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Biomedical subjects

J Drejer

Publications and source records attributed to J Drejer.

At least 55 records · Page 3Linked to original sources
PubMed1986

Calcium discriminates two [3H]kainate binding sites with different molecular target sizes in rat cortex.

Binding of [3H]kainate to the kainate subtype of excitatory amino acid receptors revealed two binding sites. The high-affinity site (Kd = 3.5 nM) was sensitive to calcium ions and has a molecular target size as determined by high-energy radiation inactivation analysis of 76,600 daltons. The low-affinity site (Kd = 65 nM) was insensitive to calcium ions and has a molecular target size similar to the quisqualate-subtype of excitatory amino acid receptors. The change in binding parameters of the two sites with radiation dose strongly suggests that low affinity, calcium-insensitive [3H]kainate binding sites are equivalent to quisqualate sites.

Animals↗
PubMed1986

Differentiation of Cl-/Ca2+-dependent and sodium dependent 3H-glutamate binding to cortical membranes from rat brain by high energy radiation inactivation analysis.

The molecular weights of 3H-L-glutamate binding in the presence of chloride and calcium ions and in the presence of sodium ions were determined by the high energy irradiation technique. The molecular weight of sodium dependent 3H-L-glutamate binding, which has pharmacological specificities similar to the high-affinity uptake system for L-glutamate, was 670,000 daltons. The high-energy radiation inactivation study of chloride and calcium dependent and sodium independent 3H-L-glutamate binding is consonant with the idea that, this binding represent glutamate transport into resealed plasma membrane vesicles.

Animals↗
PubMed1985

Ontogenetic development of glutamate metabolizing enzymes in cultured cerebellar granule cells and in cerebellum in vivo.

The ontogenetic development of the enzymes phosphate activated glutaminase (PAG), glutamate dehydrogenase (GLDH), glutamic-oxaloacetic-transaminase (GOT), glutamine synthetase (GS), and ornithine-delta-aminotransferase (Orn-T) was followed in cerebellum in vivo and in cultured cerebellar granule cells. It was found that PAG, GLDH, and GOT exhibited similar developmental patterns in the cultured neurons compared to cerebellum. PAG showed, however, a more pronounced phosphate activation in the cultured granule cells compared to in vivo. The activity of GS remained low in the cultured neurons compared to the increasing activity of this enzyme found in vivo. On the other hand Orn-T exhibited an increase in its specific activity in the cultured cells as a function of time in culture in contrast to the non-changing activity of this enzyme in vivo. Compared to cerebellum the cultured neurons exhibited higher activities of GLDH, GOT, and Orn-T whereas the activity of PAG was only slightly higher in the cultured cells. The activity of GS in the cultured neurons was only 5-10% of the activity in cerebellum in vivo. It is concluded that cultured cerebellar granule cells represent a reliable model system by which the metabolism and function of glutamatergic neurons can be conveniently studied in a physiologically meaningful way.

Animals↗
PubMed1985

Cellular origin of ischemia-induced glutamate release from brain tissue in vivo and in vitro.

The uptake and release of D-[3H]aspartate (used as a tracer for endogenous glutamate and aspartate) were studied in cultured glutamatergic neurons (cerebellar granule cells) and astrocytes at normal (5 mM) or high (55 mM) potassium and under conditions of hypoglycemia, anoxia or "ischemia" (combined hypoglycemia and anoxia). In glutamatergic neurons it was found that "ischemic" conditions led to a 2.4-fold increase in the potassium-induced release of D-[3H]aspartate as compared to normal conditions. Hypoglycemia or anoxia alone affected the release only marginally. The ischemia-induced induced increase in the evoked D-[3H]aspartate release was shown to be calcium-dependent. In astrocytes no difference was found in the potassium-induced release between the four conditions and the K+-induced release was not calcium-dependent. The uptake of D-[3H]aspartate was found to be stimulated at high potassium in both glutamatergic neurons (98%) and in astrocytes (70%). This stimulation of D-aspartate uptake, however, was significantly reduced under conditions of anoxia or "ischemia" in both cell types. In glutamatergic neurons (but not in astrocytes) hypoglycemia also decreased the potassium stimulation of D-aspartate uptake. In a previous report it was shown, using the microdialysis technique, that during transient cerebral ischemia in vivo the extracellular glutamate content in hippocampus was increased eightfold. In the present paper it is shown that essentially no increase in extracellular glutamate is seen under ischemia when the perfusion is performed using calcium-free, cobalt-containing perfusion media. The results from the in vitro and in vivo experiments indicate that the glutamate accumulated extracellularly under ischemia in vivo originates from transmitter pools in glutamatergic neurons.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1985

Cultured neurons as model systems for biochemical and pharmacological studies on receptors for neurotransmitter amino acids.

