Effects of growth conditions on the activities of superoxide dismutase and NADH-oxidase/NADH-peroxidase inStreptococcus lactis

An increase in the superoxide dismutase (SOD) activity inStreptococcus lactis was observed when the cells were grown at increased oxygen partial pressures or exposed to hyperbaric oxygen tensions. The NADH-oxidase/NADH-peroxidase activities inS. lactis increased in galactose-grown cells when cultivated in air compared with N₂/CO₂. This effect did not occur when glucose was the carbon source; however, an increase in the activities of these enzymes was observed in oxygen atmosphere. The correlation between SOD, NADH-oxidase/NADH-peroxidase, and the metabolic pathways involved is discussed. The effect of manganese on the SOD activity is also considered.     

The transducer and encoder of frog muscle spindles are essentially nonlinear. Physiological conclusions from a white-noise analysis

1. Nonlinear second order white-noise analysis has been applied to the isolated frog muscle spindle. Power (²) of the Gaussian white noise (GWN) and the average prestretch level L were varied and the response of both the isolated receptor potential (transducer) and the action potential (encoder) level were analysed. 2. The standard white-noise method is briefly presented. Particular emphasis, however, is put on the limitations in the range of validity of the method and, consequently, on the use and interpretation of the kernels as a Wiener model. Conclusions in the present paper are within this frame and are mainly of qualitative nature. 3. The analysis reveals that the nonlinear contributions of the model are essential for approximating physiological results, thus ruling out purely linear modelling for this receptor organ. 4. The dependence of the transducer kernels on are compatible with the behaviour of a rectifier. Rectification is represented by the lack of hyperpolarization within the isolated receptor potential and is enhanced by the substantial memory in the linear and nonlinear kernels as demonstrated by their extent in time. This is equivalent to low power in high frequencies of the response. Obviously, the hyperpolarizing potentials following each spike counteract the long transducer memory. 5. At the encoder level the memory of the system is strongly reduced. This is achieved by using predominantly high frequency components of the receptor potential for triggering the process of impulse generation, and by the precise coupling and high frequency content of the impulses. This coupling precision is possible because of the sensitivity of the spike-generating mechanism to steep rising transients of the receptor potential and also owing to the reduction in transducer memory by the hyperpolarizing afferpotentials. 6. The preference given to the high frequency components is also read from the structure of the second order transducer kernel and from both the linear and the second order encoder kernels, which allows the most effective input waveform for triggering action potentials to be determined. 6. When the operating point is changed to higher prestretch values, kernel heights increase strongly implying higher response strength of the muscle spindle. The kernel structure is changed as well in the direction of reducing the effective memory already at the level of the receptor potentials, probably a means to prevent too high depolarization values.     

Optomotor control of the force of flight in Drosophila and Musca

Specialized networks of movement detectors in the antero-inferior field of the eyes of the fruitfly, Drosophila melanogaster, and the housefly, Musca domestica, respond to upward (or downward) drift of the retinal images by excitation (or inhibition) of the lift-generating force of flight. The influence of the direction of pattern movement upon the altitude control response has been investigated under conditions of fixed flight in still air. Matched model analysis of the available response curves suggests the predominance of unidirectional movement detectors in these networks. Homologous wingbeat-inhibiting detectors in the specified fields of the eyes of the two species respond preferentially to pattern movement from antero-superior to postero-inferior. The arrangement of wingbeat-exciting detectors seems to follow different schemes: These detectors respond preferentially to movement from inferior to superior in Drosophila, and to movement from antero-inferior to postero-superior in Musca. The wingbeat-exciting network in Musca is restricted to a comparatively small antero-equatorial area of the specified fields of the eyes. The combination of the two types of detectors in this area establishes a powerful lift control system which is particularly sensitive to minute deviations from a given level of flight.     

Effects of mixed neutron-gamma irradiation in vivo on the cell surfaces of murine blood cells

Summary For studies on cell membranes, mice were exposed to mixed neutron + gamma reactor-radiation in the range of total doses from 0.5 to 4.5 Gy. Changes in functional activity of plasma membranes of erythrocytes, platelets, and lymphocytes were followed by a lectin-binding technique at various intervals afterwards. The amount of³H-concanavalin A bound to cells altered considerably during the 1st h after irradiation in all cell types. Lymphocytes and platelets, however, were more sensitive than erythrocytes as increased lectin-binding could already be observed after 0.5 Gy. The binding ability of these cells performed oscillatory behaviour. In addition, alterations in shapes and ultrastructure of cell surfaces and intracellular membranes were observed.     

