Chloride dependence of the K+-stimulated release of taurine from synaptosomes

Exposure of a crude synaptosomal fraction to K⁺ concentrations ranging from 25 to 100 mM evokes the release of [³H]taurine and [³H]GABA. These high concentrations of K⁺ induce, besides depolarization, a marked synaptosomal swelling, which is prevented by replacing chloride in the solutions with the largely impermeant anion gluconate. The depolarizing effect of K⁺ is unaffected by omission of chloride. The K⁺-evoked release of taurine seems related to K⁺-induced changes in synaptosomal volume rather than to a depolarizing effect, since it is totally calcium-independent but is abolished by reducing chloride and by making solutions hypertonic with mannitol. The release of [³H]GABA, in contrast is unaffected in chloride-free or hypertonic solutions.     

Transmitter release in hippocampal slices from rats with limbic seizures produced by systemic administration of kainic acid

The systemic injection of kainic acid (KA) has been shown to destroy neurons in the hippocampus and to induce limbic-type seizure activity. However, little is known on the neurochemical events that are associated with this convulsant effect. In the present work we studied the spontaneous and the K⁺-stimulated release of labeled -aminobutyric acid (GABA), glutamate, serotonin and dopamine, in hippocampal slices of KA-treated rats, at the moment of clinical seizures (2 h) and 72 h later. At the onset of convulsions we found a 40–45% decrease in the K⁺-stimulated release of GABA. The release of the other neurotransmitters was not significantly affected by KA treatment. After 72 h GABA release was still reduced by 30–40%. It is concluded that the epileptogenic effect of KA in the hippocampus is probably related to a diminished inhibitory GABAergic neurotransmission.     

Ischemic flow threshold for striatal dopamine release in rats

To determine the level of cerebral blood flow reduction which causes striatal dopamine release, extracellular dopamine and cerebral blood flow was simultaneously determined using in vivo brain dialysis and a hydrogen clearance method, respectively, in the striatum of spontaneously hypertensive rats, before and during experimental cerebral ischemia. The ischemic flow threshold for neurotransmitter dopamine release was found to be 20% of the resting value or 8–10 ml/100g/min of cerebral blood flow, being similar to those for energy and membrane failures.     

Non-everted oxygenated rat intestinal segments as a measure of neutral detergent fiber effects on iron absorption

Iron absorption in the presence of varying amounts and sizes of dietary fiber was measured. A method using non-everted rat intestinal segments perfused in oxygen was refined. Neutral detergent fiber (NDF), a component of dietary fiber, was extracted from cooked pinto bean (Phaseolus vulgaris). The NDF did not affect iron absorption in intestinal segments from iron replete rats. However, 4 and 6 mg of NDF/ml significantly decreased iron absorption in the intestinal segments from anemic rats. NDF with a smaller particle size of 0.125 mm increased iron absorption relative to that absorbed with 0.180 mm particles. Histological examination validated using non-everted intestinal segments perfused with oxygen as a method for studying dietary effects on iron absorption. Segments which are not everted are less prone to damage. Perfusion with oxygen maintained metabolic activity in the tissue during the experiment.     

Presynaptic regulation of dopaminergic transmission in the striatum

1. In vitro studies have indicated that several transmitters present in the striatum can regulate presynaptically the release of dopamine (DA) from nerve terminals of the nigrostriatal DA neurons. 2. The receptors involved in these local regulatory processes are located or not located on DA nerve terminals. 3. Recent in vivo investigations have demonstrated that the corticostriatal glutamatergic neurons facilitate presynaptically the release of DA and have allowed the analysis of the respective roles of presynaptic events and nerve activity in the control of DA transmission.     

Chromosomes and their relationship to nuclear components during the cell cycle in Chinese hamster cells

Summary Chromosomes and their relationship to nuclear components during various phases of the cell cycle were studied with different fixation, embedding, and enzyme techniques. The results showed that interphase chromosomes may have oriented in such a way that a given locus became associated with the nuclear membrane. Some chromosomes also appeared to interact with the nucleolus. The nuclear matrix materials, however, were distributed between the chromosomes and formed a delineating boundary for the chromosomes. These matrix materials, furthermore, formed channel-like structures within the nucleus and towards the cytoplasm through their interaction with nuclear pore complexes. During mitosis, chromosomes were encapsulated with material that appeared to be derived from the matrix, disintegrated residues and fragments of the nuclear envelope, the lamina, and nucleolar material. These chromosome-associated materials seen in mitosis appeared to serve as foci for formation of new nuclear components in subsequent interphase.     