By the use of primary cultures of neurons consisting of cerebral cortex interneurons or cerebellar granule cells it is possible to study biochemical and pharmacological aspects of receptors for GABA and glutamate. Cerebellar granule cells have been shown to express both high- and low-affinity GABA receptors. The latter ones develop, however, only when the neurons are treated with GABA or GABA receptor agonists. It is suggested that the high-affinity receptors play a role in the neurotrophic activity of GABA, whereas the low-affinity GABA receptors are involved in the mediation of the inhibitory action of GABA on evoked release of glutamate, which is the neurotransmitter in cerebellar granule cells. Also glutamate receptors have been studied with regard to the 2 types of neurons. Both cerebral cortex neurons (GABAergic) and cerebellar granule cells (glutamatergic) possess glutamate receptors, which mediate an L-glutamate-induced transmitter release. The pharmacological properties of these glutamate receptors are, however, distinctly different for the 2 types of neurons. While cerebral cortex neurons express both quisqualate-, N-methyl-D-aspartate- and kainate-receptors, the cerebellar granule cells have a receptor which is activated only by L-glutamate and L-aspartate.

Animals↗
PubMed1984

Elevation of the extracellular concentrations of glutamate and aspartate in rat hippocampus during transient cerebral ischemia monitored by intracerebral microdialysis.

Rats were implanted with 0.3-mm-diameter dialysis tubing through the hippocampus and subsequently perfused with Ringer's solution at a flow rate of 2 microliter/min. Samples of the perfusate representing the extracellular fluid were collected over 5-min periods and subsequently analyzed for contents of the amino acids glutamate, aspartate, glutamine, taurine, alanine, and serine. Samples were collected before, during, and after a 10-min period of transient complete cerebral ischemia. The extracellular contents of glutamate and aspartate were increased, respectively, eight- and threefold during the ischemic period; the taurine concentration also was increased 2.6-fold. During the same period the extracellular content of glutamine was significantly decreased (to 68% of the control value), whereas the concentrations of alanine and serine did not change significantly during the ischemic period. The concentrations of gamma-aminobutyric acid (GABA) were too low to be measured reliably. It is suggested that the large increase in the content of extracellular glutamate and aspartate in the hippocampus induced by the ischemia may be one of the causal factors in the damage to certain neurons observed after ischemia.

Amino Acids↗
PubMed1984

GABA induces functionally active low-affinity GABA receptors on cultured cerebellar granule cells.

The effect of gamma-aminobutyric acid (GABA) and its agonists muscimol and 4,5,6,7-tetrahydroisoxazolo[5-4-c]pyridin-3-ol (THIP) on the development of GABA receptors on cerebellar granule cells was studied by cultivation of the cells in media containing these substances. It was found that the presence of 50 microM GABA in the culture media led to the induction of low-affinity GABA receptors (KD 546 +/- 117 nM) in addition to the high-affinity receptors (KD 7 +/- 0.5 nM) which were present regardless of the presence of GABA in the culture media. The functional activity of the GABA receptors was tested by investigating the ability of GABA to modulate evoked glutamate release from the cells. It was found that GABA could inhibit evoked glutamate release (ED50 10 +/- 3 microM) only when the cells had been cultured in the presence of 50 microM GABA, 50 microM muscimol, or 150 microM THIP, i.e., under conditions where low-affinity GABA receptors were present on the cells. This inhibitory effect of GABA could be blocked by 120 microM bicuculline and mimicked by 50 microM muscimol or 150 microM THIP whereas 150 microM (-)-baclofen had no effect. It is concluded that GABA acting extracellularly induces formation of low-affinity receptors on cerebellar granule cells and that these receptors are necessary for mediating an inhibitory effect of GABA on evoked glutamate release. The pharmacological properties of these GABA receptors indicate that they belong to the so-called GABAA receptors.

Animals↗
PubMed1984

Ornithine-delta-aminotransferase exhibits different kinetic properties in astrocytes, cerebral cortex interneurons, and cerebellar granule cells in primary culture.

