Showing papers by "University of Konstanz published in 1978"

The mosaic of nerve cells in the mammalian retina.

Abstract: Cells from three different layers of the retina were tested for regular horizontal arrangement or random distribution. Monkey cones, cat cones, cat A-type horizontal cells and cat alpha-ganglion cells are all arranged in a regular mosaic. This was assessed by measuring the distance to the nearest neighbour of each cell. The nearest neighbour distributions differed significantly from those of random dot patterns. The precision of the mosaic decreased in the order monkey cones, cat cones, cat A-type horizontal cells, cat alpha-ganglion cells. All four cell types were - independent of density - more regularly arranged in the centre of the retina than in the periphery. The advantages of a regular arrangement compared with a random distribution and mechanisms which could generate a regular mosaic are discussed.

Transport of oppositely charged lipophilic probe ions in lipid bilayer membranes having various structures

Abstract: A comparative study of the charge transport kinetics of oppositely charged lipophilic probe ions in lipid bilayer membranes of varying composition was carried out by using the charge pulse technique. The ions investigated were the chemical analogs tetraphenylborate, tetraphenylarsonium and tetraphenylphosphonium. Membrane structural aspects investigated were the type of solvent used in membrane formation, sterol content, and the nature of the principal lipid. The overall results indicate that the character of the transport process involving positive lipophilic probes is, in contrast to positively charged carrier complexes, very similar to that deduced in previous studies of negative lipophilic ions. The major effect on transport of lipophilic ions of both signs using differentn-alkane solvents appears to be due to changes in the thickness of the membrane hydrocarbon region. Positive ion transport is relatively sensitive to the inclusion of sterols of several types in both monoolein and lecithin membranes, as compared with negative ion transport, suggesting that a combination of sterol-induced dipolar field and fluidity changes are involved. Results involving several variations in lipid structure, with the possible exception of hydrocarbon tail saturation, when interpreted in terms of dipolar field changes deduced under the assumption of charge independent fluidity effects, are consistent with monolayer surface potential measurements.

Recruitment and food-retrieving behavior in Novomessor (Formicidae, Hymenoptera)

Abstract: 1. In this article, we report the communicative effect of stridulation signals in Novomessor cockerelli and N. albisetosus during foraging 2. The structure of the stridulatory organ and the main characteristics of airborne and substrate-borne stridulation signals are described. 3. The stridulation signals are not perceived by the ants over any appreciable distance. However, workers that contact an object transmitting stridulatory vibrations stay at this probe significantly longer than at a nonvibrating control probe. 4. An information transfer analysis was performed by comparing the probabilities of occurrence of different behavioral acts in workers both before and after contacting either a ‘stridulatory’ test probe or a ‘silent’ control probe. Stridulation did not affect the behavior of food carriers; diggers that carried debris from the nest were slightly but significantly influenced; but a remarkable change did occur in the probabilities of behavioral acts by scout ants. 5. Stridulation alone does not release a specific behavioral response but rather enhances more or less a change to different behavioral activities in workers. 6. In a series of field experiments, it was shown that a prey object too large to be retrieved by one ant stimulates the finder ant to stridulate. It was further demonstrated that the vibrational signals received by a second ant that also contacted a prey enhance the release of chemical short-range recruitment signals by this ant. In our experiments, the facilitating effect of stridulation on chemical recruitment led to a time advance of 1–2 min in both the recruitment of workers and in the retrieval of large prey objects by groups of foragers. It has been demonstrated that the rapid group retrieval of large prey objects enables Novomessor workers to successfully compete with mass-recruiting ant species such as Solenopsis and Iridomyrmex. 7. Significantly more digging is only released at a ‘stridulatory’ test probe if the probe is offered very close to a nest entrance. 8. Stridulation in ants seems to be a mechanism for modulating the state of readiness of receivers to react to other stimuli (modulatory communication). The stridulation signal adjusts the distribution of the worker force to a given situation and to group needs in a graded fashion, but does not by itself release specific behavioral reactions. This phenomenon is compared with similar functions in other communication systems of complex animal societies.

