title: Uptake of L-carnitine by a human intestinal epithelial cell line, Caco-2.
abstract: OBJECTIVE
  The mechanism of intestinal uptake of L-carnitine is controversial. The aim of this study was to clarify the mechanism and regulation of L-carnitine uptake.
  
  
  METHODS
  Uptake of [3H]-L-carnitine was measured across the apical membrane of confluent monolayers of Caco-2 cells.
  
  
  RESULTS
  [3H]-L-carnitine uptake was linear and appreciable for up to 7 minutes with minimal metabolic alteration, was temperature- and Na(+)-(but not pH-) dependent, and included a saturable component with an apparent Michaelis constant of 45.5 +/- 6.5 mumol/L and a maximum velocity of 83.5 +/- 5.6 nmol.mg protein-1.5 min-1. Unlabeled L-carnitine and its structurally related analogues significantly (P < 0.01) inhibited [3H]-L-carnitine uptake, whereas unrelated compounds were ineffective. L-Carnitine uptake was also energy-dependent, being significantly (P < 0.01) inhibited by metabolic inhibitors. Our results also suggested that a calmodulin- but not a protein kinase C- or protein kinase A-mediated pathway plays a role in regulating L-carnitine uptake by Caco-2 cells.
  
  
  CONCLUSIONS
  L-carnitine uptake by intestinal epithelial cells (Caco-2) involves a carrier-mediated system that is temperature-, Na(+)-, and energy-dependent and seems to be under the regulation of a calmodulin-mediated pathway.
authors.affiliation: Department of Pediatrics, University of California College of Medicine, Irvine, USA.
authors.forename: E
authors.initials: E
authors.lastname: McCloud
authors.forename: T Y
authors.initials: TY
authors.lastname: Ma
authors.forename: K E
authors.initials: KE
authors.lastname: Grant
authors.forename: R K
authors.initials: RK
authors.lastname: Mathis
authors.forename: H M
authors.initials: HM
authors.lastname: Said
mesh_terms: D001692:Biological Transport; D018938:Caco-2 Cells; D002331:Carnitine / Q000378:metabolism*; D006801:Humans; D007413:Intestinal Mucosa / Q000378:metabolism*; D015398:Signal Transduction; D013696:Temperature; D014316:Tritium
chemical_list: D014316:Tritium; D002331:Carnitine