To evaluate a possible role of ornithine-delta-aminotransferase (EC 2.6.1.13; Orn-T) as a rate-limiting enzyme for the synthesis of transmitter glutamate and gamma-aminobutyric acid (GABA), respectively, its activity and kinetic properties were analyzed in cultured astrocytes as well as in neuronal cultures consisting mainly of glutamatergic neurons (cerebellar granule cells) or GABAergic neurons (cerebral cortex interneurons). For comparison the activity and kinetics of Orn-T were also assayed in mouse brain homogenates. The highest activity of Orn-T was found in astrocytes and in cerebral cortical neurons (5.3 +/- 0.5 and 5.3 +/- 0.4 nmol X mg-1 X min-1, respectively) whereas the activities of Orn-T in cerebellar granule cell cultures and in mouse brain were found to be about half of these values (3.1 +/- 0.3 and 2.8 +/- 0.1 nmol X min-1 X mg-1, respectively). From a kinetic study of Orn-T in the different preparations only a relatively low affinity for the enzyme with respect to ornithine was found in cerebellar granule cells, astrocytes, and whole brain [apparent Km values (at 0.5 mM alpha-ketoglutarate): 4.7 +/- 0.9, 4.3 +/- 2.2, and 6.8 +/- 2.2 mM, respectively] whereas the corresponding Km value for Orn-T in cerebral cortex interneurons was found to be significantly lower (apparent Km: 0.8 +/- 0.3 mM). The enzyme was not found to be inhibited by GABA (range 0.1 - 10 mM) in any of the preparations.

Animals↗
PubMed1983

Novel neuron-related regulatory mechanisms for astrocytic glutamate and GABA high affinity uptake.

The effect of conditioned media from cultures of cerebral cortical neurons and cerebellar granule cells on high affinity uptake of glutamate and GABA into cerebellar astrocytes cultured from 7-day-old rats was studied. Granule cell-conditioned media selectively enhanced GABA uptake whereas cerebral cortex neuron-conditioned media selectively enhanced glutamate uptake into these astrocytes. This selectivity was apparently restricted to cerebellar astrocytes since astrocytes cultured from cerebral cortex of 7-day-old rats exhibited a slight increase in both GABA and glutamate uptake after culture in conditioned media from both types of neurons. The results point to as yet unknown regulatory mechanisms for the development of astrocytic uptake of transmitter amino acids which may be dependent upon the regional origin of the astrocytes as well as the surrounding neuronal cell type.

Animals↗
PubMed1983

Ion dependency of uptake and release of GABA and (RS)-nipecotic acid studied in cultured mouse brain cortex neurons.

The influence of sodium ions on GABA uptake into neurons cultured from cerebral cortex was investigated at sodium concentrations ranging from 16 to 151 mM. Sodium did not affect the Km for GABA uptake but the uptake rates as a function of the sodium concentration was sigmoid at all GABA concentrations studied (1-200 microM). Hill plots of these curves exhibited straight lines with slopes of 1.7-2.1, suggesting that the coupling ratio between sodium and GABA is at least 2. (RS)-Nipecotic acid, a GABA analogue, was transported with high affinity (Km 8.0 +/- 2.1 microM) like GABA, but the Vmax for nipecotic acid was lower than found for GABA (0.664 +/- 0.035 versus 0.955 +/- 0.059 nmol X min-1 X mg-1), suggesting a microheterogeneity of the GABA transport sites. Neurons loaded with the respective tritiated compounds exhibited a pronounced K+-stimulated, calcium-dependent release of both GABA and nipecotic acid indicating that these cultured cells have developed functionally active GABA-ergic synapses.

Animals↗
PubMed1983

Characterization of uptake and release processes for D- and L-aspartate in primary cultures of astrocytes and cerebellar granule cells.

