Mechanisms of heterogeneity of calcium response to kainate and neuronal types in rat cortical primary culture

The dynamics of intracellular Ca²⁺ signal in response to NMDA (N-methyl-D-aspartate, 30 μM) or KA (kainite, 30 μM), its dependence on extracellular Ca²⁺ and the mechanisms of KA-triggered Ca²⁺ entry into neurons have been tested in neurons of rat cortical primary cultures. The level of intracellular free Ca²⁺ concentrations ([Ca²⁺] _i ) was evaluated on Leica SP5 MF confocal microscope using Fluo-3 fluorescent dye, which resolves changes in [Ca²⁺] _i in the micromolar range. The dynamics of [Ca²⁺] _i increase in response to NMDA and KA was different but in both cases the [Ca²⁺] _i increase required the presence of Ca²⁺ in the extracellular solution. The neuronal population was found to be heterogeneous, based on the response to KA applied together with either L-type calcium channel blocker nifedipine (3 μM) or IEM-1460 (3 μM), a blocker of Ca²⁺-permeable AMPAR (α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor) lacking GluR2 subunit. Experiments exhibited three types of calcium responses, characteristically belonging to interneurons (expressing Ca²⁺-permeable AMPAR), pyramidal neurons (with AMPAR containing GluR2, making them impermeable to Ca²⁺), and intermediate type of cells expressing both AMPAR types. Thus, we have demonstrated the role of AMPAR and L-type calcium channels in KA-triggered Ca²⁺ entry into neurons. The dynamics of [Ca²⁺] _i during the KA treatment was shown to depend on subunit composition of particular AMPAR subtype expressed in neurons. The data suggest that neuronal types existing in adult cortical tissue are probably presented in primary culture, too.     

Phosphorylation of proteins in cytoplasmic and nuclear fractions of human cells treated with double-helical RNA and human recombinant interferon type I]

The dynamics of protein kinases activity in nuclear and cytoplasmic fractions of human fibroblasts treated by preparations of natural and synthetic dsRNA (ridostin, rifastin, larifan and poly(I).poly(C), DEAE-dextran and dsRNA complexes with DEAE-dextran), as well as by preparations of recombinant alpha-2 and beta-1 interferons was obtained. The early activation of enzymes in treated cells extracts and their presence in dsRNA-activated and nonactivated forms were found. In cytoplasmic cellular fractions treated by interferons the dsRNA dependent protein kinases (nonactivated forms- were prevalent.r In contrast, in dsRNA treated cells or dsRNA complexes with DEAE-dextran treated ones the dsRNA independent protein kinases (activated forms) were found, while dsRNA dependent forms induced by interferons were found at later periods. Nuclear protein kinases are mainly dsRNA independent making possible the supposition of their intracellular activation by incoming dsRNA or interferon-induced formation of ds-structures in cellular nuclei. In phosphorylated proteins spectre the 90, 69, 45-40 and 30-35 kDa polypeptides were found. At early intervals in nuclear fractions was found a nuclease resistant and partially EDTA resistant high molecular phosphorylated complex (120 kDa). The complex is, probably, capable of dissociation to low mol mass components. DEAE-dextran induces strong activation of protein kinases in cytoplasm and nuclei and increases the content of activated forms of enzyme in larifan treated cells.     

Synthesis of oligosaccharide fragments of the capsular polysaccharide of Streptococcus pneumoniae type 3

Di-, tri- and tetrasaccharide fragments of the linear chain of the capsular polysaccharide of Streptococcus pneumoniae type 3 consisting of glucose and glucuronic acid residues connected with beta 1----3- and beta 1----4-glycosidic linkage have been synthesised. A new method for selective deprotection of C3-hydroxyl group in the glucopyranuronic acid moiety is proposed.     

Comparative characteristics of soluble and membrane brain aminopeptidases. I. Isolation, physico-chemical properties, catalytic activity

The methods were worked out for isolating of the bovine brain soluble and membrane-bound aminopeptidases in highly purified state. One of the stages involved a biospecific-type chromatography on aminohexyl-Sepharose. Both enzymes were found to have equal molecular masses (ca. 100-107 kD) and isoelectric points (pI 4,6). None of the enzymes possessed a subunit structure. Both aminopeptidases were inactivated by omicron-phenanthroline and by an SH-reagent, p-hydroxymercuribenzoate. The catalytic constants for the hydrolysis of a specific substrate, L-leucine p-nitroanilide, were identical for the two enzymes. So far no differences in the physico-chemical or enzymatic properties of the soluble and membrane-bound enzymes were disclosed.