Localization of the nerve growth factor receptor on fetal human schwann cells in culture

Previous studies have established that Schwann cells (SC) in culture express an NGF receptor. In this study, cultures of fetal human SC were established from fetal nerves and various light microscopic (LM) and electron microscopic (EM) techniques were used to localize the NGF receptor on the SC. Results indicate that NGF receptor is localized to the plasma membrane of the SC. Quantitative digital analysis determined that the distal portion of the SC process had high concentrations of NGF receptor. The possible functional significance of this latter observation is discussed in terms of SC migration and ensheathment of axons.     

Inhibition of red cell Ca2+-dependent K+ channels by snake venoms

We have investigated the effects of several snake venoms on the Ca2+-dependent K+ channels of human red cells. A heat-resistant component of the venom of the snake Notechis scutatus irreversibly inhibited Ca2+-dependent K+ transport with a Ki value of 0.1-0.2 micrograms/ml. Metabolic changes of the cells modified the maximal effect of the venom. Binding of the venom required extracellular Ca2+ and was quick, but development of full inhibition required additional time. The effects of the venoms from Notechis scutatus and Leiurus quinquestriatus were additive, suggesting that both venoms act through different mechanisms. Venoms of the snakes Vipera russelli russelli and Oxyuranus scutellatus also inhibited Ca2+-dependent K+ transport with the same characteristics as the Notechis scutatus venom.     

Histochemical detection of monoamine oxidase and alcohol dehydrogenase activities in the Syrian hamster Harderian glands: existence of a sexual dimorphism

Summary Monoamine oxidase (MAO) and alcohol dehydrogenase (AD) activities were studied histochemically in the Syrian hamster Harderian gland using tryptamine as substrate and Nitroblue Tetrazolium as the final electron acceptor. No dark: light-related changes were observed. Male type I secretory cells showed an intense MAO reaction. Female type I cells exhibited a moderate MAO activity. Both male and female glands showed a moderate/intense AD-positive reaction. Male type II cells were lacking MAO and AD activities. MAO activity found in the hamster Harderian glands corresponded mainly to MAO type A since treatment with chlorgyline (0.01, 0.1 and 0.5mm) totally inhibited it. The possible role of these two enzymes in Harderian gland indolalkylamine metabolism is discussed.     

Size variation in Brachionus plicatilis resting eggs

The effect of temperature and salinity on resting egg size of two Brachionus plicatilis (Rotifers) clones was investigated. Clones were selected according to their different behaviour in laying resting eggs: one clone ejects them, whereas they remain inside the females body in the other clone. The difference in resting eggs size between the two clones is noticeable, although the difference is not as great as that between female body size. An important temperature-salinity interaction on resting egg size has been observed. The general inverse relationship between size and temperature is only true at lower temperatures. At high temperatures size varies around the mean although could be greater than at intermediate temperatures. This is more evident at the intermediate salinity tested which is considered to be the closest to the optimum in our experiments. This pattern of variation suggests that mean size is bigger than expected, in relation to temperature and salinity, when these factors have values close to the extremes of their range, normally found in nature, and to which adaptative mechanisms can evolve. Size is bigger at the salinity — temperature low - low and high - high combinations which are the most commonly found in the temperate environments.     

Dicarboxylic acid anhydrides as dissociating agents of protein-containing structures

Dissociation of protein-containing structures by modification of protein amino groups with dicarboxylic acid anhydrides is a mild procedure which, in some cases, offers advantages over treatment with alternative dissociating agents, such as urea, guanidine hydrochloride, detergents, high ionic strength, and extremes of pH: In addition to dissociating multimeric proteins and protein aggregates, dicarboxylic acid anhydrides are effective dissociating agents for membrane-bound proteins and nucleoprotein particles. With most dicarboxylic acid anhydrides reviewed, the introduced reagent residues can be eliminated under moderate acid conditions, which allows the purification of unmodified individual components, and the use of disassembly-reconstitution systems valuable for investigating the structural and functional roles played by the individual components of complex particles:Each reagent can be suitable for a particular purpose, depending on the required specificity of the modification and stability of the modified groups: The stability of the acylated amino groups ranges from the very stable succinylated amino groups to the very labile acylation obtained with dimethylmaleic anhydride: Between these extremes, the stability of the modified amino groups decreases stepwise in the following order: maleic, exo-cis-3,6-endoxo-⁴-tetrahydrophthalic, citraconic, and 3,4,5,6-tetrahydrophthalic anhydride. With respect to the selectivity of the produced modification, little or no modification of hydroxyamino acid and cysteine residues has been observed with dimethylmaleic, exo-cis-3,6-endoxo-⁴-tetrahydrophthalic, and 3,4,5,6-tetrahydrophthalic anhydrides: With the other reagents, the extent of modification of hydroxyamino acid residues increases in the order citraconic, maleic and succinic anhydride: Citraconic and maleic anhydrides can produce irreversible modification of cysteine residues, the reactivity of sulfhydryl groups being higher with maleic anhydride:     

Analysis of polyadenylated RNA from brain synaptosomes and mitochondria

We have isolated RNA from sheep brain synaptosomes and mitochondria separated by an aqueous two-phase system composed of dextran and poly(ethylene glycol). RNA was fractionated through oligo(dT)-cellulose columns and analyzed by electrophoresis through agarose slab gels containing methylmercuric hydroxide and stained with ethidium bromide. The electrophoretic patterns of the poly(A)-containing RNA fraction from synaptosomes and mitochondria are very similar although some high molecular weight RNA species, clearly visible in the synaptosomal fraction, are scarcely detected in the mitochondrial preparations. The electrophoretic analysis of a cleaner RNA preparation from digitonin-treated free mitochondria (mitoplasts) showed that all the poly (A)-RNA species of the synaptosomal preparation are also present in mitoplast. These results strongly suggest that all the discrete poly(A)-RNA species identified in brain synaptosomes are of mitochondrial origin.     

