Function of taurine transporter (Slc6a6/TauT) as a GABA transporting protein and its relevance to GABA transport in rat retinal capillary endothelial cells.
The purpose of this study was to identify the uptake mechanism of gamma-aminobutyric acid (GABA) via taurine transporter (Slc6a6/TauT) and its relationship with GABA transport at the inner BRB. Rat Slc6a6/TauT-transfected HeLa cells exhibited Na(+)-, Cl(-)-, and concentration-dependent [3H]GABA uptake with a Km of 1.5 mM. Taurine, beta-alanine, and GABA markedly inhibited Slc6a6/TauT-mediated uptake of [3H]GABA. The uptake of [3H]GABA by a conditionally immortalized rat retinal capillary endothelial cell line (TR-iBRB2) was Na(+)-, Cl(-)-, and concentration-dependent with a Km of 2.0 mM. This process was more potently inhibited by substrates of Slc6a6/TauT, taurine and beta-alanine, than those of GABA transporters, GABA and betaine. In the presence of taurine, there was competitive inhibition with a Ki of 74 microM. [3H]Taurine also exhibited competitive inhibition with a Ki of 1.8 mM in the presence of GABA. In conclusion, rat Slc6a6/TauT has the ability to use GABA as a substrate and Slc6a6/TauT-mediated GABA transport appears to be present at the inner BRB.
Tomi
Masatoshi
M
Department of Pharmaceutics, Graduate School of Medicine and Pharmaceutical Sciences, University of Toyama, 2630 Sugitani, Toyama 930-0194, Japan.
Tajima
Ayumi
A
Tachikawa
Masanori
M
Hosoya
Ken-ichi
K
D000818:Animals; D001813:Blood-Retinal Barrier / Q000166:cytology / Q000378:metabolism; D002196:Capillaries / Q000166:cytology*; D042783:Endothelial Cells / Q000166:cytology / Q000378:metabolism*; D006367:HeLa Cells; D006801:Humans; D008562:Membrane Glycoproteins / Q000235:genetics / Q000378:metabolism*; D026901:Membrane Transport Proteins / Q000235:genetics / Q000378:metabolism*; D051381:Rats; D012171:Retinal Vessels / Q000166:cytology* / Q000378:metabolism; D013654:Taurine / Q000378:metabolism; D005680:gamma-Aminobutyric Acid / Q000378:metabolism*; D000099247:Taurine Transporters
D008562:Membrane Glycoproteins; D026901:Membrane Transport Proteins; D013654:Taurine; D005680:gamma-Aminobutyric Acid; D000099247:Taurine Transporters