GAT-1, a high-affinity GABA plasma membrane transporter, is localized to neurons and astroglia in the cerebral cortex

Abstract

High affinity, GABA plasma membrane transporters influence the action of GABA, the main inhibitory neurotransmitter. The cellular expression of GAT-1, a prominent GABA transporter, has been investigated in the cerebral cortex of adult rats using in situ hybridization with 35S-labeled RNA probes and immunocytochemistry with affinity purified polyclonal antibodies directed to the C-terminus of rat GAT-1. GAT-1 mRNA was observed in numerous neurons and in some glial cells. Double-labeling experiments were performed to compare the pattern of GAT-1 mRNA containing and GAD67 immunoreactive cells. The majority of neurons expressing GAT-1 mRNA also contained GAD67 immunoreactivity (ir), but GAT-1 mRNA was also observed in a few pyramidal neurons. GAT-1-ir was localized to numerous puncta and fibers and to astrocytic processes, was not observed in sections incubated in GAT-1 antibodies preadsorbed with rat GAT-1 C-terminal peptide, and was observed in sections incubated in GAT-1 antibodies preadsorbed with the C-terminal portion of the related peptides rat GAT-3(607-627) or rat glycine transporter-1(625-633). The highest number of GAT-1-ir puncta was in layer IV, followed by layers II-III. GAT-1 positive puncta appeared to have a preferential relationship to the soma and proximal dendrites of unlabeled pyramidal cells. All GAT-1 positive axon terminals formed symmetric synapses. This study demonstrates that (1) GAT-1 is expressed by both neurons and astrocytes, (2) the majority of GAT-1 expressing neurons contain GAD67, and (3) GAT-1 uptake system is more extensive than the GABA synthetizing system. These observations support the hypothesis that, in addition to its role in terminating GABA action by uptake into GABAergic axon terminals, GAT-1 influences both excitatory and inhibitory transmission by modulating the "paracrine" spread of GABA (Isaacson et al., 1993), and suggest that astrocytes may play an important role in this process.

Expression of GABA transporter subtypes (GAT1, GAT3) in the adult rabbit retina

“…5). There are similar observations in rat brain, and it has been speculated that this presumably postsynaptic transporter assists in removing neurotransmitter GABA from the synaptic cleft (Snow et al 1992;Swan et al 1994;Minelli et al 1995). Our observations suggest that this may be the case also in rabbit retina.…”

Regulatory mechanisms that modulate signalling by G-protein-coupled receptors

“…They are often located on neurons and glial cells, and are thus ideally placed to remove neurotransmitters at sites of release and action (Figure 2a). For example, GAT-1, a high-affinity γ-aminobutyric acid transporter, is expressed at the plasma membrane of numerous axonal terminals of neurons in the central nervous system that also express the γ-aminobutyric acid-synthesizing enzyme glutamate decarboxylase [8].…”

The Role of N-Glycosylation in Transport to the Plasma Membrane and Sorting of the Neuronal Glycine Transporter GLYT2

“…In this sense, various transporters show a differential distribution among membrane domains of the cells where they are expressed. For instance, the GABA transporter, GABA transporter 1, the transporters for biogenic amines, and the glycine transporter GLYT2 are concentrated in presynaptic terminals (17)(18)(19)(20). In non-neural cells, the betaine transporter, a member of the GABA transporter subfamily, is expressed in the basolateral membrane of epithelial MDCK cells (21).…”