Topography of horizontal cells in the retina of the domestic cat

Abstract: Neurofibrillar methods stain a class of horizontal cells in the cat retina which are shown to be identical with the A-type horizontal cell of Golgi-staining. Thus all of the A-type cells of a single retina can be observed. On this basis the changes in density and dendritic field size of A-type horizontal cells with respect to retinal eccentricity were measured. The decrease in density from centre to periphery is balanced by a corresponding increase in size of the dendritic field. Consequently each retinal point-independent of retinal position - is covered by the dendritic fields of three or four A-type horizontal cells. The nuclei and nucleoli of B-type horizontal cells could also be recognized in neurofibrillar-stained material and thus their distribution was determined. The density ratio B-type: A-type is 2.8 $\pm $ 0.4 and does not vary much from the centre to the periphery of the retina. Each retinal point is also covered by four B-type horizontal cells. Thus a single cone can contact a maximum of eight horizontal cells. The rate of density decrease from centre to periphery is closely similar in cones and horizontal cells but greater in ganglion cells.

Caterpillars detect flying wasps by hairs sensitive to airborne vibration

Abstract: 1. Intact caterpillars (Barathra brassicae) react to the airborne vibrations of an approaching wasp (Dolichovespula media) by cessation of movement or by squirming. These reactions are no longer observed after removal of the eight filiform hairs on the caterpillars' thorax. When directly attacked, both intact and operated caterpillars squirm and often regurgitate gut-contents. 2. The selective advantage of detecting a wasp's approach with the vibration sensitive hairs was quantitatively determined. A cage contained a wasp colony and intact or operated caterpillars as the only prey: it was found that intact caterpillars which react to the wasp's approach are attacked about 30% less frequently than operated animals. Of all caterpillars that are attacked, about 20% are killed. Of all caterpillars killed 30% were intact, while 70% lacked their filiform hairs (P<0.001). 3. Air vibration generated in the near field of a tethered wasp in flight was measured at different distances and directions. The dominant frequency in the spectral energy distribution of flight-generated vibration was about 150 Hz. Maximal medium displacements were below and behind the wasp (Figs. 2 and 3). This vibration amplitude was above threshold for the filiform hairs (at 150 Hz) up to a distance of 70 cm from the wasp. 4. The influence of the caterpillars' response on the hunting strategies of wasps predating or parasitizing on them is discussed.

Analysis of the multi-pore system of alamethicin in a lipid membrane

Abstract: The electrical properties of an alamethicin multi-pore system have been studied by voltage-jump current-relaxation experiments (this paper) and by autocorrelation and spectral analysis (following paper). With these methods a slow time constant and a fast time constant were observed which differ by about one to three orders of magnitude depending on the experimental conditions. Steady-state current and time constants were analyzed as functions of voltage, alamethicin concentration and temperature. Within experimental error the data obtained with these different methods are in good agreement. The experimentally measured relation between the voltage and alamethicin concentration dependence of the slow relaxation time fits into a model of an alamethicin pore which adopts consecutive pore states and which decays only from the lowest state. It indicates that the uptake of one alamethicin molecule by the existing pore and, in formal equivalence, the transfer of about one positive elementary charge across the membrane are associated with the transition from a given pore conductance state to the next higher state. From the voltage and alamethicin concentration dependence of the pore formation rate evidence shows that a hexameric preaggregate exists at the membrane interface out of which two to three molecules are simultaneously inserted into the membrane to form the pore nucleus. The effects of different voltage pretreatment on the experimentally determined parameters have been investigated and are discussed in detail.

Membranes rich in acetylcholine receptor: characterization and reconstitution to excitable membranes from exogenous lipids.