Localization of visual pigments within rhabdoms of the compound eye of Spodoptera exempta (Insecta,Noctuidae)

Summary In the noctuid moth Spodoptera exempta, the distribution of visual pigments within the fused rhabdoms of the compound eyes was investigated by electron microscopy. Each ommatidium regularly contains eight receptor cells belonging to three morphological types: one distal, six medial, and one basal cell (Meinecke 1981); four different visual pigments — absorption maxima at approximately 355, 465, 515, and 560 nm — are known to occur within the eye (Langer et al. 1979). The compound eyes were illuminated in situ by use of monochromatic light of different wavelengths. This illumination produced a wide scale of structural changes in the microvilli of the rhabdomeres of individual cells. Preparation of eyes by freeze-substitution revealed the structural changes in the rhabdomeres to be effects of light occurring in vivo.The degree of structural changes may be considerably different in rhabdomeres within the same ommatidium; it was found to depend on the wavelength and the duration of illumination, the intensity received by the ommatidia as well as the spectral sensitivity of the receptor cells. Therefore, it was possible to estimate the spectral sensitivities of the morphological types of receptor cells. Generally, all medial cells are green receptors and all basal cells red receptors; distal cells are blue receptors in about two-thirds of the ommatidia, while in the remaining third of them distal cells are sensitive to ultraviolet light.Supported by Deutsche Forschungsgemeinschaft, Sonderforschungsbereich 114 (Bionach)     

Preparation and discharge of secretion in the subcommissural organ of the rat

Summary The secretion of the subcommissural organ (SCO) of the rat was studied by means of immunocytochemistry at the electron-microscopic level with the use of (1) the polar embedding medium Lowicryl K4M at -30° C, (2) the protein A-gold technique, and (3) a rabbit antiserum against bovine Reissner's fiber (see Sterba et al. 1981).Two different substructures of the ependymal and the hypendymal SCO-cells display a positive immunocytochemical reaction: (1) sacs containing flocculent secretion, which originate from the granular endoplasmic reticulum, and (2) vacuoles filled with fine granular secretion, which are pinched off from the Golgi apparatus. The secretory material of the sacs and the vacuoles is discharged both (i) apically into the cerebrospinal fluid and (ii) basally into intercellular spaces of the SCO-hypendyma. The apically released secretion is condensed to a lamina-like formation, which more caudally assumes the form of Reissner's fiber. The route of the basally released secretion remains, however, vague. The periodically striated bodies, which were thought to be morphological mediators of the discharge of the secretion into the capillaries, are never labeled by gold particles.Supported by grants from the Ministry for Science and Technology of the German Democratic RepublicThe expert technical assistance of Mrs. B. Wolff, Mrs. S. Mehnert, Mrs. E. Siebert, Mrs. Ch. Schneider, and Mrs. I. Seifert is gratefully acknowledged     

Potassium accumulation in growing Methanobacterium thermoautotrophicum and its relation to the electrochemical proton gradient

Cultures of Methanobacterium thermoautotrophicum (Marburg) growing on media low in potassium accumulated the cation up to a maximal concentration gradient ([K⁺]_{intracellular}/[K⁺]_{extracellular}) of approximately 50,000-fold. Under these conditions, the membrane potential was determined by measuring the equilibrium distribution of the lipophilic cation (¹⁴C) tetraphenylphosphonium (TPP⁺). This cation was accumulated by the cells 350-to 1,000-fold corresponding to a membrane potential (inside negative) of 170–200 mV. The pH gradient, as measured by equilibrium distribution of the weak acid, benzoic acid, was found to be lower than 0.1 pH units (extracellular pH=6.8). The addition of valinomycin (0.5–1 nmol/mg cells) to the culture reduced the maximal concentration gradient of potassium from 50,000-to approximately 500-fold, without changing the membrane potential. After dissipation of the membrane potential by the addition of ¹²C-TTP⁺ (2 mol/mg cells) or tetrachlorosalicylanilide (3 nmol/mg cells), a rapid and complete efflux of potassium was observed.These data indicate that potassium accumulation in the absence of valinomycin is not in equilibrium with the membrane potential. It is concluded that at low extracellular K⁺ concentrations potassium is not accumulated by M. thermoautotrophicum via an electrogenic uniport mechanism.Non-common abbreviations TPP⁺ Tetra phenylphosphonium bromide - DTE Dithioerythritol - TCS 3,5,3,4-Tetrachlorosalycylanilide     

