Title: Effect of GABA Concentration on Current-Voltage Properties of the GABA(A) Receptor
Abstract: The γ-aminobutyric acid type A (GABAA) receptor functions as a chemical to voltage transducer in the central nervous system, converting neurotransmitter signals to changes in postsynaptic membrane potential. The kinetics of GABAergic currents are known to be affected by membrane potential, but the dependence on neurotransmitter concentration has not been fully explored. The present study investigates the current-voltage (IV) relationship of α1β2γ2s GABAA receptors across a range of GABA concentrations using whole-cell patch clamp of transfected HEK293 cells. We have determined and validated a voltage ramp protocol verses a more traditional stepwise procedure, in order to rapidly quantify rectification, hysteresis and the reversal potential at GABA concentrations ranging from 0.3 to 1000 μM. Results show that the rectification and hysteresis of the IV curves are dependent on GABA concentration, whereas the reversal potential is independent. Specifically, measures of rectification and hysteresis segregated into two distinct populations, at low (0.3-10 μM) and high (30-1000 μM) GABA concentrations. We provide evidence that the current-voltage properties of GABAA receptors are concentration dependent and, consequently, that the GABA concentration must be taken into context when designing experiments and interpreting results. Finally, these results have implications for a better understanding of synaptic responses where receptor location plays a role in the level of GABA exposure.