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Notes: Abstract: Effects of altered composition of membrane lipids on high-affinity uptake of l-glutamate and taurine were studied in an established neuroblastoma cell line M1. Increase in participation of certain fatty acids (20: 5ω3 and 22: 5ω3) as constituents of membrane lipids resulted in a fourfold increase in the maximum initial rate of l-glutamate uptake (Vmax) while increase in Vmax of taurine uptake was much smaller. Neither structural requirements of l-glutamate uptake nor passive permeability of the membrane to l-glutamate or taurine seemed to be influenced by the alterations in the lipid composition. Since increased proportions of 20: 5ω3 and 22: 5ω3 in the membrane phosphatides caused no dramatic changes in kinetic parameters of taurine uptake and incorporation of either linoleic or linolenic acid alone into the phosphatides had only a relatively small effect on some of the measured parameters, the possibility of a specific relationship between 22: 5ω3 and/or 20: 5ω3 and l-glutamate uptake is discussed. Unlike l-glutamate uptake systems in other preparations, the high-affinity uptake system of l-glutamate in neuroblastoma cells did not readily accept l-aspartate as a substrate.

Notes: Abstract: γ-Hydroxybutyrate (GHB) is a compound with numerous neuropharmacological properties. The discovery of its biosynthetic system, together with its endogenous repartition, have prompted its possible implication in neurotransmission. This role is also supported by the existence, reported here, of a high-affinity uptake system for GHB (Km= 46.4 μM)in both purified brain plasma membrane vesicles and in the crude mitochondrial fraction. GHB uptake is dependent on a Na+ gradient but is independent of the membrane electrical potential. Cl− and K+ can also modulate the uptake. As an approach to determine the conformation required for GHB uptake, a series of related compounds, including aryl-or alkyl-derivatives, has been examined for ability to inhibit GHB uptake. The regional distribution of uptake is also indicative of its possible physiological role, since in striatum, an area where GHB has a known pharmacological effect on dopaminergic neurons, this uptake activity is the highest.

Notes: Abstract: Rat brain contains two major NADPH-linked aldehyde reductases that can reduce succinate semialdehyde to 4-hydroxybutyrate. One of these enzymes appears to be fairly specific for succinate semialdehyde and is not significantly inhibited by classic aldehyde reductase inhibitors such as barbiturates. The other enzyme can reduce several aromatic aldehydes and is strongly inhibited by barbiturates and branched-chain fatty acids. Using one such inhibitor, it was possible to distinguish between and measure the two enzyme activities separately in various rat brain regions and in subcellular fractions. Both enzymes are mainly cytoplasmic but there is some activity in the synaptosomal fraction. The activity of the specific succinic semialdehyde reductase is highest in the cerebellum, where it represents 21% of the total activity, and lowest in the cortex, where it represents about 11% of the total activity.

Notes: The uptake of calcium was examined in primary cultures of pure neurons and of glial cells from dissociated hemispheres of chick embryo brain. Neuronal cultures took up calcium at a rate of 2.0 nmol per min per mg cell protein at medium concentrations of 1.2 mM-Ca2+ and 5.4 mM-K+. The rate of calcium entry into neurons was increased 2.7-fold by elevating medium potassium to 60 MM. The effect of high external potassium was to increase the Vmax value for calcium transport from 5.5 to 13 nmol per min per mg; the Michaelis constant for calcium, 1.2 mM, was unchanged. The potassium-dependent component of calcium entry into the neuronal cultures was eliminated by addition of 0.1 mM-D-600 (a verapamil derivative) or by 1 mM-CoCl2, but 0.5 μM-tet-rodotoxin had no significant effect. When choline replaced potassium in uptake medium no change in calcium transport was detected in neurons, nor was the entry of calcium increased when choline replaced sodium. Glial cultures took up calcium at 20% of the basal rate for neuronal cultures on a weight-of-protein basis. Uptake was not increased by potassium; during depolarization by potassium the calcium transport activity of glia was less than 10% that of neurons. It was concluded that cultured neurons contain a depolarization-sensitive, calcium-specific channel. A similar calcium transport activity was not detected in cultured glial cells.

