The surface density of the glutamate transporter EAAC1 is controlled by interactions with PDZK1 and AP2 adaptor complexes.

The glutamate transporter excitatory amino acid carrier (EAAC1/EAAT3) mediates the absorption of dicarboxylic amino acids in epithelial cells as well as the uptake of glutamate from the synaptic cleft. Its cell-surface density is regulated by interaction with accessory proteins which remain to be identified. We detected a consensus sequence for interaction with post-synaptic density-95/Discs large/Zonula occludens (PDZ) proteins (-SQF) and a tyrosine-based internalization signal (-YVNG-) in the C-terminus of EAAC1, and investigated their role in the transporter localization.

Functional expression of type 1 rat GABA transporter in microinjected Xenopus laevis oocytes.

In this chapter we describe technical aspects and experimental potential of the two electrodes voltage clamp (TEVC) electrophysiological approach applied to the Xenopus oocyte-expression system. This technique is addressed to the study of a particular class of expressed proteins, those responsible to drive ion fluxes through the plasma membrane. In fact the voltage-clamp technique provides the most direct and sensitive measurement of the functional properties of ion channels and electrogenic transporters, allowing specific ion currents to be recorded under well-defined voltage conditions and temporal control.

Oligomeric structure of the neutral amino acid transporters KAAT1 and CAATCH1.

The highly homologous neutral amino acid transporters KAAT1 and CAATCH1, cloned from the midgut epithelium of the Manduca sexta larva, are members of the Na(+)/Cl(-)-dependent transporter family. Recent evidence indicates that transporters of this family form constitutive oligomers. CAATCH1 and KAAT1 give rise to specific kinds of current depending on the transported amino acid, cotransported ion, pH, and membrane voltage.

Baclofen and potential therapeutic use: studies of neuronal survival.

Up to now, baclofen (a GABA(B) receptor agonist) has been used for the treatment of severe spasticity unresponsive to oral antispasmodics. Although in humans it is usually administered at 2 mg/ml, the dosage to be used in the treatment of other diseases is unknown. For this reason, it is important to determine the safe maximum dosage and toxicity at the clinically used concentration.

Relations between substrate affinities and charge equilibration rates in the rat GABA cotransporter GAT1.

The relations between apparent affinity for substrates and operating rates have been investigated by two-electrode voltage clamp in the GABA transporter rGAT1 expressed in Xenopus oocytes. We have measured the transport current induced by the presence of GABA, as well as the charge equilibration rate in the absence of the neurotransmitter, in various experimental conditions known to affect the transporter characteristics. The apparent affinities for GABA and for Na(+) were also determined in the same conditions.

Structural domains involved in substrate selectivity in two neutral amino acid transporters.

The ability of the two highly homologous Na(+)/Cl(-)-dependent neutral amino acid transporters KAAT1 and CAATCH1, cloned from the midgut epithelium of the larva Manduca sexta, to transport different amino acids depends on the cotransported ion, on pH, and on the membrane voltage. Different organic substrates give rise to transport-associated currents with their own characteristics, which are notably distinct between the two proteins. Differences in amplitude, kinetics, and voltage dependence of the transport-associated currents have been observed, as well as different substrate selectivity patterns measured by radioactive amino acid uptake assays.