Neuronal porosome in the rat and cat brain

It is well established that during cell secretion, membrane-bound secretory vesicles dock and fuse at the base of supramolecular cup-shaped structures at the cell plasma membrane called “porosomes”, to expel intra-vesicular contents to the outside. In neurons, it has been demonstrated that 12–17 nm cupshaped lipoprotein structure possessing a central plug are present at the presynaptic membrane, where 50 nm in diameter synaptic vesicles transiently dock and fuse to release neurotransmitters. In the past decade, the neuronal porosome has been isolated and its major chemical composition determined. Additionally, the porosome has been both structurally and functionally reconstituted into artificial lipid membrane, establishing its role as the secretory portal in neurons. Studies utilizing atomic force and electron microscopy, combined with electron density and 3D contour mapping, provide at the nanoscale, the structure and assembly of proteins within the neuronal porosome. In the current study, ultrahigh resolution imaging of the presynaptic membrane of isolated brains from both rats and cats, demonstrate for the first time, the presence of neuronal porosomes in cat brain, and further confirms the presence of porosomes at the presynaptic membrane in rat brain synaptosomes. Results from the present study further confirm the cup-shaped morphology of porosomes in the rat brain, and demonstrates their similar shape and size in the cat nerve terminal. The study also demonstrates for the first time, the universal presence of similar porosomes in different species of mammals.     

Interaction of a cationic polymer with negatively charged proteoliposomes

In the present study, we have analyzed a previously identified constitutively active pituitary adenylate cyclase activating polypeptide (PACAP) type I (PAC1) receptor with a deletion of the single amino acid residue Glu(261) (Y.-J. Cao, G. Gimpl, F. Fahrenholz, A mutation of second intracellular loop of pituitary adenylate cyclase activating polypeptide type I receptor confers constitutive receptor activation, FEBS Lett. 469 (2000)). This glutamic acid residue is highly conserved within the second intracellular loop of class II G protein-coupled receptors and may thus be of importance for many members of this receptor class. To explore the molecular characteristics of this mutant receptor, we performed photoaffinity labeling using previously defined photoreactive PACAP analogues. In COS cells, the PAC1 receptor was expressed in two differently glycosylated forms: a M(r) 75,000 and a M(r) 55,000 form. According to partial deglycosylation, at least three carbohydrate chains may exist in the rat PAC1 receptor expressed in COS cells. The constitutively active PAC1 receptor was expressed at the surface of COS-7 cells at the same density as the wild-type receptor. With respect to the different photoreactive PACAP analogues, the labeling specificity was the same for the wild-type versus mutant receptor: (125)I-[Lys(15)(pBz(2))]-PACAP-27 and (125)I-[Bpa(22)]-PACAP-27 were efficiently incorporated into each of the receptors, whereas (125)I-[Bpa(6)]-PACAP-27 labeled each of the receptors only to a negligible extent. This suggests that both receptors have the same or at least a very similar hormone binding site which is in close contact to Tyr(22) and Lys(15) located in the carboxy-terminal alpha-helical region of the PACAP-27 molecule. However, in comparison with the wild-type PAC1 receptor, the constitutively active receptor showed a markedly (approx. 6--8-fold) enhanced photoaffinity labeling efficiency in particular of the high glycosylated form. The enzymatically deglycosylated rat PAC1 receptor was efficiently labeled by photoreactive PACAP analogues. In contrast, nonglycosylated PAC1 receptors produced by tunicamycin treatment of the transfected COS-7 cells showed a 30-fold lower affinity for PACAP-27 and were capable of signal transduction with 30--50-fold lower potency as compared with the glycosylated PAC1 receptors.     

Spatial synchronization of cerebral cortical potentals at different levels of functioning of short-term verbal memory]

Spatial synchronization of cortical biopotentials was studied at different levels of the functioning of short-term verbal memory. In the phases prior to and during presentation of information the general level of distant synchronization in the cortex at a high functional state of the mnemical mechanism is higher than at a low state. In the phases following presentation and during reproduction, the relations are reverse. The enhancement of distant synchronization involves primarily the posterior parts of the right hemisphere, while the decrease comprises all the cortical areas, with some predominance of this effect in the anterior areas.     

Study of cytotoxicity of fullerene C60 derivatives

We investigated the cytotoxicity of the fullerene C₆₀ derivatives. We showed that complexes of C₆₀ fullerene with polyvinylpyrrolidone (m.w. of polyvinylpyrrolidone 10000 and 25000), C₆₀-NO₂-proline and C₆₀-alanine had no toxic effect on HEp-2 cells. Sodium salt of polycarboxylic derivative of fullerene C₆₀ exerted a pronounced toxic effect on this cell culture.