Vol. 281, Issue 2, F273-F279, August 2001
Independent organic cation transport activity
of Na+-L-carnitine cotransport system in
LLC-PK1 cells
Shuichi
Ohnishi,
Hideyuki
Saito,
Atsuko
Fukada, and
Ken-Ichi
Inui
Department of Pharmacy, Kyoto University Hospital, Faculty of
Medicine, Kyoto University, Kyoto 606-8507, Japan
We investigated expression of the
Na+-L-carnitine cotransport system and its role
in transport of tetraethylammonium in a kidney epithelial cell line,
LLC-PK1. L-Carnitine uptake in the
LLC-PK1 cells was markedly stimulated in the presence of
Na+. The uptake was saturable, with Michaelis constant and
maximal uptake velocity values of 7.8 µM and 153.7 pmol · mg
protein
1 · 15 min1, respectively.
Cationic drugs such as tetraethylammonium, cimetidine, and quinidine
inhibited L-carnitine uptake. The basolateral-to-apical transport of [14C]tetraethylammonium was enhanced
markedly in the presence of an H+ gradient on the apical
side at a pH of 5.9. Under the conditions in which
Na+/L-carnitine cotransport activity was
saturable by the addition of 100 µM L-carnitine to the
apical-side medium, the basolateral-to-apical transcellular transport
of [14C]tetraethylammonium was unaffected. These results
suggested that the Na+-L-carnitine
cotransporter is expressed in the apical membranes of
LLC-PK1 cells, and is not responsible for efflux of
tetraethylammonium from the cells. Transport of tetraethylammonium
appeared to be mediated predominantly by an H+/organic
cation antiporter in the apical membranes.
L-carnitine transporter; organic cation transporter; kidney epithelial cell line
