ISOLATION AND CHARACTERIZATION OF A SODIUM- AND CHLORIDE-DEPENDENT GABA TRANSPORTER CDNA FROM TORPEDO CALIFORNICA (SODIUM DEPENDENT)

A Na{dollar}sp{lcub}+{rcub}{dollar}- and Cl{dollar}sp{lcub}-{rcub}{dollar}-dependent GABA transporter, TGAT-1, was cloned from the electric lobe of Torpedo californica using a PCR-based strategy. This investigation developed in the context of a project whose goal was to clone the cDNA for the Na{dollar}sp{lcub}+{rcub}{dollar}- and Cl{dollar}sp{lcub}-{rcub}{dollar}-dependent high affinity choline transporter. Because of the expected abundance of mRNA for this transporter in Torpedo electric lobe neurons, cloning efforts focused on this tissue. However, instead of isolating a choline transporter cDNA a GABA transporter with several interesting features was discovered. First, the nucleotide sequence of TGAT-1 predicts a protein that shows strong sequence preservation with human and rat GAT-1 GABA transporter clones. This may be useful for future studies of functionally important domains of these proteins. Second, this clone appears to be present in non-neuronal cells in the electric lobe, despite the fact that the fish GAT-1 clone encodes a protein with a pharmacology similar to that of mammalian "neuronal" GABA transporters. Preliminary radioligand binding experiments also suggest the presence of multiple components of a GABAergic system in the electric lobe. These results have implications both for the cellular physiology and evolution of Na{dollar}sp{lcub}+{rcub}{dollar}- and Cl{dollar}sp{lcub}-{rcub}{dollar}-dependent transporters.