Abstract: Characterization of acetylcholine-receptor-enriched membranes from Torpedo californica electric tissue by negative-staining electron-microscopy and by lipid analysis is described. The protein/lipid ratio is 70%/30%. The lipids consist of 70% phospholipids (46% phosphatidylcholine, 31% phosphatidylethanolamine, 14% phosphatidylserine, 7% sphingomyelin, 2% phosphatidylinositol of the phospholipids determined) and 20% cholesterol. The acetylcholinesterase-enriched membranes show a similar composition. The only differences are a lower protein/lipid ratio (45%/55%) and a lower phosphatidylcholine/sphingomyelin ratio of 39%/14% as compared to 46%/7% for the receptor-enriched membranes. A method of preparing single-walled phosphatidylcholine vesicles by gel filtration on Sephadex G50 according to Brunner et al. (Biochem. Biophys. Acta, 455, 322--331, 1976) is used to recombine the lipid-depleted receptor complex with artificial lipid vesicles. Starting from a lipid mixture of 46% phosphatidylcholine, 31% phosphatidylethanolamine, 14% phosphatidylserine, 7% sphingomyelin, 2% phosphatidylinositol and 15% cholesterol we obtained vesicles associated with the acetylcholine receptor complex. These receptor vesicles are chemically excitable by 10 micrometer carbamoylcholine as measured by efflux of 22Na+ from the vesicles. The excitability is blocked by preincubation with 0.5 mM alpha-toxin from Naja naja siamensis venom and by reduction with 5 mM dithioerythritol.

Recruitment and food-retrieving behavior in Novomessor (Formicidae, Hymenoptera) - I. Chemical signals

Abstract: 1. Novomessor cockerelli and N. albisetosus have been considered by previous authors to be individual foragers. This investigation, however, has demonstrated that workers of both species employ recruitment techniques when they encounter large prey. 2. Novomessor workers usually carry large food items in a cooperative action directly to the nest. 3. The chemical communication system employed during foraging was investigated in laboratory and field experiments. Secretions released from the poison gland proved to be the most effective recruitment signal. 4. In order to summon nestmates to large food objects, Novomessor employs the following two different recruitment techniques. Short-range recruitment: After discovering the prey, the scout releases poison gland secretion into the air. Nestmates already in the vicinity are attracted from as far away as 2 m and move upwind toward the prey. Long-range recruitment: If short-range recruitment does not attract enough foragers, a scout lays a chemical trail with poison gland secretion from the prey to the nest. Nestmates are stimulated by the pheromone alone to leave the nest and follow the trail toward the prey. 5. The trail pheromone is short-lived, and trail laying consequently does not lead to mass communication. Instead, the pheromone releases a short pulse of outrushing ants, usually numerous enough to subdue the prey and to carry it home when the ants act jointly. 6. In several field experiments, we demonstrated that these recruitment and prey-retrieving techniques enable Novomessor to counteract interference competition by mass-recruiting ant species.

Bilayer Lipid Membranes

Abstract: Thin lipid membranes formed across an aperture in a teflon foil are frequently used as model systems to simulate the hydrophobic diffusion barrier of biological membranes. These membranes have a thickness of about twice the length of a lipid molecule (bilayer membranes) and are prepared either by a spontaneous transition of a thick lamella made from a solution of lipids in a hydrocarbon [1] or by a direct “addition” of two monomolecular lipid layers on the two water surfaces separated by the teflon foil [2]. The aqueous phases on both sides of these planar membranes are easily accessible by electrodes which may serve to study the electrical properties of the membranes. The whole system allows the application of steady state electrical methods as well as that of fast relaxation methods. The latter include the voltage jump-current relaxation technique [3,6], the charge pulse method [4,5] as well as the temperature jump method [6]. These kinetic techniques have been used throughout recent years to investigate ion transport phenomena across bilayer lipid membranes. Unmodified lipid membranes have been found to represent high energy barriers for the movement of inorganic cations and anions. A simple equivalent electrical circuit of the membrane consists of a parallel arrangement of the membrane resistance RM and the membrane capacitance CM (typical values: RM = 106-108μcm2, CM = 0.3-0.8μF/cm2). A refined version composed of three of such elements (one for the hydrocarbonlike membrane interior, the two others for the polar membrane-water interfaces) has been suggested on the basis of a.c. measurements [7]. These measurements were, however, confined to the rather small band width of 0.1-100 Hz. A different possibility of testing such a circuit is to make use of the voltage jump method. The induced current relaxation may be measured with a time resolution of at least 1 μs and very high sensitivity by using signal averaging techniques. For the three element circuit described above the relaxation should consist of two exponential terms. At least five different relaxation times were, however, necessary to obtain a sufficiently good fit to the experimental data [8.9]. This finding indicates that even the refined equivalent circuit is insufficient for a phenomenological description of the high frequency behaviour of bilayer lipid membranes. The complex current relaxation may be interpreted on the basis of cooperative dielectric relaxation phenomena associated with the dipoles of the polar head groups of the lipid molecules.