Prothymosin alpha expression is associated to cell division in rat testis

Summary Using immunohistochemical methods, we have investigated the cellular distribution of prothymosin alpha (ProT) in adult rat testis. A policlonal antibody raised against thymosin alpha 1 conjugated to keyhole limpet hemocyanin was used. ProT immunoreactivity was observed in the cytoplasm and nucleus of spermatogonia and primary spermatocytes in initial phases of the first meiotic division, preleptotene, leptotene and zygotene. However, in pachytene phase they already showed a weak or negative staining. On the other hand, secondary spermatocytes, spermatids, spermatozoa and Sertoli cells were not stained. Based on this fact we suggest that ProT is present in the proliferative cycle in the final steps of G₁ phase, throughout the S and G₂ phases and in initial steps of the prophase.     

Chemical and enzymic oxidation by tyrosinase of 3,4-dihydroxymandelate.

Tyrosinase usually catalyses the conversion of monophenols into o-diphenols and the oxidation of diphenols to the corresponding o-quinones. Sugumaran [(1986) Biochemistry 25, 4489-4492] has previously proposed an unusual oxidative decarboxylation of 3,4-dihydroxymandelate catalysed by tyrosinase. Our determination of the intermediates involved in the reaction demonstrated that 3,4-dihydroxybenzaldehyde is not the first intermediate appearing in the medium during the enzymic reaction. Re-examination of this new activity of tyrosinase has demonstrated that the product of the enzyme action is the o-quinone, which, owing to its instability, evolves to the final product, 3,4-dihydroxybenzaldehyde, by a chemical reaction of oxidative decarboxylation.     

Ca2+ ionophores inhibit superoxide generation by chemotactic peptide in rabbit neutrophils and the correlation with intracellular calcium

Summary Effects of Ca²⁺ ionophores, A23187 and lasalocid, on superoxide anion generation by chemotactic peptide, N-formyl-methionyl-leucyl-phenylalanine methyl ester, in rabbit peritoneal exudate neutrophils were studied. The ionophores by themselves did not activate superoxide anion generation in these neutrophils. When preincubated with the cells for 2 min, both the ionophores inhibited superoxide generation induced by chemotactic peptide. The inhibition was present even in the absence of extracellular Ca²⁺ and the inhibition was better then. Lasalocid produces a dose-dependent chlortetracycline fluorescence decrease response in neutrophils loaded with chlortetracycline. This response is independent of extracellular Ca²⁺ concentration and is related to release of Ca²⁺ from intracellular storage sites. The dose-range at which lasalocid gives this response is same as the dose-range at which it causes inhibition of superoxide response. It may be concluded that the inhibition of superoxide generation by these ionophores is correlated to intracellular Ca²⁺ modulation.Abbreviations FMLP Formyl-Methionyl-Leucyl-Phenylalanine methyl ester     

Metabolic adaptation of the renal carbohydrate metabolism. I. Effects of starvation on the gluconeogenic and glycolytic fluxes in the proximal and distal renal tubules

Summary The influence of starvation on renal carbohydrate metabolism was studied in the proximal and distal fragments of the nephron. Starvation induced a double and opposite adaptation mechanism in both fractions of the renal tubule. In renal proximal tubules, the gluconeogenic flux was stimulated progressively during a period of 48 hours of starvation (2.15 fold), due, in part, to a significant increase in the fructose 1,6-bisphosphatase and phosphoenolpyruvate carboxykinase activities although with different characteristics. Fructose 1,6-bisphosphatase activity from this tubular fragment increased only at subsaturating subtrate concentration (68%) which involved a significant decrease in the Km (35%) for fructose 1,6-bisphosphate while there was no change in Vmax. This behaviour clearly indicates that it is related to modifications in the activity of the preexistent enzyme in the cell. Proximal phosphoenolpyruvate carboxykinase activity increased proportionally at both substrate concentrations (86 and 89% respectively) which brought about changes in Vmax without changes in Kin, all of which are in accordance with variations in the cellular levels of the enzyme. In the renal distal tubules, the glycolytic capacity drastically decreased throughout the starvation time. At 48 hours 65% of inhibition was shown. We have found a short term regulation of phosphofructokinase activity by starvation which involves an increase in Km (2.2 fold) without changes in Vmax, as a result of these kinetic changes, an inactivation of phosphofructokinase was detected at subsaturating concentration of fructose 6-phosphate. On the contrary, this nutritional state did not modify the kinetic behaviour of renal pyruvate kinase. Finally, neither proximal glycolytic nor distal gluconeogenic capacities and related enzymes activities were changed during starvation.