Inhibitors of the gamma-aminobutyric acid transporter 1 (GAT1) do not reveal a channel mode of conduction.
We expressed the gamma-aminobutyric acid (GABA) transporter GAT1 (SLC6A1) in Xenopus laevis oocytes and performed GABA uptake experiments under voltage clamp at different membrane potentials as well as in the presence of the specific GAT1 inhibitors SKF-89976A and NO-711. In the absence of the inhibitors, GAT1 mediated the inward translocation of 2 net positive charges across the plasma membrane for every GABA molecule transported into the cell. This 2:1 charge flux/GABA flux ratio was the same over a wide range of membrane potentials from -110 mV to +10 mV. Moreover, when GABA-evoked (500 microM) currents were measured at -50 and -90 mV, neither SKF-89976A (5 and 25 microM) nor NO-711 (2 microM) altered the 2:1 charge flux/GABA flux ratio. The results are not consistent with previous hypotheses that (i) GABA evokes an uncoupled channel-mediated current in GAT1, and (ii) GAT1 inhibitors block the putative uncoupled current gated by GABA. Rather, the results suggest tight coupling of GAT1-mediated charge flux and GABA flux.
Matthews
Edward
E
Biological Sciences Department, California State Polytechnic University, 3801 West Temple Avenue, Pomona, CA 91768-4032, USA.
Rahnama-Vaghef
Ali
A
Eskandari
Sepehr
S
D000818:Animals; D001693:Biological Transport, Active / Q000187:drug effects / Q000502:physiology; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism*; D005260:Female; D018756:GABA Antagonists / Q000494:pharmacology; D050485:GABA Plasma Membrane Transport Proteins / Q000378:metabolism*; D058805:GABA Uptake Inhibitors; D006801:Humans; D015640:Ion Channel Gating / Q000187:drug effects / Q000502:physiology; D007473:Ion Channels / Q000187:drug effects / Q000378:metabolism*; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D009474:Neurons / Q000187:drug effects / Q000378:metabolism*; D009865:Oocytes; D018408:Patch-Clamp Techniques; D014982:Xenopus laevis; D005680:gamma-Aminobutyric Acid / Q000378:metabolism*
D018756:GABA Antagonists; D050485:GABA Plasma Membrane Transport Proteins; D058805:GABA Uptake Inhibitors; D007473:Ion Channels; D005680:gamma-Aminobutyric Acid