REEVALUATION OF GABA TRANSPORT IN NEURONAL AND GLIAL-CELL CULTURES - CORRELATION OF PHARMACOLOGY AND MESSENGER-RNA LOCALIZATION

Molecular cloning has revealed the existence of four distinct transpor ters for the inhibitory neurotransmitter gamma-aminobutyric acid (GABA ), termed GAT-1, GAT-2, GAT-3, and BGT-1. To determine which of the cl oned transporters are in neurons and which are in glia, we have undert aken a combined pharmacological and molecular biological study using c ell cultures derived from rat brain. In neuronal cultures approximatel y 70% of GABA transport is sensitive to the GAT-1-selective ligand NNC -711 and drug potencies at this site correlate well with their potenci es at GAT-1; GAT-1 mRNA is abundant in these cultures as determined by northern blot analysis. Drug potencies at the NNC-711-resistant compo nent correlate well with their potencies at GAT-2 and GAT-3, whose pha rmacological profiles are similar to one another. Northern blots revea l the presence of mRNA for GAT-3 in neuronal cultures, whereas GAT-2 a nd BGT-1 mRNAs are not detected. Type 1 astrocyte cultures exhibit ver y low levels of GABA transport activity, which has very low potency fo r GABA but high potency for taurine. Such cultures have mRNA for a tau rine transporter and BGT-1, but not for GAT-1, GAT-2, and GAT-3. In cu ltures containing O-2A progenitor cells and Type 2 astrocytes, approxi mately 75% of GABA uptake is sensitive to NNC-711 and drug potencies a t this site correlate well with their potencies at GAT-1; GAT-1 mRNA i s abundant. Drug potencies at the NNC-711-resistant component correlat e well with their potencies at GAT-2 and GAT-3; mRNAs for both of thes e transporters are present (though GAT-2 mRNA is the more abundant), a s is BGT-1 mRNA. In summary, these data demonstrate heterogeneity of b oth neuronal and glial GABA transport.