A kinetic analysis of the inward calcium current in 108CC15 neuroblastoma x glioma hybrid cells

The kinetics of activation and inactivation of the inward calcium current (ICa) in morphologically undifferentiated and differentiated neuroblastoma X glioma hybrid cells of the clone 108CC15 were studied by the suction pipette technique for internal perfusion and voltage clamping. Potassium currents were eliminated by internal perfusion of the cells with a K+-free solution. Activation of ICa followed a sigmoidal time course and could reasonably be fitted by a m2 relation. The kinetics of ICa inactivation were studied by analyzing the current inactivation during long depolarizing steps and by measuring the peak ICa as a function of the length of a prepulse. Both methods gave comparable results indicating that the ICa inactivation cannot be fitted by a single exponential. The ICa inactivation was fitted by a biexponential function. Neither the activation nor the inactivation of ICa were changed after morphological cell differentiation induced by treatment with dibutyryl cyclic AMP.     

Lactose-proton symport by purified lac carrier protein

The lac carrier protein of Escherichia coli was purified by an improved procedure and its activity assayed by a rapid filter method. Following reconstitution of the carrier by octyl glucoside dilution, proteoliposomes were concentrated by filtration on a microporous filter. Lactose accumulation by adsorbed or entrapped proteoliposomes is driven by an artificially imposed pH gradient (interior alkaline), by a membrane potential (interior negative), or by a combination of both forces. Activity is almost completely abolished by the protonophore carbonyl cyanide m-chlorophenylhydrazone or by the competitive inhibitor thiodigalactoside. Addition of lactose to proteoliposomes under appropriate conditions results in alkalinization of the external medium. This effect is not observed with liposomes devoid of lac carrier or in the presence of proton conducting agents. The results provide a strong indication that the lac gamma gene product is the only protein in the cytoplasmic membrane of Escherichia coli required for lactose-proton symport.     

Factors influencing swimming in bay scallops, Argopectenirradians (Lamarck, 1819)

Factors influencing the probability, distance, and direction of swimming in bay scallops (Argopectenirradions Lamarck, 1819) were studied through a series of experimental releases in the field and in a 3-m tank. The probability of a scallop swimming was significantly influenced by the type of substratum on which it was released (sand vs. grassbed), by contact with two natural gastropod predators (Murex, Fasciolaria), and by the amount of rest allowed after a previous swim. The horizontal distance traveled by a swimming scallop was significantly influenced by artificial weight of a magnitude equivalent to a normal load of shell-encrusting organisms, by the amount of rest allowed after a previous swim, by the height attained in the water column, and by the scallop's size. The direction of scallop swimming was significantly influenced by the location along the mantle edge where a predator was contacted, and by factors probably related to the asymmetrical water flow pattern through the mantle cavity. Swimming in bay scallops apparently serves to maintain position in grassbeds and to avoid predators.     

Effect of uncoupling treatments on FSH-induced hyperpolarization of immature rat Sertoli cells from Sertoli cell-enriched cultures

Sertoli cell-enriched cultures isolated from immature rat testes by enzymic treatments were investigated by intracellular microelectrode recordings. The hyperpolarization of cells induced by FSH was independent of the age of the rats (7-37 days) and was unchanged by exposure to a hormone-free medium or to a glycine buffer of pH 3. It was reduced by treatments which decreased the electrical coupling between cells either by an increase of intracellular calcium [i.e. calcium ionophore (A 23187, 5 x 10(-6) M), general anaesthetic (heptanol, 3.5 mM) and uncoupler of oxidative phosphorylations (carbonylcyanide m-chlorophenylhydrazone-CCmP, 10(-6) M)] or by a decrease of extracellular calcium [i.e. 0Ca + EGTA (1 mM) medium]. These effects were partly or totally reversed by a recovery period in a drug-free medium. Similar results were obtained by an exposure to trypsin (0.05%) followed by a second mechanical dispersion, but new cell hyperpolarization was induced by a new exposure to FSH. This electrophysiological study suggests an initial effect of FSH on the junctional complex between Sertoli cells, then the control by calcium of this complex.     