Effects of certainty, modality shift and guess outcome on evoked potentials and reaction times in chronic schizophrenics

Abstract: Evoked potentials and reaction times were obtained from chronic schizophrenics and normal controls to light and sound stimuli presented in random order. In the ‘ certain’ condition subjects were told what the next stimulus would be, in the ‘uncertain’ condition they were asked to guess. Amplitudes were usually larger for normals than for schizophrenics, for ‘uncertain’ than for ‘certain’ conditions, and in cross- than in ipsimodal stimulus-sequences. The effect of certainty was stronger in normals across 4 leads; so was the effect of modality shift at vertex. While these findings replicate earlier results from acute schizophrenics, no condition x group interactions could be found in the reaction time measures.Two additional results were interpreted as showing basically different attitudes with respect to the predictability of events: (1) there was a slow positivity between the verbal information and the following stimuli which was largest for schizophrenics in the conditions of certainty; (2) while normals showed long-term habituation only in N1- but not in P3-amplitudes, the reverse was true for schizophrenics.

Malignant hyperphenylalaninaemia--current status (June 1977).

Abstract: D. M. DANKS (Royal Children's Hospital, Parkville, 3052, ifielbourne, Australia) K. BARTItOLOMg (Kinderklinik der Universitdt, 6900 Heidelberg 1, tt~meislerweg 1-9, West Germany) B. E. CLAYTON (Department of Chemical Pathology,, Hospital for Sick Children, Great Ormond Street, London) H. Cua'nus (Biochemistry Department, Kinderspital, Zurich, Swilzerland) H. GR/SBt,: (Children's Hospital , Universily of Miinster, Munster, West Germany) S. KAUFMAN (Laboratory of Neurochemistry, Nationa! Institute of 3/ienta! Health, Bethesda, Maryland 20014, USA) R. LEEMn~O (Microbiology Department, The General Hospital, Steelhouse Lane, Birmingham, UK) W. PFLEIDERER (Fachbereich Chemic, Universito't Konstanz, Constance, West Germany) H. REMBOLD ( Max-Planc/~ Institut fiir Biochemie, Martinsvied bei Miinchen, Munich, West Germany) F. RE,z (ttopitat des Enfants Malades, ]47 Rue de Sevres, Paris, France)

Segmental and interganglionic projections from primary fibres of insect mechanoreceptors.

Abstract: Projections of primary insect mechanoreceptor fibres in Locusta migratoria and Acheta domesticus are visualised with the cobalt intensification technique after axonal or dendritic filling with cobaltous chloride. Chordotonal proprioceptors of the locust mesothoracic thoracocoxal joint have typical segmental projections and more or less widespread interganglionic processes into the metathoracic, prothoracic and even suboesophageal ganglia. Similar observations can be made on locust abdominal chordotonal organs, from some of which all primary axons project into five preceding neuromeres or ganglia. From locust abdominal stretch receptors and cricket mechanosensitive sternal hairs single afferent axons extend through several ganglia. Locust campaniform sensilla and clavate hair projections of crickets terminate locally. It is concluded that many interganglionic primary afferents contribute to intersegmental control of motor coordination in insects.

Solar cell materials and their basic parameters

Abstract: Parameters such as the energy gapE g , open circuit voltageV oc , short circuit current densityj sc , fill factor F.F., efficiency η, antireflection coating condition A.R. and illumination conditions of currently known photovoltaic diodes are reviewed and tabulated, followed by some critical comments.

The acetylcholine receptor as part of a protein complex in receptor-enriched membrane fragments from Torpedo californica electric tissue.

