Hypertonicity enhances GABA uptake by cultured rat retinal capillary endothelial cells |
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Authors: | Yahara Tohru Tachikawa Masanori Akanuma Shin-ichi Hosoya Ken-ichi |
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Institution: | Department of Pharmaceutics, Graduate School of Medicine and Pharmaceutical Sciences, University of Toyama, Sugitani, Toyama, Japan. |
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Abstract: | 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 (K(m)) constant of 3.5 mM under isotonic conditions and K(m) 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. |
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