Mechanism of electrogenic cation transport by the cloned organic cation transporter 2 from rat.

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Budiman T, Bamberg E, Koepsell H, Nagel G

Mechanism of electrogenic cation transport by the cloned organic cation transporter 2 from rat.

J Biol Chem. 2000 Sep 22;275(38):29413-20.

PubMed ID

10889205 [ View in PubMed

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Abstract

The organic cation transporter 2 (OCT2) is expressed in plasma membranes of kidney and brain. Its transport mechanism and substrates are debated. We studied substrate-induced changes of electrical current with the patch clamp technique after expression of rat OCT2 in oocytes. Activation of current, corresponding to efflux, was observed for small organic cations, e.g. choline. In contrast, the bigger cations quinine and tetrabutylammonium elicited no change in current. However, transport of choline could be inhibited by applying quinine or tetrabutylammonium to the cytoplasmic side. Inhibition of organic cation efflux by quinine was competitive with substrates. Quinine at the inside also inhibited substrate influx from the outside. Current-voltage analysis showed that both maximal turnover and apparent affinity to substrates are voltage-dependent. Substrate-induced currents with organic cations on both membrane sides reversed as predicted from the Nernst potential. Our results clearly identify the electrochemical potential as driving force for transport at neutral pH and exclude an electroneutral H(+)/organic cation(+) exchange. We suggest the existence of an electroneutral organic cation(+) exchange and propose a model for a carrier-type transport mechanism.

DrugBank Data that Cites this Article

Drug Transporters

Drug	Transporter	Kind	Organism	Pharmacological Action	Actions
Choline	Solute carrier family 22 member 2	Protein	Humans	Unknown	Substrate Inhibitor	Details
Choline salicylate	Solute carrier family 22 member 2	Protein	Humans	Unknown	Substrate Inhibitor	Details