Characterization of Na +-dependent l-glutamate transport in canine erythrocytes

Abstract

Characteristics of the high-affinity Na +-dependent l-glutamate transport system in canine erythrocytes were studied by using intact cells and resealed ghosts. The l-glutamate transport showed a precise dependence on extracellular Na + and intracellular K +. Kinetical analysis revealed that two Na + ions and one K + ion were involved in each l-glutamate transport cycle. The l-glutamate transport was inhibited most potently by threo-3-hydroxyaspartate and l-cysteinesulfinate (at 25 μM, 83% and 79% inhibition, respectively) and weakly by dihydrokainate and dl-α-aminoadipate (at 25 μM, 21% and 17% inhibition, respectively). From these stoichiometrical and pharmacological properties we concluded that the l-glutamate transport system in canine erythrocytes is a product of the l-glutamate transporter gene family and resembles a neuronal transporter rather than a glial one. l-Glutamate uptake was increased by internal, but not external, HCO 3 − when the internal and external anions of the erythrocytes were replaced by several other anions. Moreover, this enhancement was blocked by inhibition of carbonic anhydrase, which indicated that l-glutamate transport was at least partly dependent on HCO 3 − generated inside the cells. These observations indicate that anion countertransport is coupled to the high-affinity Na +- and K +-dependent l-glutamate transport in canine erythrocytes.