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Notes: Abstract— (1) Mouse cerebrum slices swell in tris-buffered Krebs-Ringer medium. Swelling is rapid at first, then slows to a more or less constant rate. Even after 3 hr incubation, water content/g of tissue dry wt. shows no sign of an asymptotic limit. Swelling is the same at 37° and at 0°.(2) Tissue water measured by incubation with tritiated water is equal to total tissue water measured by drying slices. Equilibration between tritiated water and tissue water is complete within 2 min.(3) Tissue liquid can be divided into three phenomenologically distinguishable compartments: first inulin space, which is the compartment permeable to inulin at both 0° and 37°; second inulin space, which is the compartment permeable to inulin at 37° but not at 0°; and 37°non-inulin space, which is the compartment impermeable to inulin at both 0° and 37°. The evidence for this is:(a) Penetration of inulin into tissue is greater at 37° than at 0°. After the first 20 min the rate of penetration at 0° is approximately equal to the rate of penetration at 37°, and only slightly less than the rate of increase of total tissue water. Therefore the smaller inulin space observed at 0° cannot be due to slower entry of inulin.(b) The inulin content of slices incubated in inulin-containing medium at 37° and cooled to 0° in the same medium is the same as the inulin content of tissue incubated at 37° without subsequent cooling. In contrast, the inulin content of tissues preincubated in inulin-free medium at 37° and then incubated in inulin-containing medium at 0° is the same as the inulin content of tissues incubated in inulin-containing medium at 0° without preincubation at 37°. Therefore the smaller inulin space at 0° than at 37°can be due neither to a reversible temperature-dependent change in the size of one single inulin space nor to an irreversible, greater swelling of a single inulin space at the higher temperature, but is due to some portion of the 37° inulin space becoming impermeable to inulin at 0°.(c) Some inulin is retained by tissue incubated with inulin at 37°, then transferred to inulin-free medium at 0°; the amount of retained inulin is equal to the difference between inulin content of tissue incubated with inulin at 37° and tissue incubated with inulin at 0°. This confirms 3b above and in addition shows that inulin which has entered the second inulin space at 37° is trapped there when this space becomes impermeable to inulin at 0°.(4) The penetration of the amino acids, L-lysine and D-glutamate at 0° is equal to the penetration of inulin at 37°. This confirms the real existence of the 37° inulin space at 0°, and shows that the barrier at 0° between the first and second inulin spaces does not exist for these substances.(5) The amino acids L-leucine and glycine penetrate total tissue water at 0°. L-leucine is actively transported at this temperature.(6) The amino acids α-aminoisobutyric acid, L-leucine, and L-lysine at 2 mm have no effect at 37° on either the inulin space or the non-inulin space.(7) The inulin space is insensitive at 37° to physiologically significant changes in the medium. In contrast, the non-inulin space is quite sensitive to these changes. Addition of D-glutamate greatly increases the non-inulin space; addition of ouabain or cyanide, or omission of glucose, increases the non-inulin space slightly; and replacement of Na+ ion by choline+ ion greatly decreases this space. These changes are independent and roughly additive.

Notes: : The properties of the uptake of nucleosides and nucleotides by brain cells were examined in slices of mouse brain. Of the compounds tested, adenine and adenosine had the most rapid uptake and reached the highest levels. Uptake was mediated, as shown by saturability and strong inhibition, by low temperature, or by cyanide, and was only partially sodium- or calcium-dependent. The inhibition pattern by analogues indicated the presence of several uptake systems (possibly four), as shown by differences between adenine and guanine uptake, between adenine and adenosine uptake, and between adenosine and cytidine uptake. The properties of uptake systems for nucleotides and nucleosides were somewhat different from those for amino acids.

Notes: Abstract: Thyroid hormones and their derivatives were found to inhibit [3H]flunitrazepam binding stereospe-cifically and in a monophasic manner. Among the compounds tested, D-thyroxine was the most potent inhibitor (IC50= 0.5 μM). The naturally occurring L-thyroxine was about 40-fold less potent (IC50= 20 μM). The structure-activity relationships seem to imply that the thyronine base has the principal role in the inhibition of benzo-diazepine receptor binding. The type of inhibition was examined with the most potent inhibitor, D-thyroxine, by Scatchard analysis. The apparent dissociation constant (KD) of the [3H]flunitrazepam binding increased and the receptor density (Bmax) decreased as a function of D-thyroxine concentration; this is characteristic of mixed-type inhibition.

Notes: —The Na+ requirement of amino acid transport was measured in brain slices. The tissue was first washed free of Na+ and then Na+ was replaced by one of the following: choline, Li+, Rb+, or mannose. Amino acid uptake was measured at different times (5–120 min) and at low (10-7–10-5m) and high (10-3m) concentrations. Most of the Na+ could be washed out of the tissue; this also decreased K+ levels despite increased K+ in the medium. K+ tissue levels were partially restored when Na+ was added.The absence of Na+ abolished the uptake of Glu, Asp, GABA, Gly, Tau and Pro. Most of the neutral amino acids (Ala, Val, Trp, His) were very strongly inhibited by the absence of Na+ under most experimental conditions. Basic amino acids (Arg, Lys) were not completely inhibited, in that 30 per cent of the equilibrium uptake remained and some of the basic amino acid influx was independent of the Na+ tissue level. The uptake of amines (tyramine, cadaverine, putrescine) did not require Na+, and often was greater in the absence of Na+.We conclude that amino acid uptake in brain slices is Na+ dependent, although the absence of Na+ may affect transport indirectly.

Notes: Abstract— Adult mice were fed standard diets that were enriched with selected amino acids, i.e. 3% methionine, 6% valine, or 8% lysine. These diets caused the following changes in the amino acid pool of the brain measured at 7 and 21 days. The high methionine diet resulted in 50-fold higher levels of methionine and cysteine and somewhat lower levels of serine and glutamine. The valine and lysine-enriched diets also caused 2- to 4-fold increases in valine and lysine contents of brain, respectively. In spite of the large changes in amino acid levels, however, there were essentially no changes in aspartate: α-ketoglutarate, alanine: α-ketoglutarate, ornithine: α-ketoglutarate, methionine: α-ketoglutarate, and the branched chain aminotransferase activities of brain 3, 10, and 21 days after the onset of the dietary regimen. In contrast, these diets produced significant changes in some of these enzyme activities in liver. Changes in liver included a 2-fold increase in ornithine and alanine aminotransferase activities with the methionine-enriched diet. Liver ornithine aminotransferase activity also increased slightly in animals fed the valine-enriched or lysine-enriched diet.

Notes: Peptide and peptidyl-peptide hydrolase activities were measured in the cerebral cortex, adenoand neurohypophysis, anterior and posterior regions of the hypothalamus to assess regional differences in peptide hormone turnover. In general all enzyme activities were higher in the pituitary except for the monoacyl arylamidase which was lower, and neutral proteinase which was distributed more evenly in all regions. Of the enzymes measured the highest activities occurred in the presence of the di- and tripeptide substrates (aminopeptidases); this activity was some 20-60-fold higher than the acid and neutral proteinases. Comparison of the peptide-amide substrates revealed the highest activity with the monoacyl derivative which was five-fold higher than the dipeptidyl, and 50-fold higher than the tripeptidyl (hormonal) factor Pro-Leu-Gly. NH2. Analysis of the breakdown products of the hormonal factor indicated inactivation by N-terminal release of Pro, Leu with Gly. NH2 as the final product. Regional differences in enzyme content in neurosecretory areas suggest that this plays a role in the turnover of specific hormones.