Effects of noradrenaline and the blood perfusion rate on the oxygen consumption of intact and isolated muscles of cold-acclimated rats

The authors studied the effect of the blood perfusion rate and of noradrenaline (NA) on the oxygen consumption of the isolated hind limb and on the partly - and vascularly completely - isolated cranial gracilis muscle of cold-acclimated rats. Oxygen consumption of the limb was stimulated by a raised perfusion rate together with growth of the oxygen extraction coefficient and by NA, which also raised oxygen consumption when the perfusion rate was constant. Oxygen consumption of the partly isolated muscle was likewise stimulated by a raised perfusion rate, but without a simultaneous increase in the oxygen extraction coefficient. In the vascularly completely isolated muscle, a raised perfusion rate had only a transient stimulant effect on oxygen consumption. In the partly and the completely isolated muscle, NA raised the arteriovenous difference in the blood oxygen content and organ resistance independently of each other. The calorigenic effect of NA, which was determined by the ratio of the two effects, did not exceed 34% above the resting level. The conclusions that the thermogenesis of resting muscle can be controlled by the blood flow on the basis of a mechanism other than the limitation of oxygen or substrates supply, and that NA acts independently of oxygen extraction from the blood and of the blood flow, show the blood flow to be a mechanism at organ level, which participates in the control of nonshivering thermogenesis in skeletal muscle.     

Study of membrane potential changes of yeast cells caused by Killer Toxin K1

This work was supported by the NATO Linkage Grant H TECH.LG 930 686.     

Parsing recursive sentences with a connectionist model including a neural stack and synaptic gating

It is supposed that humans are genetically predisposed to be able to recognize sequences of context-free grammars with centre-embedded recursion while other primates are restricted to the recognition of finite state grammars with tail-recursion. Our aim was to construct a minimalist neural network that is able to parse artificial sentences of both grammars in an efficient way without using the biologically unrealistic backpropagation algorithm. The core of this network is a neural stack-like memory where the push and pop operations are regulated by synaptic gating on the connections between the layers of the stack. The network correctly categorizes novel sentences of both grammars after training. We suggest that the introduction of the neural stack memory will turn out to be substantial for any biological ‘hierarchical processor’ and the minimalist design of the model suggests a quest for similar, realistic neural architectures.     

Generation of scFv phages specific to Staphylococcus enterotoxin C1 by panning on related antigens

A method for generation of highly specific miniantibodies within the phage particle has been developed and used to produce antibodies against Staphylococcus enterotoxin type C1. Under successive panning of the non-immune phage miniantibody (scFv) library with enterotoxins SE (types A, B, C1, D, E, G and I) adsorbed on the plate surface, we generated 11 individual phage clones to Staphylococcus enterotoxin type C1. Five of them interacted specifically only with SEC1 and had no cross-reactions with the other enterotoxins.Key words: scFv, phage display, antibody specificity, Staphylococcus aureus enterotoxins     

Penetrating Cations Enhance Uncoupling Activity of Anionic Protonophores in Mitochondria

Protonophorous uncouplers causing a partial decrease in mitochondrial membrane potential are promising candidates for therapeutic applications. Here we showed that hydrophobic penetrating cations specifically targeted to mitochondria in a membrane potential-driven fashion increased proton-translocating activity of the anionic uncouplers 2,4-dinitrophenol (DNP) and carbonylcyanide-p-trifluorophenylhydrazone (FCCP). In planar bilayer lipid membranes (BLM) separating two compartments with different pH values, DNP-mediated diffusion potential of H⁺ ions was enhanced in the presence of dodecyltriphenylphosphonium cation (C₁₂TPP). The mitochondria-targeted penetrating cations strongly increased DNP- and carbonylcyanide m-chlorophenylhydrazone (CCCP)-mediated steady-state current through BLM when a transmembrane electrical potential difference was applied. Carboxyfluorescein efflux from liposomes initiated by the plastoquinone-containing penetrating cation SkQ1 was inhibited by both DNP and FCCP. Formation of complexes between the cation and CCCP was observed spectophotometrically. In contrast to the less hydrophobic tetraphenylphosphonium cation (TPP), SkQ1 and C₁₂TPP promoted the uncoupling action of DNP and FCCP on isolated mitochondria. C₁₂TPP and FCCP exhibited a synergistic effect decreasing the membrane potential of mitochondria in yeast cells. The stimulating action of penetrating cations on the protonophore-mediated uncoupling is assumed to be useful for medical applications of low (non-toxic) concentrations of protonophores.     

Novel functions of Noggin proteins: inhibition of Activin/Nodal and Wnt signaling

The secreted protein Noggin1 is an embryonic inducer that can sequester TGFβ cytokines of the BMP family with extremely high affinity. Owing to this function, ectopic Noggin1 can induce formation of the headless secondary body axis in Xenopus embryos. Here, we show that Noggin1 and its homolog Noggin2 can also bind, albeit less effectively, to ActivinB, Nodal/Xnrs and XWnt8, inactivation of which, together with BMP, is essential for the head induction. In support of this, we show that both Noggin proteins, if ectopically produced in sufficient concentrations in Xenopus embryo, can induce a secondary head, including the forebrain. During normal development, however, Noggin1 mRNA is translated in the presumptive forebrain with low efficiency, which provides the sufficient protein concentration for only its BMP-antagonizing function. By contrast, Noggin2, which is produced in cells of the anterior margin of the neural plate at a higher concentration, also protects the developing forebrain from inhibition by ActivinB and XWnt8 signaling. Thus, besides revealing of novel functions of Noggin proteins, our findings demonstrate that specification of the forebrain requires isolation of its cells from BMP, Activin/Nodal and Wnt signaling not only during gastrulation but also at post-gastrulation stages.     

iTRAQ-based proteomic study of the effects of microcystin-LR on medaka fish liver

Microcystins are cyanotoxins that occur in ground water and thus pose a potential health risk. Microcystin-LR (microcystin-leucine-arginine) is a potent hepatotoxin, and is suspected of being a tumour promoter. Poisoning with this toxin causes several dysfunctions in hepatocytes by inhibiting protein phosphatases 1 and 2A, and notably produces oxidative stress, disrupts the cytoskeleton, and deregulates mitogen-activated protein kinase pathway. Medaka fish (Oryzias latipes) was chosen as a model for studying the effects of this cyanotoxin on liver proteins using a gel-free approach, iTRAQ. Fish were gavaged with microcystin-LR. Two hours later, 325 proteins could be identified by Scaffold Q+ and 32 proteins revealed statistically significant variations above a ∣0.2∣ threshold of log(2) ratio by comparison with control. These proteins are mostly involved in the translation and maturation of proteins, lipid metabolism and detoxification. Notably, apolipoproteins are deregulated which indicates a possible alteration of chylomicron-mediated transport.