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Related Experiment Videos

Functional characterization of mouse cation transporter mOCT2 compared with mOCT1.

Mari Kakehi1, Noriko Koyabu, Takanori Nakamura

  • 1Department of Medico-Pharmaceutical Sciences, Graduate School of Pharmaceutical Sciences, Kyushu University, 3-1-1 Maidashi, Higashi-ku, Fukuoka 812-8582, Japan.

Biochemical and Biophysical Research Communications
|August 15, 2002
PubMed
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Mouse organic cation transporter 2 (mOCT2) shares functional similarities with mOCT1, including substrate affinity and pH sensitivity. However, mOCT2 exhibits weaker inhibition by certain organic cations compared to mOCT1.

Area of Science:

  • Pharmacology
  • Molecular Biology
  • Biochemistry

Background:

  • Organic cation transporters (OCTs) play crucial roles in the absorption, distribution, metabolism, and excretion (ADME) of various endogenous and exogenous compounds.
  • Understanding the specific functions of OCT family members, such as mouse OCT1 (mOCT1) and OCT2 (mOCT2), is essential for predicting drug disposition and potential drug-drug interactions.

Purpose of the Study:

  • To characterize and compare the functional properties of mouse organic cation transporter 2 (mOCT2) with those of mOCT1.
  • To investigate the substrate specificity, kinetic parameters, and inhibition profiles of mOCT1 and mOCT2.

Main Methods:

  • Functional characterization of mOCT1 and mOCT2 using Xenopus laevis oocytes expressing the respective cRNAs.
  • Uptake assays were performed using radiolabeled substrates, including [(3)H]1-methyl-4-phenylpyridinium ([(3)H]MPP(+)) and [(14)C]tetraethylammonium.

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  • Kinetic analysis (Michaelis-Menten kinetics) and inhibition studies with various organic cations were conducted.

    • Main Results:

    • Both mOCT1 and mOCT2 mediated saturable uptake of [(3)H]MPP(+), with similar Michaelis constants (K(t)) of 10 µM for mOCT1 and 24 µM for mOCT2.
    • mOCT2 also transported [(14)C]tetraethylammonium with a K(t) of 36 µM, comparable to mOCT1.
    • Uptake via both transporters was sensitive to extracellular K(+) concentration and acidic pH.
    • Several organic cations, including quinine and cimetidine, inhibited [(3)H]MPP(+) uptake by both transporters, but generally with lower potency against mOCT2 compared to mOCT1.

    Conclusions:

    • Mouse OCT2 exhibits functional similarities to mOCT1 regarding substrate affinity for MPP(+) and tetraethylammonium, membrane potential dependency, and pH sensitivity.
    • Despite these similarities, mOCT2 demonstrates distinct differences in its interaction with certain organic cation inhibitors, showing weaker inhibition compared to mOCT1.
    • These findings highlight the nuanced functional differences between mOCT1 and mOCT2, which may have implications for their roles in vivo and in drug development.