Kakehi M et al. (2002), Functional characterization of mouse cation tra...

XB-ART-6707

Biochem Biophys Res Commun 2002 Aug 23;2963:644-50. doi: 10.1016/s0006-291x(02)00926-9.

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Functional characterization of mouse cation transporter mOCT2 compared with mOCT1.

Kakehi M , Koyabu N , Nakamura T , Uchiumi T , Kuwano M , Ohtani H , Sawada Y .

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We characterized the function of mouse organic cation transporter OCT2 (TC 2.A.19.1.5) in comparison with that of OCT1 (TC 2.A.19.1.1). Uptake of [(3)H]1-methyl-4-phenylpyridinium ([(3)H]MPP(+)) by Xenopus laevis oocytes injected with mOCT1 (Slc22a1) or mOCT2 (Slc22a2) cRNA was attenuated by an increase of extracellular K(+) concentration and under acidic extracellular conditions. The uptakes of [(3)H]MPP(+) via mOCT1 and mOCT2 were saturable, with similar Michaelis constants (K(t)) of 10 and 24 microM, respectively. mOCT2 also mediated the uptake of [(14)C]tetraethylammonium with a K(t) value of 36 microM, which is similar to that of mOCT1. Quinine, tetraethylammonium, cimetidine, procainamide, choline, and N(')-methylnicotinamide inhibited the uptake of [(3)H]MPP(+) via mOCT1, as well as via mOCT2, and the inhibitory potencies for mOCT1 were comparable to but slightly higher than those for mOCT2. Thus, although the transport properties of mOCT2 are similar to those of mOCT1 in respect to the membrane-potential dependency, pH-sensitivity, and affinities for MPP(+) and tetraethylammonium, several organic cations had weaker inhibitory effects on [(3)H]MPP(+) uptake by mOCT2 than by mOCT1.

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Species referenced: Xenopus laevis
Genes referenced: pou2f1 pou2f2

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	Fig. 1. Effect of buffer ion composition on uptake by X. laevis oocytes injected with water, mOCT1 cRNA or mOCT2 cRNA. Uptake of 1 μM was assayed for 30 min in low-K+ (1 mM) or high-K+ (100 mM) buffer at 18 °C. Data represent means ± SEM of four experiments. Significant differences from values in high-K+ buffer were identified by using Student's t test (*P<0.05).
	Fig. 2. pH-Dependency of uptake by X. laevis oocytes injected with water, mOCT1 cRNA, or mOCT2 cRNA. Uptake of 1 μM was assayed for 30 min at various pH values at 18 °C. Data represent means ± SEM for four experiments. Significant differences from water were identified by using Student's t test (*P<0.05).
	Fig. 3. Concentration dependency of the uptakes of and TEA by mOCT1 and mOCT2. (A and B) Uptake of was assayed for 30 min at 18 °C. (C and D) Uptake of TEA was assayed for 60 min at 18 °C. Data are represented as the OCT-specific uptake calculated by subtracting the uptake in water-injected oocytes from that in OCT-expressing oocytes. Each point represents the mean ±SEM of four experiments. The line was fitted to the Michaelis–Menten equation.
	Fig. 4. Effects of various organic cations on uptake by (A) mOCT1 and (B) mOCT2. Uptake by oocytes was assayed for 30 min at 18 °C in uptake buffer containing 1 μM in the presence of TEA (open circle), procainamide (closed circle), cimetidine (open square), choline (closed square), quinine (open triangle), or NMN (closed triangle). Data represent means ± SEM of four experiments. The line was fitted to the sigmoidal inhibition equation.