Preferential assignment of allotype a1 globulin for the production of early IgM anti-para-azobenzenearsonate antibodies in heterozygous a1a3 rabbits.

Rabbits of allotype a1a3 were injected on days 0, 2, and 4 with mixtures containing equal amounts of pigeon erythrocytes (Prbc) coupled to para-azobenzenearsonate (AA) and to para-azobenzene-N-trimethylammonium (TMA). On day 6, the allotypes of antibody from plaque-forming cells (PFC) of the blood were determined by observing the inhibition of plaque formation by anti-allotype sera. Anti-AA PFC appeared to consist for the most part of cells making antibody of allotype a1 since 65% of them were inhibited by anti-a1 serum and only 8% by anti-a3. Anti-TMA PFC, on the other hand, appeared to consist mostly of cells making antibody of allotype a3, since less than 1% of them were inhibited by anti-a1 but 47% by anti-a3. Antibody allotype for spleen PFC was also determined on day 6 and was similar to that found for blood PFC. Anti-AA PFC were inhibited 74% by anti-a1 serum and 15% by anti-a3 whereas anti-TMA PFC were inhibited 19% by anti-a1 and 43% by anti-a3. Serum hemolysin specific for AA hapten from a1a3 animals was also strongly inhibited by anti-a1 serum but not by anti-a3 whereas the converse was true for hemolysin against TMA hapten. The a1a3 rabbits, in whcih the anti-AA was restricted to allotype a1, were mated to produced homozygous a3a3 animals. When the PFC and serum antibodies of these a3a3 offspring were examined by specific inhibition, the anti-AA activity was found to be of allotype a3 rather than being a-negative. The number of anti-AA PFC in the blood of a3a3 rabbits was lower than that in blood of a1a3 or a1a1 animals. In addition, the TMA hapten appeared to inhibit the response to the AA hapten. Thus a1a3 rabbits immunized with AA-Prbc alone had 14-fold more anti-AA PFC or 18-fold higher anti-AA hemolysin titer than a3a3 animals immunized with both AA-Prbc and TMA-Prbc. Our results are discussed in relation to various explanations which have been offered for an imbalance of allotypes in a given antibody.     

Three-dimensional reconstruction of maltoporin from electron microscopy and image processing.

Two dimensional crystals of maltoporin (or phage lambda receptor) were obtained by reconstitution of purified maltoporin trimers and Escherichia coli phospholipids by detergent dialysis. Two different trimer packing forms were observed. One was hexagonal (a = 7.8 nm) and one rectangular (a = 7.8 nm, b = 13.6 nm). In this paper we describe the three-dimensional structure of maltoporin, deduced from the study of the rectangular form by electron microscopy and image processing. At a resolution of approximately 2.5 nm, maltoporin trimers form aqueous channel triplets which appear to merge into a single outlet at the periplasmic surface of the outer membrane. The pore defined by maltoporin has a similar structure to that outlined by the matrix protein. From the results of functional studies by conductance measurement, it is concluded that the three channels defined by maltoporin act, contrary to those formed by the porin (OmpF protein), as a single conducting unit. A tentative outline of the maltoporin promoter is given. Maltoporin appears to be constituted by three different domains: a major rod-like domain spanning the membrane, a minor domain located near the periplasmic surface of the membrane and finally a central domain responsible for the splitting of the channel.     

Technique of surface modification of a cell-adhesion-resistant hydrogel by a cell-adhesion-available inorganic microarray

A microtransfer technique for micropattern fabrication using a dithiol macromolecular linker is suggested by transferring a conventionally photolithography-prepared gold microarray on a hard inorganic substrate to a polymeric substrate. The linker was synthesized by end-capping a poly(ethylene glycol) (PEG) chain by the thiol groups. The efficiency of this technique is demonstrated by the transfer of gold microdots from glass to a cell-adhesion-resistant PEG hydrogel, which was formed by polymerizing PEG diacrylate macromers. The stability and biocompatibility of the resulting polymeric-inorganic hybrid material and cell-adhesion contrast of the patterned surface is confirmed by preliminary cell experiments.     