Notes: Abstract: The influence of the time of culture on GABA and taurine uptake was investigated in spontaneously matured cultures of glial and neuronal origins and in cultures treated with cyclic nucleotides. In the spontaneously matured cultures the capacity of the high-affinity neuronal GABA transport system increased with time in culture. Essentially opposite results were found for the uptake of GABA by glial cultures. In contrast with the neuronal uptake of GABA, the capacity of the taurine transport system was significantly decreased. Uptake of taurine into glia, however, exhibited a progressive increase with the period of culture. The values of Km, for the high-affinity systems were always found to range around 10 μM. It is suggested that, in mature cells, neuronal uptake sites are of prime importance for GABA transport, while taurine uptake may be more specifically directed towards glial cells. When cultures were treated with cyclic nucleotide derivatives, a morphological differentiation was induced, which could not be linked to a stimulation of GABA or taurine uptake systems as compared with the non-treated cultures.

Notes: Abstract: Ethanolamine and choline glycerophospholipids are the major phospholipids of brain membranes. During brain development, the accumulation of these phospholipids is most intense when myelination occurs. In order to gain knowledge about the regulatory mechanisms for synthesis of these lipids in relation to membrane synthesis, we investigated the activities of the 1,2-diradyl-sn-gIycerol: CDPethanolamine phosphoethanolarnine transferase and 1,2-diradyl-sri-glycerol:CDPcholine phosphocholine transferase during chicken brain development. Diacyl, alkenylacyl, and alkylacylglycerols are substrates for both enzymes. The specific activities of microsomal phospho-ethanolamine and phosphocholine transferases are constant between the 8th and 18th day of embryonic life. The specific activities of both enzymes double around hatching, which is the period of intense myelination and marked ac-cumulation of ethanolamine and choline glycerophospholipids in brain. At the same time, the amount of microsomes increases by 50%; thus the total activities increase threefold. Four days after hatching the specific activities of both enzymes are at adult values. Similar results were obtained in the presence of exogenous diacyl or alkylacylglycerols. During brain development the apparent Km, value of rnicrosomal phosphoethanolamine transferase for CDP ethanolamine increases when assayed with diaclyglycerols or alkylacyl-glycerols a s lipid substrates. The apparent Km, value of phosphocholine trans-ferase for CDP choline does not change during brain development in the presence of exogenous diacylglycerols, but increases in the presence of exogenous alkylacylglycerols. These changes in Km, values may be due to the appearance of glial isoenzyme at the beginning of myelination. The apparent Km, values of diacylglycerol phosphocholine, alklyacylglycerol phosphocholine, and diacyl-glycerol phosphoethanolamine transferases for their CDP bases are similar in adult brain microsomes and are threefold higher than the apparent Km, value of alkylacylglycerolphosphoethanolamine transferase. The high affinity of alkylacylglycerolphosphoethanolamine transferase for CDPethanolamine may be responsible for the preferential synthesis of ethanolamine plasmalogens in brain.

Notes: The metabolism of sphingomyelins containing short-chain fatty acids (C18:sphingomyelin) and those containing long-chain fatty acids (C24:sphingomyelin) in microsomes and myelin from rat brain were studied for periods from 1 to 60 days after intracisternal injection of [32P]Na2HPO4. In microsomes the half-lives of both molecular species of sphingomyelin were 14 days. In myelin the half-life of C18:sphingomyelins was 69 days, whereas C24: sphingomyelins exhibit a high degree of metabolic stability. The results suggest that in myelin the sphingomyelins containing short-chain fatty acids may be located in the inner leaflet of the bilayer and those containing long-chain fatty acids may be located in the outer leaflet.