Upregulation of the GABA_A receptor 4 subunit subtype has been consistently shown in multiple animal models of chronic epilepsy. This isoform is expressed in both thalamus and hippocampus and likely plays a significant role in regulating corticothalamic and hippocampal rhythms. However, little is known about its physiological properties, thus limiting understanding of the role of 4 subtype-containing GABA_A receptors in normal and abnormal physiology. We used rapid GABA application to recombinant GABA_A receptors expressed in HEK293T cells to compare the macroscopic kinetic properties of 432L receptors to those of the more widely distributed 132L receptors. These receptor currents had similar peak current amplitudes and GABA EC₅₀s. However, 432L currents activated more slowly when exposed to submaximal GABA concentrations, had more fast desensitization ( = 15-100 ms), and had less residual current during long GABA applications. In addition, 432L currents deactivated more slowly than 132L currents. Peak currents evoked by repetitive, brief GABA applications were more strongly attenuated for 432L currents than 132L currents. Moreover, the time required to recover from desensitization was prolonged in 432L currents compared to 132L currents. We also found that exposure to prolonged low levels of GABA, similar to those that might be present in the extrasynaptic space, greatly suppressed the response of 432L currents to higher concentrations of GABA, while 132L currents were less affected by extrasynaptic GABA. Taken together, these data suggest that 432L receptors have unique kinetic properties that limit the range of GABA applications to which they can respond maximally. While similar to 132L receptors in their ability to respond to brief and low frequency synaptic inputs, 432L receptors are less efficacious when exposed to prolonged tonic GABA or during repetitive stimulation, as may occur during learning and seizures.