Regulation of DNA synthesis in mouse macrophages. II. Studies on mechanisms of action of the macrophage growth factor

When mouse macrophages are incubated with medium conditioned by mouse fibroblasts, they are induced to synthesize DNA and divide. This phenomenon is triggered by a macrophage growing factor (MGF) released by the fibroblasts. The presence of a serum cofactor is essential to the activity of the MGF; this cofactor can be removed by dialysis and seems unrelated to the “growth-promoting substances” normally present in serum. The kinetics of DNA synthesis in macrophages stimulated by conditioned medium (CM) is characterized by a lag phase of 24–48 h and a peak synthesis at 4–5 days, followed by a rapid decrease. This decrease is caused by depletion of the MGF from the CM by the growing macrophages.     

Importance of patient selection in evaluating a cardiac ambulance service.

All patients brought to hospital by a special cardiac ambulance were followed up and compared with patients carried by routine ambulances to assess the effectiveness of a cardiac ambulance service. The overall mortality of patients with heart attacks was 51% among those carried by an ordinary ambulance and 40% among those carried by the cardiac ambulance. The apparently low mortality in the latter group was balanced, however, by a high mortality (68%) among patients carried by ordinary ambulances when the cardiac ambulance was available but not used; these patients tended to have a short duration of symptoms and heart attacks away from home, and their ambulance was more often called by a member of the public than a general practitioner. It seems therefore that low-risk cases were inadvertently selected for transport by the cardiac ambulance; such unintentional selection makes it difficult to evaluate a cardiac ambulance service.     

Generation of a wakefield during gas ionization

One-dimensional equations are derived that describe the hydrodynamic and electrodynamic properties of a plasma created through gas ionization by a short intense laser pulse. Different approaches (in particular, the particle-in-cell method) are used to show that, with ionization processes included, the excitation of a wakefield by an intense laser pulse can be described by the method of slowly varying amplitudes. It is shown that ionization processes enhance the wakefield excited by a moderate-intensity laser by about 10% in the case of a linearly polarized laser and by about 50% in the case of a circularly polarized laser. Ionization processes in light gases irradiated with high-intensity laser pulses have essentially no effect on the wakefield during the resonant excitation of a plasma wave by the ponderomotive force and play a governing role far from the resonance.     

Potentially infanticidal behavior in the Amazon river dolphin (<Emphasis Type="Italic">Inia geoffrensis</Emphasis>)

Infanticide by males is a phenomenon common in species in which the reproductive output of large numbers of females can be monopolized by a small number of males. It is thought to increase a male’s fitness, at the expense of the fitness of the infant’s parents, by bringing females into season more quickly. Infanticide by males has been recorded in just three cetacean species. We report aggressive behavior suggestive of infanticide in a fourth, the Amazon river dolphin (Inia geoffrensis). We observed and photographed a series of attacks on a neonate Amazon river dolphin by a large male, with apparent protective behavior by the mother. Although infanticide was not confirmed, the forceful, aggressive behaviors were highly suggestive of infanticidal behavior and represent another important data point for comparative studies of infanticide in mammals. Amazon river dolphins may have a polygynous, polyandrous, or promiscuous mating system, the latter two of which are not the norm in species in which the reproductive output of large numbers of females are monopolized by a small number of males. However, sexual dimorphism, high rates of aggression by males, socio-sexual object-carrying displays by males, and a long interbirth interval suggest that successful male Amazon river dolphins may be able to monopolize a large proportion of mating opportunities, and it is plausible that male dolphins can improve their reproductive success by bringing females into estrous sooner by killing the offspring of other males.     