Abstract: The acetylcholine receptor from Torpedo californica electric tissue consisting of polypeptide chains of molecular weight 42000 (+/- 2000) is part of a protein complex. Cross-linking experiments with bifunctional reagents have shown that this complex has possibly a pentameric structure with a molecular weight of 270000 (+/- 30000). Besides the receptor subunit (alpha-chain), at least three further classes of polypeptide chains are part of the complex: beta (Mr 48000), gamma (Mr 62000) and delta (Mr 68000). This can be shown by cross-linking the proteins extracted from receptor-enriched membrane fractions with a cleavable reagent: From the 270000 molecular weight particle the four predominant polypeptide chains of the membrane, alpha, beta, gamma, and delta, can be obtained. The gamma-polypeptide chains appear to form a dimer connected by an inter-chain disulphide bridge.

The prefrontal cortex of the cat: anatomical subdivisions based on retrograde labeling of cells in the mediodorsal thalamic nucleus.

Abstract: Different areas of the frontal cortex of the cat were injected with small amounts of horseradish peroxidase. The region of labeled cells in the mediodorsal nucleus of the thalamus (MD) were related to the injected areas. Distinct relations between subdivisions of MD and of the prefrontal cortex were established: a rather large central sector of MD projects to the gyrus proreus and the anterior parts of the gyri sigmoideus, rectus, and frontalis. A narrow lateral band of anterior MD neurons projects predominantly to an area on both sides of the sulcus praesylvius, whereas a postero-lateral band sends fibers to a region on the ventral anterior sylvian gyrus. The area between the presylvian sulcus and the sylvian gyrus is apparently free of MD afferents, but not of other thalamic afferents. A fourth sector of MD, situated dorsomedially, projects to the middle parts of the gyri rectus and frontalis. And a fifth sector, located ventrally to the dorsomedial MD sector, projects to the ventral part of the gyrus rectus. The established subfields of MD and of the prefrontal cortex are discussed with respect to previous anatomical research in the cat.

Quantitative determination of ferredoxin, ferredoxin-NADP+ reductase and plastocyanin in spinach chloroplasts.

Abstract: Ferredoxin, ferredoxin-NADP+ reductase and plastocyanin extracted from spinach chloroplasts were determined by quantitative immunoelectrophoresis in an antiserum-containing gel. The advantage of the method is its high sensitivity and specificity so that crude extracts can be directly analysed. It requires, however, purified electron carriers and the corresponding monospecific antibodies. The ratios of ferredoxin to reductase to plastocyanin approximated 5: 3: 4, respectively, per cytochrome f or P700 in spinach chloroplasts.

Alkali ion transport through lipid bilayer membranes mediated by enniatin A and B and beauvericin.

Abstract: Stationary conductance measurements with lipid bilayer membranes in the presence of enniatin A and B and beauvericin were performed. For comparison, some valinomycin systems were investigated. It was found that the conductance in the case of enniatin A and B is caused by a carrier ion complex with a 1∶1 stoichiometry, whereas for beauvericin, a 3∶1 carrier ion complex has to be assumed to explain the dependence of the conductance on carrier and ion concentration in the aqueous phase. The current-voltage curves measured with dioleoyl phosphatidylcholine membranes show a superlinear behavior for the three carriers in the presence of potassium. On the other hand, supralinear current-voltage curves were observed with membranes from different monoglycerides, except for beauvericin. The results obtained with enniatin A and B are in a satisfactory agreement with an earlier proposed carrier model assuming a complexation between carrier and ion at the membrane water interface. The discrimination between potassium and sodium ions is much smaller for the enniatins than for valinomycin. This smaller selectivity as well as the fact that potassium ions cause the highest conductance with lipid bilayer membranes may be due to the smaller size of the cyclic enniatin molecules, which contain 6 residues in the ringvs. 12 in the case of valinomycin. Charge-pulse relaxation studies were performed with enniatin A and B, beauvericin, and valinomycin. For monoolein membranes only in the case of valinomycin, all three relaxations predicted by the model could be resolved. In the case of the probably more fluid membranes from monolinolein (Δ9, 12-C18: 2) and monolinolenin (Δ9, 12, 15-C18: 3) for all carrier systems except for beauvericin, three relaxations were observed. The association rate constantk R , the dissociation rate constantk D , and the two translocation rate constantsk MS andk s for complexed and free carrier, respectively, could be calculated from the relaxation data. The carrier concentration in the aqueous phase had no influence on the rate constants in all cases, whereas a strong saturation of the association rate constantk R with increasing ion concentration was found for the enniatins. Because of the saturation,k R did not exceed a value of 4×105 m −1 sec−1 with 1m salt irrespective of carrier, ion, or membrane-forming lipid. A similar but less pronounced saturation behavior was also observed for the translocation rate constantk S of the free carrier. The other two rate constants were independent of the ion concentration in the aqueous phase. In the case of the enniatins, the translocation rate constantk MS was not independent from the kind of the transported ion. In the series K+, Rb+ and Cs+,k MS increases about threefold. The turnover numbers for the carriers as calculated from the rate constants range between 104 sec−1 and 105 sec−1 and do not show a strong difference between the individual carriers. The conductance difference in the systems investigated here is therefore mainly caused by the partition coefficients, which are smaller for the enniatins than for valinomycin.

