STRUCTURE—FUNCTION RELATIONSHIPS OF NA+/K+-PUMPS EXPRESSED INXENOPUSOOCYTES

During the last years we have examined structure—function relationships in the Na⁺/K⁺-ATPase with respect to interactions of the external cations with the pump molecule. We have analysed in voltage-clamp experiments the influence of extracellular Na⁺and K⁺on the current generated by Na⁺/K⁺-pumps expressed inXenopusoocytes. Our results demonstrated that external Na⁺and K⁺have to pass an access channel in the electrical field of the membrane to reach their binding sites. This external access, therefore, is voltage-dependent and is affected by lysine residues within the cytoplasmic N-terminus, by glutamic acid residues in intramembraneous domains, the ouabain sensitivity and phosphorylation by protein kinases.     

Covariation of morphological characters in the Triassic ammonoid Czekanowskites rieberi

The Triassic ammonoid Czekanowskites rieberi displays a covariation of morphological charac ters, which is rather common in ammonoids. Its morphological spectrum ranges from laterally compressed, involute, weakly ribbed forms to depressed, semiinvolute, strongly ribbed forms. In order to study this covariation, fifteen axially cut specimens have been analyzed by means of image analysis, which allows us to obtain the ontogenetic record of radii, area and perimeter of the individual whorl cross-sections. A logarithmic model of growth has been applied. Our data indicate that, owing to the covariation, the radii from the origin to the venter and to the umbil ical seam of a given whorl section vary inversely in order to maintain the relative position of the center of gravity of the whorl cross-section both throughout the ontogeny of single specimens and within the population. This influences hydrostatic parameters, such as the position of the center of mass and the orientation and stability of the shell. Since the ontogenetic record of the angular length of the body chamber is not known, we have calculated those hydrostatic varia bles using two mutually exclusive assumptions: (1) the angular length of the body chamber was constant throughout ontogeny and (2) the volume of the body chamber grew monotonically with the revolution angle. Fluctuations of the three hydrostatic variables were always less important in the first assumption. In any case, the spectrum of, for example, theoretical orien tations is comparable to those observed in the species of present-day Nautilus. The range of adult body-chamber length observed in C. rieberi is much narrower than the theoretical adult body-chamber length calculated under the second assumption which indicates that a certain control over this parameter existed in the natural population, probably in order to maintain a narrow range in orientation and stability. The excess or deficit in soft-body weight was probably compensated by inverse variations in shell-wall weight. The main conclusion is that, despite the extreme morphological variability, hydrostatic and, possibly, hydrodynamic properties of the population remained within narrow limits.     

Reduced Polyteny of Ribosomal RNA Cistrons in Giant Chromosomes of <Emphasis Type="Italic">Drosophila hydei</Emphasis><Superscript>*</Superscript>

The polytenization of rRNA cistrons in Drosophila species is studied in an attempt to follow the course of under-representation of heterochromatic compared with euchromatic chromosome regions.     

THERAPEUTIC STRATEGIES FOR THE INHIBITION OF INDUCIBLE NITRIC OXIDE SYNTHASE—POTENTIAL FOR A NOVEL CLASS OF ANTI-INFLAMMATORY AGENTS

In recent years, NO, a gas previously considered a potentially toxic chemical, has become established as a diffusible universal messenger mediating cell—cell communication throughout the body. In mammals, NO is a recognized mediator of blood vessel relaxation that helps to maintain blood pressure. In the central nervous system NO acts as a non-conventional neurotransmitter and participates in the establishment of long-term plasticity required for memory formation. In addition, NO is responsible for some parts of the host response to sepsis and inflammation and contributes to certain disease states. A number of strategies have emerged with regard to a pharmacological control of pathological NO overproductions. This review will discuss these novel therapeutic approaches that may provide new means for clinical medicine.     

Terrestrial invertebrates inhabiting lowland river floodplains of Central Amazonia and Central Europe: a review

1. Amazonian terrestrial invertebrates produce high population densities during favourable periods and may suffer a drastic decrease during occasional floods and droughts. However, the monomodal, predictable flood pulse of the larger Amazonian rivers favours the development of morphological (respiratory organs, wing‐dimorphism), phenological (synchronization of life cycles, univoltine mode of life), physiological (flooding ability, gonad dormancy, alternating number of developmental stages), and behavioural adaptations (migration, temporal diving) with numerous interactions. 2. In lowlands of Central Europe, the flood pulse of large rivers is less predictable than in Central Amazonia and is superimposed by the seasonal light/temperature pulse (summer/winter regime). Some terrestrial invertebrates show physiological resistance against inundation or drought, phenologies fitting the normal annual rhythm of water level fluctuation (quiescence or diapause of eggs or adult invertebrates), high dispersal ability and migration. However, most species survive simply using a `risk strategy', combining high reproduction rates, dispersal and reimmigration following catastrophic events. 3. The diversity of species in terrestrial invertebrates is lower in lowland riverine ecosystems of Central Amazonia and Central Europe compared with the respective uplands because of flood stress in these systems. However, floodplains in Central Amazonia possess a greater number of endemic species in comparison with Central European floodplains because of long periods of fairly stable climatic conditions in comparison with large palaeoclimatic changes in Central Europe.     