植物群落的冗余结构——对生态系统稳定性的一种解释

应用冗余理论探讨植物群落的稳定性机理。植物群落的冗余是由植物体的器官冗余、种群内遗传结构冗余、物种冗余和层次冗余组成的。植物群落的抵抗力主要来自物种冗余和种群内遗传结构冗余,而恢复力来自层次冗余和器官冗余。植物群落的冗余结构决定了其稳定性是抵抗的,或是恢复的,或即是抵抗的又是恢复的。研究表明,冗余理论比多样性导致稳定性更能合理地解释植物群落的稳定性。植物群落冗余按其组成万分的性质可分为两种：数量冗     

Studies on apple protopectin. IV: Apple xyloglucans and influence of pectin extraction treatments on their solubility

Hemicelluloses were extracted from apple cell walls with 1 and 4 sodium hydroxide and 8 urea after depectinisation by a chelating agent, by a chelating agent and dilute sodium hydroxide or by a chelating agent and a pectin-lyase. The extracts were fractionated on Sephacryl S 500 and DEAE Sepharose CL-6B. The bulk of the hemicelluloses were solubilised by 4 sodium hydroxide. The main hemicellulose was a fucogalactoxyloglucan. Some low-molecular-weight mannans were also present. Part of the xyloglucans could be extracted by urea after pectin extraction by a chelating agent or by pectin-lyase but not after pectin extraction by dilute sodium hydroxide. Dilute sodium hydroxide probably insolubilised some of the pectins and hemicelluloses.     

The use of a cyanine dye in measuring membrane potential in yeast

An attempt was made to use 3,3'-dipropylthiacarbocyanine as a membrane potential probe in yeast by following both its fluorescence changes and its uptake by the cells under different conditions. It was found that the uptake of the dye into the cytoplasmic compartment was translated into an increased fluorescence, and the uptake by the mitochondria produced a quenching of the fluorescence. The experiments to measure uptake showed that a large amount of the dye was taken up by the cells under "deenergized" conditions. The uptake of the cyanine, however, was significantly reduced by the omission of the substrate, by deenergization of the mitochondria, or by the addition of K+, but not by Na+. This cyanine seems to be a good, qualitative indicator of the potential of the plasma membrane and of the mitochondria of the cells, with a faster response than those probes used before in yeast.     

The predatory legs of Philonthus marginatus (Coleoptera, Staphylinidae): functional morphology and tarsal ultrastructure

Representatives of the staphylinid beetle Philonthus marginatus are characterized by highly modified raptorial forelegs which are used to strike prey in a particularly fast manner. Beetles ready to capture prey remain in a characteristic precapture ambush posture characterized by lifted and folded forelegs. Triggered by sensory input from the antenna or other parts of the fore body, the actual strike is released, essentially taking the form of a rapid (about 9 ms) depression of the unfolding forelegs towards the prey. This movement is based on the presence of a coxo-trochanteral catch mechanism and a particularly wide angle of rotation in the coxo-trochanteral joint. It is made possible by the specific mechanics of this joint which probably also involves a co-contraction of the antagonistic trochantero-femoral flexor and extensor muscles suggesting a spring-loaded system. This phase of the strike is immediately followed by fixation of the prey by the ventral adhesive tarsal setae supported by a grasp of the flexing last tarsomere and the claws. After withdrawal of the forelegs together with the prey, the sequence eventually results in the formation of a capture-basket formed frontally by the perpendicularly flexing head and laterally by the spiny inner sides of the coxae.     

Hydrodynamics-based transfection of the liver: entrance into hepatocytes of DNA that causes expression takes place very early after injection