Pole cap formation in Escherichia coli following induction of the maltose-binding protein.

Abstract: After induction with maltose, 30--40% of the total protein in the osmotic shock fluid consist of maltose-binding protein while the induction ratio (maltose versus glycerol grown cells) for the amount of binding protein synthesized as well as for maltose transport is in the order of 10. Induction of maltose transport does not occur during all times of the cell cycle, but only shortly before cell division. Electronmicroscopic analysis of cells grown logarithmically on glycerol or maltose revealed in the latter the formation of large pole caps. These pole caps arise from an enlargement of the periplasmic space. Small cells contain one pole cap, large cells contain two. Pulse label studies with strain BUG-6, a mutant that is temperature sensitive for cell division reveal the following: Growth at the non-permissive temperature prevents maltose-binding protein synthesis and formation of new transport capacity. After shifting to the permissive temperature the cells regain both functions. Simultaneously, the newly formed cells exhibit pole caps. We conclude that the induction of maltose-binding protein is responsible for the formation of pole caps. In addition, beside the presence of inducer, cell cycle events occuring during division are necessary for the synthesis of maltose-binding protein.

Riboflavin Binding in Egg‐White Flavoprotein: the Role of Tryptophan and Tyrosine

Abstract: In egg-white apoflavoprotein six of the nine tyrosines and three of the nine tryptophans have been shown to be accessible to ethylene glycol using solvent perturbation difference spectroscopy. For egg-yolk flavoprotein the same ratio of exposed tyrosines to tryptophans was found, but the native protein structure proved to be more stable against denaturation by solvent. A single tryptophan and a single tyrosine have been demonstrated to be essential for binding of riboflavin by a combination of chemical modification and affinity chromatography techniques. Two of the exposed tyrosines and two of the exposed tryptophans could be modified without loss of binding capacity. Only the essential tyrosine was found to be protected by bound riboflavin against nitration with tetranitromethane, whereas the essential tryptophan was found not to be protected against alkylation by dimethyl-(2-hydroxy-5-nitrobenzyl)-sulfonium bromide. Indocyanine green, a hydrophobic probe, binds to egg-white flavoprotein, with a Kd of 10−6 M, most probably at the cofactor binding site. An intramolecular dihydroflavin · nicotinamide complex is bound to the apoprotein (Kd∼ 10−4 M) in a geometry still allowing charge transfer interaction between dihydro-flavin and nicotinamide. These data lead us to propose that egg-white flavoprotein binds riboflavin at a hydrophobic site near to or at the suface of the protein. Tyrosine is probably involved in a stacking interaction with riboflavin and tryptophan is also essential for binding. The dimethylbenzene part of the flavin nucleus appears to be buried in egg-white flavoprotein in contrast to flavodoxins where it has been shown to be exposed.

Structure of the oxygen adduct intermediate in the bacterial luciferase reaction: 13C nuclear magnetic resonance determination

Abstract: By using FMN enriched in 13C (90%) at position C-4a, we have conclusively shown that the reaction of molecular oxygen with bacterial luciferase-bound FMNH2 forms an adduct at the 4a position. Consistent with this are 13C NMR studies of FMN and other flavin compounds which show that this carbon should be unusually reactive in the reduced 1,5-dihydroflavins with respect to electrophilic attacks.