Sodium dependence of taurine uptake in rat brain synaptosomes

Taurine uptake by synaptosomes isolated from rat brain is strongly inhibited in the absence of sodium ions, in particular within a low concentration range of taurine. Omission of calcium or potassium ions reduces the uptake only slightly. The saturable, high-affinity uptake of taurine is shown to be strictly sodium-dependent, while the low-affinity uptake is only partially sodium-dependent.Sodium ions mimic the actions of allosteric effectors of taurine uptake, showing positive co-operativity. At least three sodium ions may be needed for the transport of one taurine molecule.     

Ultrastructure of synaptosomes from fetal rat brain

The crude mitochondrial fraction P₂ and subfractions of P₂ were prepared from the brain stem, hemispheres and whole brain of 19-day-old fetal rats. Samples were fixed in glutaraldehyde-osmium, NaMnO₄ or by Tranzer's triple fixation method (aldehyde-chromate-dichromate-osmium) and examined by electron microscopy. The C-fraction from whole brain was the main synaptosome fraction, containing 3.2 % presynaptic terminals as counted from all membrane bound particles. The brain stem showed more presynaptic terminals than the hemisphere (2.8% versus 0.9%) suggesting a caudal-rostral maturation gradient for synaptogenesis. The maturity of the nerve endings obtained was very variable in contrast to the rather uniform synaptosomes derived from adult tissue. They varied from profiles without any substructures to mature synaptosomes displaying asymmetric synaptic junctions. Monoamine synaptosomes containing small granular vesicles were not detected in the present study, suggesting immaturity of the granular monoamine pool at this stage of development.     

Volume-activated taurine efflux from the in situ perfused lactating rat mammary gland

The effect of cell swelling on the efflux of amino acids from the in situ perfused lactating rat mammary gland has been examined. Cell swelling, induced by a hyposmotic shock, increased the fractional release of [³H]taurine. In contrast, a hyposmotic shock did not stimulate the efflux of D -[³H]aspartate, suggesting that the effect of a hyposmotic challenge on taurine release cannot be attributed to cell lysis. Volume-activated taurine efflux was reversible, dependent upon the extent of the osmotic challenge and inactivated with a prolonged hyposmotic shock. The release of taurine was also reversibly increased following isosmotic cell swelling (using urea). The results confirm the presence of a volume-sensitive taurine efflux transport system in lactating rat mammary tissue and suggest that the volume-activated amino acid efflux pathway is located at the blood-facing aspect of the mammary epithelium.     

Protein metabolism of rat brain synaptosomes during training

The intensity of metabolism of proteins with fast and slow turnover from cerebral cortical synaptosomes of rats trained in defensive movements, pseudotrained, and control animals was studied by determining their specific radioactivity 1 and 3 days, and 1, 3, 6, and 9 weeks after intraventricular injection of lysine-¹⁴C. Three fractions of synaptosomal proteins, differing in the overall values of their half-life (_{5 0}) were found. An increase was found in the specific radioactivity of brain proteins of the trained animals compared with those of the pseudotrained and control rats. Values of _{5 0} were increased for the slowly metabolized fraction of synaptosomal protein fractions from the brain of the trained rats. The role of protein metabolism in brain synapses in the mechanisms of formation of long-term memory is discussed.Department of Physiology, Medico-Biological Faculty, N. I. Pirogov Second Moscow Medical Institute. (Presented by Academician of the Academy of Medical Sciences of the USSR A. D. Ado.) Translated from Byulleten' Éksperimental'noi Biologii i Meditsiny, Vol. 89, No. 3, pp. 259–260, March, 1980.     

Cysteine sulfinate modulated calcium permeability in synaptosomes from rat brain

Cysteine sulfinate (CSA) was shown to increase 45Ca2+ permeability of plasma membrane of synaptosomes isolated from rat brain. The 45Ca2+ enter through a system which has properties different from those of voltage dependent Ca2+ channels or Na+/Ca2+ exchange. The effect of CSA appeared to be mediated by highly specific receptors saturable by ligand. The high concentrations of CSA required (mM) suggest this amino acid is not the physiological agonist for the receptors.     

Cytosolic free calcium levels increase with age in rat brain synaptosomes

Calcium homeostasis in synaptosomes is altered during ageing. The cytosolic free calcium concentration, [Ca2+]i was determined in synaptosomes and crude synaptosomal fractions from 3- and 24-month-old rats with the fluorescent indicator quin-2. The [Ca2+]i were around two times higher in 24-month-old rats than in adults, both under resting conditions and after K depolarization. This difference was still observed after incubation with an endogenous heavy metal chelator. To avoid the calcium buffering effect of quin-2, [Ca2+]i values were determined with the use of a null-point method and with fura-2. These methods confirmed the increase in [Ca2+]i with age in synaptosomes. The increase in [Ca2+]i in nerve endings may be pathologically important in brain ageing.     

