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A Reevaluation of Substrate Specificity of the Rat Cation Transporter rOCT1

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Nagel,  Georg
Department of Biophysical Chemistry, Max Planck Institute of Biophysics, Max Planck Society;
Johann-Wolfgang-Goethe-Universität, Biozentrum, FB 15, 60439 Frankfurt am Main, Germany;

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Friedrich,  Thomas
Department of Biophysical Chemistry, Max Planck Institute of Biophysics, Max Planck Society;

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Bamberg,  Ernst
Department of Biophysical Chemistry, Max Planck Institute of Biophysics, Max Planck Society;
Johann-Wolfgang-Goethe-Universität, Biozentrum, FB 15, 60439 Frankfurt am Main, Germany;

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Citation

Nagel, G., Volk, C., Friedrich, T., Ulzheimer, J. C., Bamberg, E., & Koepsell, H. (1997). A Reevaluation of Substrate Specificity of the Rat Cation Transporter rOCT1. The Journal of Biological Chemistry, 272(51), 31953-31956. doi:10.1074/jbc.272.51.31953.


Cite as: http://hdl.handle.net/21.11116/0000-0007-6490-5
Abstract
The substrate specificity of the previously cloned rat cation transporter rOCT1, which is expressed in kidney, liver, and small intestine, was reevaluated. rOCT1 is the first member of a new protein family comprising electrogenic and polyspecific cation transporters that transport hydrophilic cations like tetraethylammonium, choline, and monoamine neurotransmitters. Previous electrical measurements suggested that cations like quinine, quinidine, and cyanine 863, which have been classified as type 2 cations in the liver, are also transported by rOCT1, since they may induce inward currents in rOCT1 expressingXenopus oocytes (Busch, A. E., Quester, S., Ulzheimer, J. C., Waldegger, S., Gorboulev, V., Arndt, P., Lang, F., and Koepsell, H. (1996) J. Biol. Chem. 271, 32599–32604). Tracer flux measurements with oocytes and with stably transfected human embryonic kidney cells showed that [3H]quinine and [3H]quinidine are not transported by rOCT1. The voltage dependence observed for the quinine- or quinidine-induced inward currents in rOCT1-expressing oocytes, and tracer efflux measurements indicate that the inward currents by type 2 cations are generated by the inhibition of electrogenic efflux of transported type 1 cations. Therefore, rOCT1 cannot contribute to transport of type 2 cations in the liver and the hepatic transporter for type 2 cations remains to be identified.