Locations of amino acids in brain slices from the rat. Tetrodotoxin-sensitive release of amino acids

1. Amino acids, particularly glutamate, gamma-aminobutyrate, aspartate and glycine, were released from rat brain slices on incubation with protoveratrine (especially in a Ca(2+)-deficient medium) or with ouabain or in the absence of glucose. Release was partially or wholly suppressed by tetrodotoxin. 2. Tetrodotoxin did not affect the release of glutamine under various incubation conditions, nor did protoveratrine accelerate it. 3. Protoveratrine caused an increased rate of formation of glutamine in incubated brain slices. 4. Increased K(+) in the incubation medium caused release of gamma-aminobutyrate, the process being partly suppressed by tetrodotoxin. 5. Incubation of brain slices in a glucose-free medium led to increased production of aspartate and to diminished tissue contents of glutamates, glutamine and glycine. 6. Use of tetrodotoxin to suppress the release of amino acids from neurons in slices caused by the joint action of protoveratrine and ouabain (the latter being added to diminish reuptake of amino acids), it was shown that the major pools of glutamate, aspartate, glycine, serine and probably gamma-aminobutyrate are in the neurons. 7. The major pool of glutamine lies not in the neurons but in the glia. 8. The tricarboxylic cycle inhibitors, fluoroacetate and malonate, exerted different effects on amino acid contents in, and on amino acid release from, brain slices incubated in the presence of protoveratrine. Fluoroacetate (3mm) diminished the content of glutamine, increased that of glutamate and gamma-aminobutyrate and did not affect respiration. Malonate (2mm) diminished aspartate and gamma-aminobutyrate content, suppressed respiration and did not affect glutamine content. It is suggested that malonate acts mainly on the neurons, and that fluoroacetate acts mainly on the glia, at the concentrations quoted. 9. Glutamine was more effective than glutamate as a precursor of gamma-aminobutyrate. 10. It is suggested that glutamate released from neurons is partly taken up by glia and converted there into glutamine. This is returned to the neurons where it is hydrolysed and converted into glutamate and gamma-aminobutyrate.     

Rutin improves glutamate uptake and inhibits glutamate excitotoxicity in rat brain slices

Molecular Biology Reports - Rutin is an important flavonoid consumed in the daily diet. It is also known as vitamin P and has been extensively investigated due to its pharmacological properties. On...     

A study of the fluid uptake of rat kidney slices in vitro

Rat renal cortical and medullary tissues show a marked elevation of relative water content when immersed in "physiological solutions" containing sodium and chloride ions, or in equally concentrated solutions of monosaccharides. In contrast to this, no increase in relative water content occurs in isosmotic solutions of three disaccharides studied. It appears to be unlikely that the fluid uptake is a result of intracellular hypertonicity existing either physiologically or pathologically. A more satisfactory alternative hypothesis is that ingress of water accompanies entrance of solutes (ions, monosaccharide molecules) into the tissue cells.     

Studies on the specificity of uptake and release of radiolabelled histamine in rat brain slices

Previously it has been shown that radiolabelled histamine is taken up by brain slices and may subsequently be released by depolarizing stimuli in a calcium-dependent manner, indicating the involvement of neurons in uptake and release of histamine.The present study demonstrates that after incubation of brain slices with low (nM) concentrations of [³H]histamine the amine may be taken up by (and released from) dopaminergic and serotonergic neurons (nerve terminals). Thus 6-hydroxydopamine- and 5,7-dihydroxytryptamine-induced lesions not only reduced the uptake of [³H]dopamine (in striatal slices) and [³H]serotonin (in hippocampal slices), but also, though to a lesser extent, that of [³H]histamine. Immunocytochemical findings revealed that the neurotoxins did not visibly affect histaminergic neurons. Lesioning of noradrenergic neurons appeared not to alter significantly the uptake of [³H]histamine. Further, various drugs acting on either catecholamine-, serotonin- or opioid-receptors and known to cause presynaptic inhibition of the release of [³H]dopamine or [³H]wrotonin from striatal or hippocampal slices also inhibited [³H]histamine release.It is concluded that incubation of brain slices with low concentrations of [³H]histamine does not result in a selective labelling of histaminergic neurons. The possibility that, unlike other monoamines, histamine is not subject to high-affinity uptake by the nerve terminals from which it was released, is discussed.     

d-glucosamine uptake by rat brain synaptosomes

Uptake of d-glucosamine by rat brain synaptosomes occurs via a saturable transport process (K_m 2.1 mM, V 3.0 nmol/mg per min) which was clearly distinguishable from simple diffusion. This transport process is highly sensitive to cytochalasin (K_i = 7 · 10^?5 mM. d-Glucose competitively inhibits d-glucosamine uptake with a K_i value of 8 · 10^?1 mM.     

Dimethylnitramine metabolism in vitro by NZR rat liver slices

The net metabolism of dimethylnitramine (DMNO) was studied in NZR rat liver slices in tissue culture medium (Dulbecco's MEM). In rats, mice and fish, liver is the principal target organ for DMNO carcinogenesis. Destruction of DMNO in vitro with oxygenated medium was linear with amount of tissue (0.3-3.0 g liver), and with substrate concentration (0.14-4.44 mM). Substrate destruction (initially 0.2 mM DMNO) was linear for 60 min (average rate 0.9 +/- 0.1 microgram DMNO/g liver/min) and then slowed to become linear again at about half the initial rate from 90 min to longer than 5 h. In anoxic (N2) conditions DMNO metabolism slowed or stopped completely after 70 min. Metabolism of dimethylnitrosamine (DMN) was studied in the same preparation. DMN destruction rates were initially about 50% higher than DMNO, but were equal at longer incubation times. Simultaneous metabolism of DMNO and DMN by the same tissue slices showed DMNO rates unaltered in the presence of equimolar DMN (0.24 mM), but DMN rates were 20-40% depressed. No evidence was found for the oxidation of DMN to form DMNO, or for reduction of DMNO to DMN.