Characteristics of brain injury-derived neurotrophic peptide-binding sites on rat brain synaptosomes and neurons in culture

Brain injury-derived neurotrophic peptide is the fragmental 13-mer peptide of the novel neurotrophic factor which was extracted and purified from Sponge Gelform made of gelatin implanted at the mechanically-induced injury site in neonatal rat brains. Brain injury-derived neurotrophic peptide supports survival of septal cholinergic and mesencephalic dopaminergic neurons in culture, and rescues hippocampal neurons in culture from glutamate neurotoxicity. Here we studied the binding characteristics of brain injury-derived neurotrophic peptide to synaptosomes from normal adult rat brains and neurons in culture from neonatal rat brains. [125I]Asp-[Tyr11]-brain injury-derived neurotrophic peptide binding to rat brain synaptosomes was specific and saturable. Equilibrium binding studies revealed that [125I]Asp-[Tyr11]-brain injury-derived neurotrophic peptide bound to 1.1 pmol/mg protein with a Kd (dissociation constant) of 0.17 microM in hippocampal synaptosomes and to 2.0 pmol/mg protein with a Kd of 0.38 microM in septal synaptosomes. [125I]Asp-[Tyr11]-brain injury-derived neurotrophic peptide could bind to a subpopulation of hippocampal neurons in culture from embryonic rat brains. Affinity cross-linking with the carboxyl-reactive cross-linking reagent 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide-HCl and [125I]Asp-[Tyr11]-brain injury-derived neurotrophic peptide produced radiolabeled bands corresponding to 100,000, 50,000 and 40,000 mol. wt molecules on hippocampal neurons in culture. These results suggest that the 13-mer sequence of brain injury-derived neurotrophic peptide plays a crucial role in expressing the neurotrophic properties of the factor.     

Vasopressin-induced taurine efflux from rat pituicytes: a potential negative feedback for hormone secretion

Previous work on the whole neurohypophysis has shown that hypotonic conditions increase release of taurine from neurohypophysial astrocytes (pituicytes). The present work confirms that taurine is present in cultured pituicytes, and that its specific release increases in response to a hypotonic shock. We next show that vasopressin (VP) and oxytocin (OT) also specifically release taurine from pituicytes. With an EC₅₀ of ∼2 n m , VP is much more potent than OT, and the effects of both hormones are blocked by SR 49059, a V_1a receptor antagonist. This pharmacological profile matches the one for VP- and OT-evoked calcium signals in pituicytes, consistent with the fact that VP-induced taurine efflux is blocked by BAPTA-AM. However, BAPTA-AM also blocks the taurine efflux induced by a 270 mosmol l⁻¹ challenge, which per se does not evoke any calcium signal, suggesting a permissive role for calcium in this case. Nevertheless, the fact that structurally unrelated calcium-mobilizing agents and ionomycin are able to induce taurine efflux suggests that calcium may also play a signalling role in this event. It is widely accepted that in hypotonic conditions taurine exits cells through anionic channels. Antagonism by the chloride channel inhibitors 4,4'-diisothiocyanatostilbene-2,2'-disulphonic acid (DIDS) and 5-nitro-2-(3-phenylpropylamino)-benzoic acid (NPPB) suggests the same pathway for VP-induced taurine efflux, which is also blocked in hypertonic conditions (330 mosmol l⁻¹). Moreover, it is likely that the osmosensitivity of the taurine channel is up-regulated by calcium. These results, together with our in situ experiments showing stimulation of taurine release by endogenous VP, strengthen the concept of a glial control of neurohormone output.     

