Function, expression, and characterization of the serotonin transporter in the native human intestine.
The enteric serotonin transporter (SERT) plays a critical role in modulating serotonin availability and thus has been implicated in the pathogenesis of various intestinal disorders. To date, SERT expression and function in the human intestine have not been investigated. Current studies were designed to characterize the function, expression, distribution, and membrane localization of SERT in the native human intestine. Real-time PCR studies showed relatively higher SERT mRNA expression in the human small intestine compared with colon (ileum >> duodenum >> jejunum). Northern blot analysis revealed three mRNA hybridizing species encoding SERT (3.0, 4.9, and 6.8 kb) in the human ileum. Consistent with SERT mRNA expression, SERT immunostaining was mainly detected in the epithelial cells of human duodenal and ileal resected tissues. Notably, SERT expression was localized predominantly to the apical and intracellular compartments and was distributed throughout the crypt-villus axis. Immunoblotting studies detected a prominent protein band ( approximately 70 kDa) in the ileal apical plasma membrane vesicles (AMVs) isolated from mucosa obtained from organ-donor intestine. Functional studies showed that uptake of [(3)H]serotonin (150 nM) in human ileal AMVs was 1) significantly increased in the presence of both Na(+) and Cl(-); 2) inhibited ( approximately 50%) by the neuronal SERT inhibitor, fluoxetine (10 microM) and by unlabeled 5-HT; and 3) exhibited saturation kinetics indicating the presence of a carrier-mediated process. Our studies demonstrated differential expression of SERT across various regions of the human intestine and provide evidence for the existence of a functional SERT capable of removing intraluminal serotonin in human ileal epithelial cells.
Gill
Ravinder K
RK
Research Assistant Professor, Univ. of Illinois at Chicago, Jesse Brown V. A. Medical Center, Medical Research Service (600/151 820 South Damen Ave., Chicago, IL 60612. rgill@uic.edu).
Pant
Nitika
N
Saksena
Seema
S
Singla
Amika
A
Nazir
Talat M
TM
Vohwinkel
Lisa
L
Turner
Jerrold R
JR
Goldstein
Jay
J
Alrefai
Waddah A
WA
Dudeja
Pradeep K
PK
D015152:Blotting, Northern; D002462:Cell Membrane / Q000378:metabolism; D002712:Chlorides / Q000378:metabolism; D004847:Epithelial Cells / Q000187:drug effects / Q000378:metabolism*; D005455:Fluorescent Antibody Technique; D005473:Fluoxetine / Q000494:pharmacology; D006801:Humans; D007413:Intestinal Mucosa / Q000378:metabolism*; D007422:Intestines / Q000187:drug effects; D007700:Kinetics; D016133:Polymerase Chain Reaction; D012333:RNA, Messenger / Q000378:metabolism; D012701:Serotonin / Q000378:metabolism*; D050486:Serotonin Plasma Membrane Transport Proteins / Q000235:genetics / Q000378:metabolism*; D017367:Selective Serotonin Reuptake Inhibitors / Q000494:pharmacology; D012964:Sodium / Q000378:metabolism; D014316:Tritium
D002712:Chlorides; D005473:Fluoxetine; D012333:RNA, Messenger; D012701:Serotonin; D050486:Serotonin Plasma Membrane Transport Proteins; D017367:Selective Serotonin Reuptake Inhibitors; D012964:Sodium; D014316:Tritium; C493230:SLC6A4 protein, human