000378:metabolism; D008297:Male; D051379:Mice; D009093:Mucus / Q000378:metabolism; D010713:Phosphatidylcholines / Q000378:metabolism*; D051381:Rats; D014316:Tritium / Q000378:metabolism
D018435:ATP Binding Cassette Transporter, Subfamily B; D018528:ATP-Binding Cassette Transporters; D010713:Phosphatidylcholines; D014316:Tritium; C095122:multidrug resistance protein 3