GLIA OF THE CHOLINERGIC ELECTROMOTOR NUCLEUS OF TORPEDO ARE THE SOURCE OF THE CDNA-ENCODING A GAT-1-LIKE GABA TRANSPORTER

A PCR-based strategy was used to clone DNAs encoding Na+- and Cl--depe ndent cotransport proteins using DNA from the cholinergic electromotor nucleus of Torpedo californica. This cloning strategy resulted in the isolation of a cDNA clone that shows strong nucleotide sequence homol ogy to the GABA transporter-1 (GAT-1) types of rat and human brain. Wh en expressed in frog oocytes, this transporter mediates the uptake of GABA. Moreover, physiologically and pharmacologically, the Torpedo pro tein behaves very similarly to the rat and human GAT-1 proteins. Howev er, in contrast to the predominantly neuronal localization of the mamm alian GAT-1 proteins, the mRNA for the fish protein is found almost ex clusively in glial elements of the electromotor nucleus. This unexpect ed discovery of a GABA transporter cDNA in a nucleus that has no previ ously characterized GABAergic innervation raises questions about the r ole of GABA and this transporter in the electromotor system. Several s peculative models for GABA function are proposed.