牛磺酸对弥漫性脑创伤大鼠脑葡萄糖转运体表达的影响

目的: 检测弥漫性脑创伤(DBI)大鼠脑内葡萄糖转运体1(GLUT1)和葡萄糖转运体3(GLUT3)的表达以及牛磺酸对其的影响。方法: SD雄性大鼠随机分为假手术组、脑创伤组、低剂量牛磺酸组(200 mg/kg)和高剂量牛磺酸组(300 mg/kg),连续灌胃给药7 d。建立大鼠DBI模型,脑创伤后24 h,免疫组化和Western blotting检测脑组织中GLUT1和GIUT3蛋白的表达;透射电镜观察大脑皮层神经元超微结构的变化。结果: 各组脑组织中均可见有GLUT1表达的阳性细胞,其表现为在微血管内皮细胞胞浆或胞膜呈棕黄色。与假手术组相比,脑创伤组大鼠脑GLUT1蛋白表达无显著差异;与脑创伤组相比,低、高剂量牛磺酸组脑GLUT1蛋白表达显著增多(P<0.01);且低剂量牛磺酸组脑GLUT1蛋白表达显著高于高剂量牛磺酸组(P<0.05)。各组仅在第三脑室周围可见GLUT3表达的阳性神经元,阳性细胞胞浆或胞膜呈棕黄色。与假手术组相比,脑创伤组大鼠脑GLUT3蛋白表达显著增多(P<0.01);与脑创伤组相比,低、高剂量牛磺酸组脑GLUT3蛋白表达显著增多(P<0.01);且高剂量牛磺酸组脑GLUT3蛋白表达显著高于低剂量牛磺酸组(P<0.01)。低剂量牛磺酸组大脑皮层神经元病理改变明显减轻。结论: 牛磺酸可对DBI大鼠发挥脑保护作用,其机制可能是上调GLUT1和GLUT3蛋白表达,维持脑组织的能量供给。     

Effect of tetanus toxin on noradrenalin liberation from rat brain synaptosomes

A purified preparation of tetanus toxin (TT) (80–800 MLD/mg protein) was shown to induce liberation of both endogenous and exogenous (labeled with¹⁴C) noradrenalin (NA) from isolated nerve endings (synaptosomes) of the rat brain. Within the range of concentrations studied TT does not inhibit secretion of NA evoked by depolarization of synaptosomes by different methods in vitro.Laboratory of General Pathology of the Nervous System, Institute of General Pathology and Pathological Physiology, Academy of Medical Sciences of the USSR, Moscow. Translated from Byulleten' Éksperimental'noi Biologii i Meditsiny, Vol. 89, No. 2, pp. 148–150, February, 1980.     

Biochemical and morphological changes in rat brain synaptosomes after exposure to normobaric hyperoxia in vivo.

Adult rats were submitted to normobaric hyperoxia for 1 to 24 h, then the brain synaptosomes were isolated and their metabolic and morphologic properties were studied. Hyperoxia lasting 1-2 h significantly increased the content of thiobarbituric acid-reactive material (TBAR) and decreased the level of protein thid groups. During the next 5-8 h of hyperoxia SH groups as well as TBAR content became almost normal, reflecting adaptation of the animals to an elevated oxygen tension. After 24 h of hyperoxia a maximal increase in the TBAR content and parallel fall in protein thiol groups were noted. Simultaneously, significant morphological differences between control synaptosomes and synaptosomes isolated from rats exposed to 24 h oxygenation were observed in electron microscopy. The high-affinity dopamine uptake in hyperoxic synaptosomes was significantly increased in all experimental groups. A specific high sensitivity of the dopamine uptake system in synaptoplasmatic membranes to the free radical modification of the membrane structure is suggested.     

Ultrastructural and functional changes in rat brain synaptosomes during electrical stimulation in vitro

Electrical stimulation of a suspension of rat brain synaptosomes leads to significant Ca⁺⁺-dependent liberation of endogenous noradrenalin and to a Ca⁺⁺-dependent increase in its concentration in the synaptosomes themselves. Cyclic nucleotide phosphodiesterase activity is lowered significantly under these same conditions. No disturbance of synaptosomal ultrastructure is found during stimulation. An increase in the number of electron-dense synaptosomes is observed.Laboratory of General Pathology of the Nervous System, Laboratory of Experimental Pathomorphology and Ultrastructural Characteristics of Pathological Processes, Institute of General Pathology and Pathological Physiology, Academy of Medical Sciences of the USSR, Moscow. (Presented by Academician of the Academy of Medical Sciences of the USSR A. M. Chernukh.) Translated from Byulleten' Éksperimental'noi Biologii i Meditsiny, Vol. 89, No. 2, pp. 143–145, February, 1980.     

Effect of electrical stimulation on the influx and efflux of taurine in brain slices of newborn and adult rats

Summary Brain slices from adult and newborn rats were incubated with [³⁵S]taurine in Krebs-Ringer bicarbonate medium at pH 7.4. In both age groups electrical stimulation increased the oxygen consumption of the slices. The influx of taurine only increased in slices from adult rats. The influx conformed to Michaelis-Menten kinetics. In slices from adult rat V_max increased and apparent K_m remained unchanged during electrical stimulation. Both K_m and V_max were greater in adult than in newborn rats. The efflux of taurine from slices depended on the intracellular concentration of taurine and was not measurably influenced by electrical stimulation.