Interaction of metabolic inhibitors with actin fibrils

Summary The dependence of the arrangement of fibrillar actin in cultured endothelial cells on metabolic conditions was investigated with cellular elements derived from the heart of Xenopus laevis tadpoles. Either primary culture or an established cell line (XTH-2) were used in these studies The metabolic stage of the cells was influenced by inhibiting respiration and lactate production. The actin pattern was revealed either by indirect immunofluorescence or by tetramethylrhodaminyl (TRITC)-phalloidin fluorescence. Total block of energy supply causes in all cases a distinct loss of actin fibrils, while inhibition of respiration alone increases the variability of actin organization. In primary XTH cells but not in XTH-2 cells cyanide disintegrates most of the actin fibres during 3 h of treatment. This effect is independent of the inhibition of respiration, since actin gels prepared from skeletal muscle also undergo destruction in the presence of cyanide. It is concluded that the actin fibrils of the primary cells and the established line behave differently to changing metabolic conditions and to application of KCN.     

Are the funnel-canal organs the “campaniform sensilla” of the shore crab Carcinus maenas (Crustacea,Decapoda)?

Summary The topography of the funnel-canal organs of Carcinus maenas (Decapoda, Crustacea) and their stimulus-receiving cuticular and sensory apparatus were studied in the light and electron microscopes.About 4000 funnel-canal organs are situated within the exoskeleton of Carcinus. Almost all of them are on the distal segments of the walking legs, in particular on the epicuticular cap at the tip of the dactyl. They were not found to be arranged in groups or sensilla fields, and no sex-specific differences were observed.Characteristic features of the funnel-canal organs are as follows: (a) There is a terminal pore (0.5×0.8 m diameter) in the cuticle, at the tip of a small projection. It is closed by a plug of electron-dense material. (b) The terminal sections of the dendrites are enclosed in a dendritic sheath up to ca. 10 m below the pore. (c) The dendrites, 3–24 in number, end below the plug; none of the dendrites exhibits a tubular body; two of the dendrites are distinguished from the others by the greater number of microtubules in their outer segments.The structural characteristics, in particular the gustatory pore and the number of dendrites, are typical of bimodal receptors in arthropods. In such receptors, as in the contact chemoreceptors of insects and arachnids, mechano-and chemosensitive sensory cells are combined.This interpretation of the function of the funnel-canal organs is supported by electrophysiological data of other authors.The morphological parameters we find for the funnelcanal organs, in comparison with those of insect campaniform sensilla, provide clear evidence against the reclassification of the funnel-canal organs as crustacean campaniform organs proposed by Shelton and Laverack (1968).Supported by the Deutsche Forschungsgemeinschaft (W.G., SFB 45/A1)We thank Professor Dr. F.G. Barth for valuable discussion and Mr. K. Grommet for drawing the Figs. 1 and 6c     

Enkephalin immunoreactivity in iris nerves: Distribution in normal and grafted irides,persistence and enhanced fluorescence after denervations

Summary The morphology and distribution of nerve fibers showing enkephalin-like immunoreactivity was studied in rat and mouse iris whole mounts. In adult rat, a relatively dense network of varicose fibers was seen throughout the iris. Individual, long, usually smooth fibers were observed running together with non-fluorescent fibers in bundles. Positive nerve fibers were also seen in the ciliary body and the choroid membrane. The fluorescence intensity was normally low. No enkephalin-positive fibers were detected in adult mouse iris.Extirpation or lesioning either one or all the three ganglia known to supply the rat iris with nerve fibers, the superior cervical, the ciliary and the trigeminal ganglia, caused no detectable decrease in amount of enkephalin-positive fibers. However, in irides grafted to the anterior eye chamber of adult recipients, no enkephalin-positive fibers could be observed 2–12 days postoperatively, strongly suggesting that degeneration of these fibers had occurred. When iris grafts were left longer in the eye, nerve fibers with enkephalin-like immunoreactivity reappeared. An increased fluorescence intensity was observed both in the ipsilateral and contralateral iris following extirpation or lesioning all three ganglia and in the ipsilateral iris after extirpation of the ciliary ganglion. Three days after a systemic injection of capsaicin, which causes a permanent disappearance of substance P fibers, the same phenomenon was often observed. This raises the possibility of an interaction between the enkephalin-positive and the substance P fiber systems in the iris.The present experiments thus demonstrate a rich network of enkephalin immunoreactive nerve fibers in the rat iris originating outside the iris but apparently not in the ciliary, trigeminal or superior cervical ganglion.