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  • Title: Distinct transport activity of tetraethylammonium from L-carnitine in rat renal brush-border membranes.
    Author: Ohnishi S, Saito H, Fukada A, Inui K.
    Journal: Biochim Biophys Acta; 2003 Jan 31; 1609(2):218-24. PubMed ID: 12543384.
    Abstract:
    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 (K(m)=21 microM) 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.
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