Hypertonicity Enhances GABA Uptake by Cultured Rat Retinal Capillary Endothelial Cells

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  • YAHARA Tohru
    Department of Pharmaceutics, Graduate School of Medicine and Pharmaceutical Sciences, University of Toyama
  • TACHIKAWA Masanori
    Department of Pharmaceutics, Graduate School of Medicine and Pharmaceutical Sciences, University of Toyama
  • AKANUMA Shin-ichi
    Department of Pharmaceutics, Graduate School of Medicine and Pharmaceutical Sciences, University of Toyama
  • HOSOYA Ken-ichi
    Department of Pharmaceutics, Graduate School of Medicine and Pharmaceutical Sciences, University of Toyama

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We have reported previously that taurine transporter (TauT) mediates γ-aminobutyric acid (GABA) as a substrate in a conditionally immortalized rat retinal capillary endothelial cell line (TR-iBRB2 cells). This study investigates how TauT-mediated GABA transport is regulated in TR-iBRB2 cells under hypertonic conditions. [3H]GABA uptake by TR-iBRB2 cells exposed to 12 h- to 24 h-hypertonic culture medium was significantly greater than that of isotonic culture medium. [3H]GABA uptake by TR-iBRB2 cells was Na+-, Cl−-, and concentration-dependent with a Michaelis-Menten (Km) constant of 3.5 mM under isotonic conditions and Km of 0.324 and 5.48 mM under hypertonic conditions. Under hypertonic conditions, [3H]GABA uptake by TR-iBRB2 cells was more potently inhibited by substrates of TauT, such as taurine and β-alanine, than those of GABA transporters such as GABA, nipecotic acid, and betaine. These results suggest that an unknown high-affinity GABA transport process and TauT-mediated GABA transport are enhanced under hypertonic conditions. In conclusion, hypertonicity enhances GABA uptake by cultured rat retinal capillary endothelial cells.<br>

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