A GABA transporter operates asymmetrically and with variable stoichiometry.
Membrane currents produced by the expression of a rat GABA transporter (GAT-1) stably transfected into HEK293 cells were characterized with a whole-cell voltage clamp. Three modes of function were identified: ex-gated currents produced by extracellular GABA, in-gated currents produced by intracellular GABA, and uncoupled currents produced in the absence of GABA. The ex-gated current was not the reversal of the in-gated current; moreover, the stoichiometry between GABA and co-ions was not always fixed. Each mode of function required a different set of ions on the two sides of the membrane. We made rapid solution changes and observed an allosteric effect of Na+ that only occurred at the extracellular surface. Thus, the GAT-1 transporter does not behave like a recirculating carrier but may be described as a pore with ion gates at either end that are controlled in part by allosteric sites.
Cammack
J N
JN
Department of Pharmacological and Physiological Sciences, University of Chicago, Illinois 60637.
Rakhilin
S V
SV
Schwartz
E A
EA
D000495:Allosteric Site; D000818:Animals; D001483:Base Sequence; D001692:Biological Transport; D002352:Carrier Proteins / Q000235:genetics / Q000502:physiology*; D002460:Cell Line; D004553:Electric Conductivity; D050485:GABA Plasma Membrane Transport Proteins; D015640:Ion Channel Gating / Q000187:drug effects; D007473:Ion Channels / Q000502:physiology; D008564:Membrane Potentials / Q000502:physiology; D008565:Membrane Proteins / Q000235:genetics / Q000502:physiology*; D026901:Membrane Transport Proteins; D008969:Molecular Sequence Data; D027361:Organic Anion Transporters; D051381:Rats; D012964:Sodium / Q000494:pharmacology; D013816:Thermodynamics; D014162:Transfection; D005680:gamma-Aminobutyric Acid / Q000378:metabolism / Q000494:pharmacology
D002352:Carrier Proteins; D050485:GABA Plasma Membrane Transport Proteins; D007473:Ion Channels; D008565:Membrane Proteins; D026901:Membrane Transport Proteins; D027361:Organic Anion Transporters; C493415:Slc6a1 protein, rat; D005680:gamma-Aminobutyric Acid; D012964:Sodium