Na(+)/dicarboxylate cotransporter 3
succinate transmembrane transporter activity
Glutathione is a low-affinity substrate of the human sodium-dependent dicarboxylate transporter.
<h4>Background/aims</h4>During a single pass through the kidneys, more than 80% of glutathione (GSH) is excreted, indicating not only glomerular filtration, but also tubular secretion. The first step in tubular secretion is the uptake of a substance across the basolateral membrane of proximal tubule cells by sodium-dependent and -independent transporters. Due to the dicarboxylate-like structure, we postulated that GSH uptake across the basolateral membrane is mediated by the sodium-dependent dicarboxylate transporter 3 (NaDC3).<h4>Methods</h4>Tracer uptake and electrophysiologic measurements using a two-electrode voltage clamp device were performed in Xenopus laevis oocytes expressing the human (h)NaDC3.<h4>Results</h4>Uptake of succinate, the reference substrate of hNaDC3, was inhibited by GSH in a dose-dependent manner with an IC50 of 1.88 mM. GSH evoked potential-dependent inward currents, which were abolished under sodium-free conditions. At -60 mV, GSH currents showed saturation kinetics with a KM of 1.65 mM.<h4>Conclusion</h4>hNaDC3 present at the basolateral membrane of proximal tubule cells mediates sodium-dependent GSH uptake. The kinetic data show that NaDC3 is a low-affinity GSH transporter.