Net biome production of the Amazon Basin in the 21st century

Global change includes multiple stressors to natural ecosystems ranging from direct climate and land‐use impacts to indirect degradation processes resulting from fire. Humid tropical forests are vulnerable to projected climate change and possible synergistic interactions with deforestation and fire, which may initiate a positive feedback to rising atmospheric CO₂. Here, we present results from a multifactorial impact analysis that combined an ensemble of climate change models with feedbacks from deforestation and accidental fires to quantify changes in Amazon Basin carbon cycling. Using the LPJmL Dynamic Global Vegetation Model, we modelled spatio‐temporal changes in net biome production (NBP); the difference between carbon fluxes from fire, deforestation, soil respiration and net primary production. By 2050, deforestation and fire (with no CO₂ increase or climate change) resulted in carbon losses of 7.4–20.3 Pg C with the range of uncertainty depending on socio‐economic storyline. During the same time period, interactions between climate and land use either compensated for carbon losses due to wetter climate and CO₂ fertilization or exacerbated carbon losses from drought‐induced forest mortality (?20.1 to +4.3 Pg C). By the end of the 21st century, depending on climate projection and the rate of deforestation (including its interaction with fire), carbon stocks either increased (+12.6 Pg C) or decreased (?40.6 Pg C). The synergistic effect of deforestation and fire with climate change contributed up to 26–36 Pg C of the overall decrease in carbon stocks. Agreement between climate projections (n=9), not accounting for deforestation and fire, in 2050 and 2098 was relatively low for the directional change in basin‐wide NBP (19–37%) and aboveground live biomass (13–24%). The largest uncertainty resulted from climate projections, followed by implementation of ecosystem dynamics and deforestation. Our analysis partitions the drivers of tropical ecosystem change and is relevant for guiding mitigation and adaptation policy related to global change.     

Identification of candidate volatiles that affect the behavioural response of the malaria mosquito Anopheles gambiae sensu stricto to an active kairomone blend: laboratory and semi‐field assays

Anopheles gambiae Giles sensu stricto (Diptera: Culicidae) is the most important vector of human malaria in sub‐Saharan Africa, affecting the lives of millions of people. Existing tools such as insecticide‐treated nets and indoor‐residual sprays are not only effective, but also have limitations as a result of the development of resistance to insecticides and behavioural adaptations in biting time. Therefore, novel mosquito‐control tools are needed. Odour‐releasing traps have a potential for both trapping and surveillance purposes. Based on the outcome of ex vivo gene expression assays and in vivo electrophysiological assays on hundreds of volatile organic compounds, 29 ‘candidate behaviourally‐disruptive organic compounds' (cBDOCs) are selected, belonging to 10 chemical categories, to be assayed in the laboratory using dual‐choice olfactometers for the ability to modify the ‘attractiveness’ (i.e. significantly more insects being caught in the associated trap) of a basic volatile blend consisting of ammonia, lactic acid and tetradecanoic acid but without additional carbon dioxide. Compounds that either reduce or increase trap catches by the basic blend in the olfactometer experiments are tested under African conditions in choice experiments in a semi‐field facility in Kenya. The release rates of cBDOCs are determined gravimetrically to allow the calculation of aerial concentrations at the trap outlet. Aerial concentrations in the sub‐p.p.m. range are reported for the first time to influence mosquito behaviour. The results of the olfactometer and semi‐field assays generally correspond. Under semi‐field conditions, three compounds, 3‐heptanol (0.025 p.p.m.), 2‐methylpropanal (0.05 p.p.m.) and 4,5‐dimethylthiazole (0.73 p.p.m.), significantly increase trap catches relative to the basic blend consisting of ammonia, lactic acid, tetradecanoic acid and carbon dioxide. 2‐Acetylthiophene, 2‐nonanone and 2‐phenylethanol decrease the number of mosquitoes caught at all concentrations tested under semi‐field conditions. These compounds hold promise as attractants and spatial repellents to be applied in mosquito control programmes.     

Gnathostomulida from Hawaii

As thc second in a series on Gnathostomulida from the Pacific Ocean this paper describes an additional eight species from Hawaii of which four are new to science. All are accommodated within existing genera: Haplognathia asymmetrica sp.n., Haplognathia ruberrima (Sterrer, 1966), Haplognathia rufa sp.n., Cosmognathia arcus Sterrer, 1991, Cosmognathia manubrium sp.n., Pterognathia ctenifera Sterrer, 1970, Pterognathia hawaiiensis sp.n., and Austrognathia novaeze landiae Sterrer, 1991.     

Strategies of passerine migration across the Mediterranean Sea and the Sahara Desert: a radar study

Radar observations of the diurnal timing of bird migration in the Sahara Desert are presented for autumn migration. Study sites were on a transect along the north-south migratory direction. Three groups of birds migrating either during day, evening or night in the northern part of the Western desert in Egypt were identified. The maximum of day and night groups occurred later the further south the study sites were. Based on the distance between sites and the timing of peak migration, birds were flying at an estimated ground speed of about 20 m/s. The maximum of the evening group was at about 21:00 h at all sites. The three groups were classified according to three different strategies of migration across the Mediterranean Sea and the Sahara Desert: (1) the day group of birds performed a non-stop flight across the sea and at least the northern part of the desert; [2] the night group performed an intermittent migratory strategy with stopover at the coast of Egypt to continue migration the next evening; (3) the evening group birds were also intermittent migratory fliers, but they stopped somewhere in the desert after a continuous flight across the sea and part of the desert. About 20% of all migrants are involved in non-stop migration and 80% in intermittent migration with stopover at the coast (70%) or with stopover in the desert (10%). It is argued that any species of small passerine has the option to use any of the three strategies.