The uptake of L- and D-aspartate was studied in astrocytes cultured from prefrontal cortex and in granule cells cultured from cerebellum. A high affinity uptake system for L- and D-aspartate was found in both cell types, and the two stereoisomers exhibited essentially the same Km- and Vmax-values in both astrocytes (L-aspartate: Km 77 microM; Vmax 11.8 nmol X min-1 X mg-1; D-aspartate: Km 83 microM; Vmax 14.0 nmol X min-1 X mg-1) and granule cells (L-aspartate: Km 32 microM; Vmax 2.8 nmol X min-1 X mg-1; D-aspartate: Km 26 microM; Vmax 3.0 nmol X min-1 X mg-1). To investigate whether L-glutamate, L-aspartate and D-aspartate use the same uptake system a detailed kinetic analysis was performed. The uptake kinetics of each one of the three amino acids was studied in the presence of the two other amino acids, and no essential differences between the uptake characteristics of the amino acids were found. In addition to the uptake studies the release of D-aspartate from cerebellar granule cells was investigated and compared with L-glutamate release. A Ca2+-dependent, K+-induced release was found for both amino acids.

Animals↗
PubMed1983

Pyruvate carboxylase activity in primary cultures of astrocytes and neurons.

The activity of the pyruvate carboxylase was determined in brains of newborn and adult mice as well as primary cultures of astrocytes, of cerebral cortex neurons, and of cerebellar granule cells. The activity was found to be 0.25 +/- 0.14, 1.24 +/- 0.07, and 1.75 +/- 0.13 nmol X min -1 X mg -1 protein in, respectively, neonatal brain, adult brain, and astrocytes. Neither of the two types of neurons showed any detectable enzyme activity (i.e., less than 0.05 nmol X min -1 X mg -1). It is therefore concluded that pyruvate carboxylase is an astrocytic enzyme.

Age Factors↗
PubMed1982

Characterization of L-glutamate uptake into and release from astrocytes and neurons cultured from different brain regions.

The uptake of L-glutamate was studied in astrocytes cultured from different brain areas of newborn rats as well as in two different cultures of neurons obtained from mouse brain. Both astrocytes and neurons exhibited high-affinity glutamate uptake with Km values ranging from 34 microM to 82 microM. Vmax values for astrocytes cultured from the different brain regions were: prefrontal cortex: 13.9; occipital cortex: 11.4; neostriatum: 27.3 and cerebellum: 5.8 nmol X min-1 X mg-1 cell protein. For cerebellar granule cells and cerebral cortical neurons the Vmax values were found to be 10.2 and 5.9 nmol X min-1 X mg-1 cell protein, respectively. The effect on L-glutamate uptake in astrocytes cultured from prefrontal cortex and in cultured cerebellar granule cells of a series of compounds structurally related to glutamate was studied, and detailed kinetic analyses of the inhibitory patterns of three potent inhibitors were performed. L-aspartate and L-aspartate-beta-hydroxamate were found to be competitive inhibitors of L-glutamate uptake in both cell types with Ki values for astrocytes of 60 microM and 91 microM, respectively, and for granule cells of 48 microM and 72 microM, respectively. D-aspartate was found to be a mixed-type noncompetitive inhibitor of L-glutamate uptake in astrocytes (Ki: 106 microM), but in granule cells this compound showed simple competitive inhibition with a Ki of 49 microM. Sodium dependency of L-glutamate uptake in both cell types was studied at a series of L-glutamate and Na+ concentrations. It was found that the uptake of glutamate in astrocytes is coupled with one Na+ ion in contrast to two Na+ ions in granule cells. The Km value for sodium was found to be 15 mM in both cell types. It was shown that release of exogenously supplied [3H]-L-glutamate from cerebellar granule cells could be stimulated in a Ca2+-dependent manner by high concentrations (55 mM) of K+. In contrast to this no K+-induced release of glutamate could be demonstrated in cultured astrocytes.

Animals↗
PubMed1977

Prevalence of residual B-cell function in insulin-treated diabetics evaluated by the plasma C-etide response to intravenous glucagon.

In 83 insulin-treated diabetics the influence of the duration of insulin treatment on the prevalence of residual insulin secretion was examined by determining the plasma C-peptide concentration before and after intravenous injection of 1 mg of glucagon. In 64 patients, plasma C-etide concentration was also determined before and after a standard meal. There was a good correlation between the C-peptide response to glucagon and to the meal (r = 0.67; p less than 0.0001) suggesting that the glucagon test will predict the B-cell response during everyday life. The predictive value of a positive glucagon test was 84% and of a negative test 100%. A preserved, but reduced, B-cell function was demonstrable in 36 of 83 patients. Residual B-cell function was most frequent in the patients with the shortest duration of diabetes. The metabolic importance of endogenous insulin was demonstrated by the significantly lower insulin requirement in the patients with residual B-cell function.

Blood Glucose↗