Publications

• Cloning and characterization of two human polyspecific organic cation transporters.

  Gorboulev V., Ulzheimer J.C., Akhoundova A., Ulzheimer-Teuber I., Karbach U., Quester S., Baumann C., Lang F., Busch A.E., Koepsell H.

  Previously we cloned a polyspecific transporter from rat (rOCT1) that is expressed in renal proximal tubules and hepatocytes and mediates electrogenic uptake of organic cations with different molecular structures. Recently a homologous transporter from rat kidney (rOCT2) was cloned but not charact ... >> More

  Previously we cloned a polyspecific transporter from rat (rOCT1) that is expressed in renal proximal tubules and hepatocytes and mediates electrogenic uptake of organic cations with different molecular structures. Recently a homologous transporter from rat kidney (rOCT2) was cloned but not characterized in detail. We report cloning and characterization of two homologous transporters from man (hOCT1 and hOCT2) displaying approximately 80% amino acid identity to rOCT1 and rOCT2, respectively. Northern blots showed that hOCT1 is mainly transcribed in liver, while hOCT2 is found in kidney. Using in situ hybridization and immunohistochemistry, expression of hOCT2 was mainly detected in the distal tubule where the transporter is localized at the luminal membrane. After expression in Xenopus laevis oocytes, hOCT1 and hOCT2 mediate tracer influx of N-1-methylnicotinamide (NMN), tetraethylammonium (TEA), and 1-methyl-4-phenylpyridinium (MPP). For cation transport by hOCT2 apparent K(m) and K(i) values were determined in tracer flux measurements. In addition, electrical measurements were performed with voltage-clamped oocytes. Similar to rOCT1, cation transport by hOCT2 was pH independent, electrogenic, and polyspecific; however, the cation specificity was different. In voltage-clamped hOCT2-expressing oocytes, inward currents were induced by superfusion with MPP, TEA, choline, quinine, d-tubocurarine, pancuronium, and cyanine863. Cation transport in distal tubules is indicated for the first time. Here hOCT2 mediates the first step in cation reabsorption. hOCT1 may participate in hepatic excretion of organic cations. << Less

  DNA Cell Biol. 16:871-881(1997) [PubMed] [EuropePMC]

  This publication is cited by 1 other entry.

• Electrogenic properties and substrate specificity of the polyspecific rat cation transporter rOCT1.

  Busch A.E., Quester S., Ulzheimer J.C., Waldegger S., Gorboulev V., Arndt P., Lang F., Koepsell H.

  The previously cloned rat cation transporter rOCT1 detected in renal proximal tubules and hepatocytes (Gründemann, D., Gorboulev, V., Gambaryan, S., Veyhl, M., and Koepsell, H. (1994) Nature 372, 549-552) was expressed in Xenopus oocytes, and transport properties were analyzed using tracer uptake ... >> More

  The previously cloned rat cation transporter rOCT1 detected in renal proximal tubules and hepatocytes (Gründemann, D., Gorboulev, V., Gambaryan, S., Veyhl, M., and Koepsell, H. (1994) Nature 372, 549-552) was expressed in Xenopus oocytes, and transport properties were analyzed using tracer uptake studies and electrophysiological measurements. rOCT1 induced highly active transport of a variety of cations, including the classical substrates for cation transport, such as N-1-methylnicotinamide, 1-methyl-4-phenylpyridinium (MPP), and tetraethylammonium (TEA), but also the physiologically important choline. In oocytes rOCT1 also mediated efflux of MPP, which could be trans-stimulated by MPP and TEA. Cation transport via rOCT1 was electrogenic. In voltage-clamped oocytes, transport of TEA and choline via rOCT1 produced inwardly directed currents, which were independent of extracellular ion composition or pH. The choline- and TEA-induced currents were voltage-dependent at nonsaturating concentrations, and the apparent affinity of these cations was decreased at depolarized voltages. Other substrates transported by rOCT1 were the polyamines spermine and spermidine. Interestingly, the previously described potent inhibitors of rOCT1, cyanine 863, quinine, and D-tubocurarine were substrates themselves. The data indicate that rOCT1 is an effective transport system that is responsible for electrogenic uptake of a wide variety of organic cations into epithelial cells of renal proximal tubules and hepatocytes. << Less

  J. Biol. Chem. 271:32599-32604(1996) [PubMed] [EuropePMC]

  This publication is cited by 1 other entry.

• Interaction of cations, anions, and weak base quinine with rat renal cation transporter rOCT2 compared with rOCT1.

  Arndt P., Volk C., Gorboulev V., Budiman T., Popp C., Ulzheimer-Teuber I., Akhoundova A., Koppatz S., Bamberg E., Nagel G., Koepsell H.

  The rat organic cation transporter (rOCT)-2 was characterized by electrical and tracer flux measurements compared with rOCT1. By applying choline gradients to voltage-clamped Xenopus oocytes expressing rOCT2, potential-dependent currents could be induced in both directions. Tracer flux measurement ... >> More

  The rat organic cation transporter (rOCT)-2 was characterized by electrical and tracer flux measurements compared with rOCT1. By applying choline gradients to voltage-clamped Xenopus oocytes expressing rOCT2, potential-dependent currents could be induced in both directions. Tracer flux measurements with seven organic cations revealed similar Michaelis-Menten constant values for both transporters, with the exception of guanidine. In parallel experiments with rOCT2 and rOCT1, inhibition of tetraethylammonium transport by 12 cations, 2 weak bases, corticosterone, and the anions para-amminohippurate, alpha-ketoglutarate, and probenecid was characterized. The IC(50) values of many inhibitors were similar for both transporters, whereas others were significantly different. Mepiperphenidol and O-methylisoprenaline showed an approximately 70-fold lower and corticosterone a 38-fold higher affinity for rOCT2. With the use of these inhibitors together with previous information on cation transporters, experimental protocols are proposed to dissect out the individual contributions of rOCT2 and rOCT1 in intact proximal tubule preparations. Inhibition experiments at different pH levels strongly suggest that the weak base quinine passively permeates the plasma membrane at physiological pH and inhibits rOCT2 from the intracellular side. << Less

  Am. J. Physiol. 281:F454-F468(2001) [PubMed] [EuropePMC]

  This publication is cited by 3 other entries.