Uptake of L-carnitine by a human intestinal epithelial cell line, Caco-2.
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.
McCloud
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Department of Pediatrics, University of California College of Medicine, Irvine, USA.
Ma
T Y
TY
Grant
K E
KE
Mathis
R K
RK
Said
H M
HM
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
D014316:Tritium; D002331:Carnitine