Distinct transport activity of tetraethylammonium from l-carnitine in rat renal brush-border membranes

We investigated the contribution of the Na+/l-carnitine cotransporter in the transport of tetraethylammonium (TEA) by rat renal brush-border membrane vesicles. The transient uphill transport of l-carnitine was observed in the presence of a Na+ gradient. The uptake of l-carnitine was of high affinity...

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Published in:Biochimica et biophysica acta 2003-01, Vol.1609 (2), p.218-224
Main Authors: Ohnishi, Shuichi, Saito, Hideyuki, Fukada, Atsuko, Inui, Ken-ichi
Format: Article
Language:English
Subjects:
4-Chloromercuribenzenesulfonate - pharmacology
Animals
Biological Transport, Active
Brush-border membrane vesicle
Carnitine - antagonists & inhibitors
Carnitine - metabolism
Hydrogen-Ion Concentration
Kidney
Kidney - metabolism
l-Carnitine transporter
Levofloxacin
Male
Microvilli - metabolism
Ofloxacin - pharmacology
Organic Cation Transport Proteins - metabolism
Organic cation transporter
Rats
Rats, Wistar
Sulfhydryl Reagents - pharmacology
Tetraethylammonium - antagonists & inhibitors
Tetraethylammonium - metabolism
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Summary:We investigated the contribution of the Na+/l-carnitine cotransporter in the transport of tetraethylammonium (TEA) by rat renal brush-border membrane vesicles. The transient uphill transport of l-carnitine was observed in the presence of a Na+ gradient. The uptake of l-carnitine was of high affinity (Km=21 μM) and pH dependent. Various compounds such as TEA, cephaloridine, and p-chloromercuribenzene sulfonate (PCMBS) had potent inhibitory effects for l-carnitine uptake. Therefore, we confirmed the Na+/l-carnitine cotransport activity in rat renal brush-border membranes. Levofloxacin and PCMBS showed different inhibitory effects for TEA and l-carnitine uptake. The presence of an outward H+ gradient induced a marked stimulation of TEA uptake, whereas it induced no stimulation of l-carnitine uptake. Furthermore, unlabeled TEA preloaded in the vesicles markedly enhanced [14C]TEA uptake, but unlabeled l-carnitine did not stimulate [14C]TEA uptake. These results suggest that transport of TEA across brush-border membranes is independent of the Na+/l-carnitine cotransport activity, and organic cation secretion across brush-border membranes is predominantly mediated by the H+/organic cation antiporter.
ISSN:0005-2736
0006-3002
1879-2642
DOI:10.1016/S0005-2736(02)00703-4