Effect of the α subunit subtype on the macroscopic kinetic properties of recombinant GABAA receptors

The GABAA receptors (GABARs) are chloride-permeable ligand-gated ion channels responsible for fast inhibitory neurotransmission. These receptors are structurally heterogeneous, and in mammals can be formed from a combination of sixteen different subunit subtypes. Much of this variety comes from the six different α subunit subtypes. All neuronal GABARs contain an α subunit, and the identity of the α subtype affects the pharmacological properties of the receptors. The expression of each of the different α subtypes is regulated developmentally and regionally and changes with both normal physiological processes such development and synaptic plasticity, and pathological conditions such as epilepsy. In order to understand the functional significance of this structural heterogeneity, we examined the effect of the α subtype on the receptor's response to GABA. Each of the six α subtypes was transiently co-expressed with the β3 and γ2L subunits in mammalian cells. The sensitivity to GABA was measured with whole-cell recordings. We also determined the activation, deactivation, desensitization, and recovery kinetics for the six isoforms using rapid application recordings from excised macropatches. We found unique characteristics associated with each α subunit subtype. These properties would be expected to influence the post-synaptic response to GABA, creating functional diversity among neurons expressing different α subunits.