Role of cell-cycle in regulating neuroepithelial cell shape during bending of the chick neural plate

Summary Neuroepithelial cells transform from spindle-shaped to wedge-shaped within the median and paired dorsolateral hinge points of the bending neural plate, but the mechanisms underlying these localized changes are unclear. This study was designed to evaluate further the hypothesis that localized wedging of neuroepithelial cells during bending involves basal cellular expansion resulting from alteration of the cell-cycle. Neurulating chick embryos were treated with tritiated thymidine, and transverse sections through the midbrain were examined autoradiographically. Parameters of the cell-cycle as well as nuclear position and size were assessed in the median hinge point, which contains predominantly wedge-shaped cells, and in adjacent lateral areas of the neural plate, which contain predominantly spindle-shaped cells. Both the DNA-synthetic phase and non-DNA synthetic portion of the cell-cycle were significantly longer in the median hinge point than in lateral neuroepithelial areas, some nuclei in both regions were located basally during these phases, and virtually all basal nuclei in the median hinge point were large. Additionally, the mitotic phase was significantly shorter in the median hinge point than in lateral areas. We present a model to explain how alteration of the cell-cycle in the median hinge point could generate wedging of cells in this region.     

The arthropod gap junction and pseudo-gap junction: Isolation and preliminary biochemical analysis

Summary The hepatopancreas of the crayfish, Procambarus clarkii, contains an unusual abundance of gap junctions, suggesting that this tissue might provide an ideal source from which to isolate the arthropod-type of gap junction. A membrane fraction obtained by subcellular fractionation of this organ contained smooth septate junctions, zonulae adhaerentes, gap junctions and pentalaminar membrane structures (pseudo-gap junctions) as determined by electron microscopy. A further enrichment of plasma membranes and gap junctions was achieved by the use of linear sucrose gradients and extraction with 5 mM NaOH. The enrichment of gap junctions correlated with the enrichment of a 31 Kd protein band on polyacrylamide gels. Extraction with 20 mM NaOH or 0.5% (w/v) Sarkosyl NL97 resulted in the disruption and/or solubilization of gap junctions. Negative staining revealed a uniform population of 9.6 nm diameter subunits within the gap junctions with an apparent sixfold symmetry. Using antisera to the major gap junctional protein of rat liver (32 Kd) and to the lens membrane protein (MP 26), we failed to detect any homologous antigenic components in the arthropod material by immunoblotting-enriched gap junction fractions or by immunofluorescence on tissue sections. The enrichment of another membrane structure (pseudo-gap junctions), closely resembling a gap junction, correlated with the enrichment of two protein bands, 17 and 16Kd, on polyacrylamide gels. These structures appeared to have originated from intracellular myelin-like figures in phagolysosomal structures. They could be distinguished from gap junctions on the basis of their thickness, detergent-alkali insolubility, and lack of association with other plasma membrane structures, such as the septate junction. Pseudo-gap junctions may be related to a class of pentalaminar contacts among membranes involved in intracellular fusion in many eukaryotic cell types. We conclude that pseudo-gap junctions and gap junctions are different cellular structures, and that gap junctions from this arthropod tissue are uniquely different from mammalian gap junctions of rat liver in their detergentalkali solubility, equilibrium density on sucrose gradients, and protein content (antigenic properties).     

Localized insertion of new S-layer during growth of Bacillus stearothermophilus strains

Bacillus stearothermophilus strains PV 72 and ATCC 12980 carry a crystalline surface layer (S-layer) with hexagonal (p6) and oblique (p2) symmetry, respectively. Sites of insertions of new subunits into the regular lattice during cell growth have been determined by the indirect fluorescent antibody technique and the protein A/colloidal gold technique.During S-layer growth on both bacillus strains the following common features were noted: 1. shedding of intact S-layer or turnover of individual subunits was not seen; 2. new S-layer was deposited in helically-arranged bands over the cylindrical surface of the cell at a pitch angle related to the orientation of the lattice vectors of the crystalline array; 3. little or no S-layer was inserted into pre-existing S-layer at the poles, and 4. septal regions and, subsequently, newly formed cell poles were covered with new S-layer protein.     

Flow cytometric screening and isolation of Escherichia coli clones which express surface antigens of the oil-degrading microorganism Acinetobacter calcoaceticus RAG-1

Flow cytometry (FCM) in conjunction with immunocytochemical-labeling was used to analyze and screen a population of Escherichia coli clones containing a genomic library from the oil-degrading microorganism Acinetobacter calcoaceticus RAG-1 for the isolation of clones which expressed specific RAG-1 surface antigens. Reconstruction experiments using mixed populations indicated that RAG-1 cells could be clearly distinguished at a ratio of one RAG-1 cell to 500 Escherichia coli cells. Using this technique two clones, WM143 and WM191, were isolated and shown by restriction endonuclease cleavage and Southern hybridization to contain plasmids carrying inserts of RAG-1 DNA of 9.4 and 9.8 kb respectively.Non-common abbreviations FCM flow cytometry - FITC fluorescein-iso-thiocyanate - LB Luria broth - MM minimal salt medium - PBS phosphate buffered saline - PMSF phenylmethylsulfonyl fluoride