Phylogenetic conservation of 4-aminobutyric acid (GABA) transporter isoforms. Cloning and pharmacological characterization of a GABA/beta-alanine transporter from Torpedo.

A family of structurally related, Na+/Cl(-)-dependent plasma-membrane transporters catalyze the uptake of several neurotransmitters, osmolytes and other metabolites into cells. Four different members of this transporter family have been cloned from mammalian sources which all transport 4-aminobutyric acid (GABA) but differ in their pharmacological profiles and in their tissue distribution. We report on the cloning, sequencing and functional expression of a transporter for GABA and beta-alanine from the electric lobe of Torpedo. According to similarity of amino acid sequence (77% identity), pharmacological properties, and tissue distribution (nervous-system-specific), it appears to be the counterpart of the beta-alanine-sensitive GABA transporter, GAT-B/GAT-3/GAT4, previously cloned from rat and mouse. The identification of another GABA transporter isoform from Torpedo (after the recent characterization of a Torpedo GAT-1 transporter) indicates that GABA-transporter isoforms are phylogenetically ancient and arose before the divergence of vertebrates. Sequence comparison between isofunctional transporters from evolutionarily distant species aids in the identification of amino acid residues that are critical for functional specificity. The expression of transporters for GABA and beta-alanine raises questions regarding the unidentified physiological role of these amino acids in Torpedo electric lobe.

A creatine transporter cDNA from Torpedo illustrates structure/function relationships in the GABA/noradrenaline transporter family.

A family of homologous, Na+/Cl- dependent plasma membrane transporters catalyze the uptake of a number of neurotransmitters and structurally related compounds into cells. Here, we report the cDNA cloning, sequencing and functional characterization of a non-mammalian member of this transporter family. A creatine transporter from the electric ray, Torpedo marmorata, displays 64% amino acid identity with its rabbit counterpart and has a similar substrate affinity and specificity. Sequence similarity generally is lowest in those regions where also the sequences of other members of the family, transporting different substrates, diverge. Only a few amino acids are better conserved between the two creatine transporters than with the other family members and are candidates for a role in conferring substrate specificity.

A Na(+)-dependent creatine transporter in rabbit brain, muscle, heart, and kidney. cDNA cloning and functional expression.

A cDNA has been cloned from rabbit brain that is a new member of the emerging family of Na(+)-dependent plasma membrane transporters for several neurotransmitters and structurally related compounds. Functional expression of this cDNA in COS-7 cells identifies its product as a Na(+)- and Cl(-)-dependent creatine transporter with a Km of approximately 35 microM. Its creatine transporter activity is efficiently antagonized by 3-guanidinopropionate, a well characterized alternative substrate of creatine transport in several tissues, and by 4-guanidinobutyrate. More distant structural analogues of creatine are much less efficient or inactive as antagonists, indicating a high substrate specificity of the transporter. Northern blot hybridization detects the expression of its mRNA in most tissues tested, most prominently in kidney, heart, and muscle, but not in liver and intestine. A full-length cDNA clone was also isolated from a muscle cDNA library and found to contain the same coding sequence. Substrate affinity and specificity of the cloned transporter are very similar to the endogenous creatine transporter of the COS-7 cells and to the creatine transport activities of several cell types described in the literature. Moreover, its mRNA is most abundant in the tissues known to possess high creatine uptake capacity.

Iodobenzamide for in vivo exploration of central dopamine receptors: evaluation in animal models of supersensitivity.

Iodobenzamide is a promising agent to investigate D2 receptors by SPECT in living human brain. In this work, we have evaluated this radiolabeled compound in two animal models of D2 receptors supersensitivity. In the first model, rats were treated chronically with haloperidol during three weeks (S.C. injection of 0.5 mg/kg/day). One week after the last day of treatment, they were I.V. injected with 125I-IBZM. In vivo specific binding study showed a 45 percent increase of 125I-IBZM fixation in the striatum of treated rats. In a second step of experiments, animals were unilaterally lesioned by a stereotaxic injection of 6-OHDA in the substantia nigra, 23 days before receiving 125I-IBZM. Autoradiographic analysis of coronal brain sections showed a 38 percent enhancement of 125I-IBZM in vivo binding in the striatum on the lesioned side as compared to the contralateral intact side; this increase occurred in striatal lateral area. These data demonstrate that 125I-IBZM is convenient to detect alterations of dopamine D2 receptors in vivo in the rat. Thus IBZM labelled with 123I can be a very useful imaging agent for the exploration of D2 receptors in pathological situations.

Iodoethylspiperone, a new potential agent for exploration of central dopamine D2 receptors: synthesis and preliminary in vivo study.

We synthesized a new spiperone derivative: iodoethylspiperone (IES) to perform dopamine D2 receptor exploration by SPECT. IES was prepared from a precursor: tosylethylspiperone, and characterized by i.r. and 1H-NMR analyses. [125I]IES was obtained with 80% yield. In vivo biodistribution in rats showed a high and specific uptake in the striatum. The uptake ratio between the striatum and the cerebellum reached a maximum value 4 h after injection (10.05 +/- 2.81). IES labeled with 123I should be a promising new agent to investigate D2 receptors in the living human brain.

[Research on the psychopharmacologic profile of new barbiturics]. / Recherche du profil psychopharmacologique de nouveaux barbituriques.

The detection of psychopharmacological properties of 8 synthetic substances derived from barbituric didn't allow to consider the existence of well characterised psychotropic properties, particularly hypnotical, but only antalgic and sedative effects (or stimulating activity very low). If the presence of a benzyl substituent can confer an affinity for the nervous central system superior to the one developed when an allyl rest is in the same position, the presence of an OH or OCH3 in other place inverse the sedative character in stimulant potentiality.