BACKGROUND: The mechanism of gene transfer into hepatocytes by the hydrodynamics-based transfection procedure is not clearly understood. It has been shown that, after a hydrodynamic injection, a large proportion of plasmid DNA remains intact in the liver where it is bound to plasma membrane and suggested that this DNA could be responsible for the efficiency of the transfection. METHODS: We have investigated the problem by giving mice a hydrodynamic injection of isotonic NaCl, followed at different time intervals by a conventional injection of DNA, cold or labelled with (35)S, with cDNA of luciferase as a reporter gene. Then, we determined the consequences of that dual injection on luciferase expression and on DNA uptake by the liver and its intracellular fate. By such experiments, it is possible to establish the time dependency of the induction of liver changes caused by a hydrodynamic injection on the one hand and the expression and DNA uptake and fate on the other. Moreover, some experiments have been performed on primary cultures of hepatocytes isolated after a hydrodynamic injection of DNA. RESULTS: When DNA is given to mice by a conventional injection a few seconds after an hydrodynamic injection of isotonic NaCl, luciferase expression in the liver is considerably lower than that observed after a single hydrodynamic injection of the plasmid. On the other hand, as assessed by the rate of DNA degradation and by centrifugation results obtained after injection of (35)S-DNA, the uptake and the intracellular fate of the bulk of DNA are similar whether DNA is administered by a single hydrodynamic injection or by a conventional injection given up to at least 2 h after a hydrodynamic injection of isotonic NaCl. Hepatocytes isolated a few minutes after a hydrodynamic injection exhibit a maximal expression that does not depend on the large amount of DNA that remains bound to the plasma membrane for a relatively long time. CONCLUSIONS: Our results show that the efficiency of hydrodynamics-based transfection depends on a process that takes place very quickly after injection and is not linked to a delay of DNA degradation and the persistence of a large proportion of DNA bound to hepatocytes of the plasma membrane, strongly suggesting that expression after a hydrodynamic injection is caused by a small proportion of DNA molecules that rapidly enter the cytosol probably by plasma membrane pores generated by the hydrodynamic pressure.     

Mannitol Uptake by Saccharomyces cerevisiae

The uptake of mannitol, a nonmetabolized hexitol, by Saccharomyces cerevisiae was measured. Various characteristics examined include: effects of temperature on uptake, inhibition of uptake by uranyl nitrate, competition for uptake by glucose, counterflow of mannitol by glucose, and the affinity of mannitol for a carrier system as measured by a Michaelis constant. That energy is required for uptake was shown by a decreased uptake in the presence of energy inhibitors, by an increased uptake upon addition of energy sources, and by the absence of uptake under anaerobic conditions with no fermentable energy sources available. That mannitol is bound to some cellular constituent after it enters the cell was shown by its attachment to non-dialyzable cell fragments and by the lack of an osmotic response, both of which are consistent with a minimal efflux.     

Involvement of transforming growth factor-alpha secreted by macrophages in metallothionein induction by endotoxin

The mechanism of metallothionein (MT) induction of the liver by endotoxin, which is mediated by a factor secreted by endotoxin-stimulated macrophages, was studied in vitro. MT induction of the liver cells by the endotoxin-stimulated macrophage conditioned medium was inhibited by a monoclonal antiepidermal growth factor (EGF) / transforming growth factor-alpha (TGF-alpha) receptor antibody, which acts as an antagonist of EGF and TGF-alpha. MT was induced by the substance, which was adsorbed by polyclonal antibody to TGF-alpha, but not by a monoclonal antibody to EGF, in the conditioned medium of endotoxin-stimulated macrophages. These results suggest that TGF-alpha secreted by macrophages is involved in MT induction by endotoxin.     

Correlation between transglutaminase activity and polyamine levels in human neuroblastoma cells. Effect of retinoic acid and alpha-difluoromethylornithine

The human neuroblastoma cell line SK-N-BE can be induced to differentiate by retinoic acid (RA) or by alpha-difluoromethylornithine (DFMO). The former inducer produces neurite outgrowth, 60% reduction of growth rate, overexpression of neural antigens, and enhanced gamma-aminobutyric acid (GABA) and acetylcholinesterase levels. In contrast, DFMO causes cell body elongation, complete growth inhibition, and higher binding of antibodies directed against neuroectodermal antigens. Polyamine metabolism is also differently affected by the two agents. In particular a large spermine catabolism is induced by RA, while DFMO treatment leads to a small increase in the level of this compound. The neural differentiation induced by RA is accompanied by a marked increase in transglutaminase activity and its induction is paralleled by a transient increase of putrescine and spermidine. The putrescine and spermidine depletion determined by DFMO is accompanied instead by a large inhibition of transglutaminase activity. The inhibiting effect of DFMO treatment on transglutaminase is reversed by the addition of 1 mM putrescine to the culture medium. In the presence of both RA and DFMO a mixed morphological and biochemical pattern is observed. The possibility that the expression of transglutaminase associated to cellular differentiation may be modulated by the level of its substrates is also discussed.