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P Kontro

Publications and source records attributed to P Kontro.

70 records · Page 4Linked to original sources
PubMed1982

Effects of cations on taurine, hypotaurine, and GABA uptake in mouse brain slices.

The effects of cations on taurine, hypotaurine and GABA uptake were studied in mouse brain slices under identical experimental conditions. The uptakes were all strictly sodium-dependent. The omission or excess of K+ inhibited similarly taurine, hypotaurine and GABA uptake. The effects of omission of Ca2+ or Mg2+ were less pronounced. In both normal-sodium and low-sodium media all uptakes were saturable, consisting of both low- and high-affinity transport components. The Km constants for both low- and high-affinity transport components of hypotaurine and GABA increased in low-sodium medium, suggesting that sodium ions are necessary for their attachment to possible carrier sites in plasma membranes. In the case of taurine, however, the translation rate rather than the affinity of carrier sites was affected in Na+-free media. More than two sodium ions may be involved in the transport of one hypotaurine and one GABA molecule, whereas the coupling ratio between sodium and taurine was at least three. In its cation dependence hypotaurine uptake thus resembled more GABA uptake than taurine uptake.

Animals↗
PubMed1981

Oxidation of hypotaurine in vitro by mouse liver and brain tissues.

The oxidation of hypotaurine to taurine, a reaction so far very poorly characterized in mammals, exhibited characteristic properties of an enzyme-catalyzed reaction in the mouse liver and brain. It was pH- and temperature-dependent and obeyed Michaelis-Menten kinetics when assayed with tissue homogenates using [35S]hypotaurine as substrate. Most of the oxidation activity was recovered in the brain in the soluble fraction whereas in the liver the activity was more evenly distributed among the subcellular fractions. The oxidation was more susceptible to heavy metals and alkylating agents in the brain than in the liver. The activity was higher in both organs in developing than in adult mice. The optimum incubation conditions for oxidation by liver homogenates included pH 9.0, oxygenation of the reaction mixture and the presence of 50 mumol/l Cu2+ and 50 mmol/l NAD+. The specificity of the enzyme(s) for hypotaurine still remains open.

Aging↗
PubMed1981

Hypotaurine transport in brain slices: comparison with taurine and GABA.

Hypotaurine uptake was compared to taurine and GABA uptakes in brain slices under identical experimental conditions. The slices effectively concentrated both hypotaurine and GABA from the medium, whereas taurine was taken up more slowly. The uptakes of these three structurally related amino acids were all saturable, consisting of one low- and one high-affinity transport component. The kinetic parameters of hypotaurine uptake were of the same order of magnitude as those of GABA uptake. All uptake systems were sensitive to temperature, metabolic poisons, and sodium omission. Hypotaurine uptake was inhibited by GABA, L-2,4-diaminobutyric acid (L-DABA), cysteic acid, and beta-alanine, but not by taurine. Taurine uptake was strongly reduced by hypotaurine, beta-alanine, and L-DABA, as well as by GABA, whereas GABA uptake was affected only by cystamine, L-DABA, and nipecotic acid. The uptake processes of hypotaurine, taurine, and GABA were thus fairly similar and showed properties characteristic for neurotransmitter uptake. Hypotaurine uptake resembled more GABA than taurine uptake. The present inhibition studies suggest that there may exist only one common two-component transport system for these three amino acids.

Animals↗
PubMed1981

Cation dependence of hypotaurine uptake in mouse brain slices.

Mouse brain slices take up hypotaurine (2-aminoethanesulphinic acid) from medium by means of two concentrative low- and high-affinity transport systems. [35S]Hypotaurine uptake by the slices was significantly reduced in the absence of external potassium, calcium, or magnesium ions. An excess of potassium ions also inhibited hypotaurine uptake by one-half. Uptake was almost completely abolished on removal of sodium ions. The Km constants for both low- and high-affinity transport components increased in a low-sodium medium, suggesting that sodium ions are required when hypotaurine is attached to its possible carrier sites in plasma membranes. Sodium ions also mimicked allosteric effectors of hypotaurine transport, showing positive cooperativity. More than two sodium ions may be involved in the transport of one hypotaurine molecule across the cell membrane. The calculated activation energies of transport were fairly similar in normal and sodium-deficient media and thus sodium ions may not participate in the activation mechanisms of the transport. With respect to cation dependence, hypotaurine transport in brain slices exhibits features characteristic of neurotransmitter amino acids.

Animals↗
PubMed1980

Free amino acids in the synaptosome and synaptic vesicle fractions of different bovine brain areas.

Free amino acids were quantitatively estimated in intact tissues and isolated synaptosome and synaptic vesicle fractions of the bovine brain regions with the aid of a sensitive amino acid analyzer. The brain areas studied were frontal, parietal and occipital cerebral cortices, cerebellar cortex, caudate and lenticular nuclei, superior colliculi, thalamus, pons and medulla. The most abundant amino acid in tissue samples and synaptosome fractions was glutamic acid, followed by glutamine, aspartic acid, GABA and taurine. The dominatating amino acid in all isolated synaptic vesicle fractions was taurine. The concentrations of glutamic acid, glutamine, GABA and aspartic acid were generally much lower. The 5 transmitter candidates, viz. GABA, glycine, glutamic acid, as particaid and taurine, comprised about one-half of the total amino acids in all samples. Taurine was the only amino acid highly enriched in the vesicle fractions. This enrichment was discernible in all brain areas. It is suggested therefore that taurine is rather a ubiquitous associate of synaptic membrane structures than a specific inhibitory transmitter.

Amino Acids↗
PubMed1980

Hypotaurine uptake by brain slices from adult and 8-day-old mice.

Uptake of [35S]hypotaurine by brain slices prepared from adult and 8-day-old mice was studied at varying temperatures, under O2 and N2 atmospheres, and in the presence of metabolic inhibitors and varying concentrations of hypotaurine in the incubation medium. The tissue/medium concentration gradients generated were exceptionally high for an amino acid. Hypotaurine uptake was energy- and temperature-dependent, more strictly in adult mice. Uptake was saturable, containing a high-affinity and a low-affinity component. The estimated transport constants for the high-affinity uptake of hypotaurine (8-day-old mice, 17.2 mumol/liter; adults, 35.3 mumol/liter) were of the same order of magnitude as the reported transport constants of putative amino acid transmitters, but the total transport capacity appears to be greatest for hypotaurine.

Aging↗
PubMedDate not supplied

GABA, hypotaurine and taurine transport in brain slices from developing mouse.

The kinetics and sodium-dependence of gamma-aminobutyric acid (GABA), hypotaurine and taurine uptake were analyzed in cerebral slices prepared from mice of different postnatal ages. The maximal velocities of transport (V) and the Km constants for the high-affinity uptake all decreased with age, whereas the developmental changes in the low-affinity uptake were exactly opposite. Both high- and low-affinity uptakes were sodium-dependent in all age groups. The general patterns of developmental changes were similar with all three amino acids, in keeping with the assumption of a common transport system for all of them.

Age Factors↗