Fast and slow photoreceptors — a comparative study of the functional diversity of coding and conductances in the Diptera

1. From a comparison of the photoresponses and membrane properties of photoreceptors from 20 species of Diptera, we conclude that coding in the time domain is matched to the dictates of visual ecology. This matching involves the dynamics of phototransduction and the use of an appropriate mix of potassium conductances to tune the photoreceptor membrane.
2. Rapidly flying, manoeuvrable diurnal Diptera from several families have fast photoreceptors, with corner frequencies (the frequency at which signal power falls by a half) of between 50 and 107 Hz. The ponderous and predominantly nocturnal tipulids have slow photoreceptors with fully light adapted corner frequencies of 16 to 19 Hz.
3. Dark adapted fast photoreceptors have a lower gain (as indicated by lower noise levels), a lower sensitivity, and light adapt more rapidly than dark adapted slow photoreceptors. Fast cells also have much lower input resistances and shorter time constants.
4. Fast photoreceptors rectify more strongly in the steady state because of a weakly inactivating delayed rectifier potassium conductance with fast and slow components of activation. Slow photoreceptors rectify less strongly in the steady state because their membrane properties are dominated by strongly inactivating outward currents with reversal potentials in the range — 80 to -90 mV.
5. The differences between potassium conductances match the differing functional requirements of fast and slow photoreceptors. The non-inactivating delayed rectifier promotes the rapid response of fast cells by reducing the membrane time constant. This is an expensive strategy, involving large conductances and currents. Slowly flying nocturnal insects do not require a high speed of response. The potassium conductances in their slow photoreceptors inactivate to avoid costly and unnecessary ion fluxes.
6. Both the dynamics of the photoresponse and photoreceptor membrane properties exhibit sexual dimorphism. Light adapted photoreceptors in the enlarged male dorsal eye of Bibio markii have a corner frequency of 42 Hz, compared with 27 Hz for cells in the smaller female eye. This difference in frequency response correlates with the male's higher spatial acuity and is accompanied by consistent differences in potassium conductance activation rate. We conclude that the divison between fast and slow cells is the product of cellular constraints, metabolic costs and the requirements of coding efficiency at different light levels and retinal image velocities.

     

Improvements of the membrane filter method for DNA:rRNA hybridization

We describe and recommend the following improvements of DNA:rRNA membrane filter hybridization methods. One of our aims was to avoid DNA release from filter discs during hybridization.

1. Our hybridization conditions are 2 SSC in aq. dest., with 20% formamide, 50 C, overnight for 16 hr.
2. Duplexing is over in 8–10 hr.
3. Formamide has to be very pure (O.D.≤0.2/cm light path at 270 nm).
4. RNAase treatment: 250 μg/5 ml 2 SSC/filter at 37 C for 1 hr.
5. Our conditions for stepwise thermal denaturation are: 5°C steps from 50C to 90C in 1.5 SSC in 20% formamide.
6. Single-stranded DNA, fixed on membrane filters, and stored in vacuo at 4C, can be used reliably for hybridization for up to 20 months.
7. Concentrated DNA in 0.1 SSC, quick-frozen at ?50 C and stored at ?90 C for up to 2 years can be used for hybridization without much change.
8. A CsCl gradient purification step yields much purer DNA, but increases the release of DNA from filters by about 20%. Filters with 20% more DNA is a compensation.
9. rRNA can be stored for 20 months in SSC or 2 SSC at ?12C without changing the hybridization results.

     

Microbial assimilation of hydrocarbons

1. The fine-structure analysis of the hydrocarbon oxidizing microorganism, Acinetobacter sp., demonstrated a cytoplasmic modification resulting from growth on paraffinic and olefinic hydrocarbons.
2. Intracytoplasmic hydrocarbon inclusions were documented by electron microscopy with chemical identifications obtained by gas chromatography and X-ray diffraction.
3. These results demonstrate the ability of a micro-organism to accumulate hydrocarbon substrates intracellularly which, in turn, indicates transport across the cell membrane.

     

A study on the rate of water transport of the clam katelysia opima in relation to environmental conditions

1. The neutral red technique was employed to study the rate of filtration in Katelysia opima.
2. The weight specific water filtration was found to be greater for younger clams compared to the older ones.
3. The rate of water filtration increased with decreasing salinity.
4. Water filtration was found to increase as temperature increased, reaching a maximum at 35°C. but then sharply decreasing at 39°C.
5. Light had no significant effect on the rate of filtration.
6. Suspended matter was found to affect the rate of water filtration.
7. The rate of filtration was low at high pH and high in low pH.
8. The rate of water filtration was found to be faster during high tide than during low tide.
9. The presence of the parasitic crab, Pennotheris sp., in the mantle cavity of clams had a marked effect on the particle filtration.
10. Accidental cut of the siphon tips had no effect on the rate of filtration.

     

Inhibition of carotenoid synthesis in Myxococcus fulvus (Myxobacterales)

1. The inhibitory effects of CPTA, nicotine, DPA, and San 6706 on carotenogenesis in Myxococcus fulvus were investigated.
2. The effects of CPTA, D-nicotine, and L-nicotine were very similar. The action of the drugs wasadditive. The cyclization was inhibited at low doses, the introduction of the hydroxyl group at C-1′ at higher doses. Lycopene accumulated at high drug concentration. The mode of action of the inhibitors is discussed.
3. In a carotenoid mutant of M. fulvus a stimulation of the “7,8-dehydrogenase” by CPTA was observed.
4. The specific carotenoid content of bacteria was increased by DPA due to an enhanced formation of phytoene. At low doses of DPA small amounts of an intermediate carotenoid glucoside ester, a 7,8-dihydro derivative, were detected.
5. DPA was taken up by the plasma membrane. Quantitative removal of DPA by washing was not possible.
6. San 6706 specifically and reversibly blocked the desaturation of phytoene.

     

Acid-base titration across the plasma membrane ofMicrococcus denitrificans: Factors affecting the effective proton conductance and the respiratory rate

The object of this work was to measure the effective proton conductance of the plasma membrane ofMicrococcus denitrificans under various conditions and to investigate possible connections between respiration and proton translocation.

1. Pulsed acid-base titrations of suspensions ofM. denitrificans in a medium containing the permeant thiocyanate ion, or when K⁺ ion permeability was induced by valinomycin in a KCl medium, showed that the normal effective proton conductance of the membrane system was less than 1 μmho/cm².
2. A pH-overshoot artefact was suppressed by adding carbonic anhydrase.
3. The effective proton conductance was increased by the uncoupler FCCP in the same concentration range as was required to stimulate respiration. Concentrations of FCCP above 1·5 μM inhibited respiration after an initial stimulation.
4. The effective proton conductance in presence of 2 μM FCCP was at least 17 μmho/cm².
5. The quantitative relationships between the respiratory rate, the stoichiometry of respiration-driven proton translocation, and the effective proton conductance of the membrane of the cells are compatible with the suggestion that stimulation of respiration by FCCP is due to a release of back-pressure exerted by a protonmotive potential on the respiratory chain system in the membrane. Only one amongst other possible explanations of the stimulation of respiration by FCCP is, however, excluded.

     

Fixation of the plasma membrane/cytoplasm complex: A mechanism of toxic interaction of tributyltin with the cell

Flow cytometric and light/fluorescence microscopic analysis of murine erythroleukemic cells (MELC) and electron microscopic investigation of porcine microsomal membrane preparations suggest that tributyltin (TBT) toxicity is mediated through fixation processes (protein denaturation, crosslinking, and so on) within the plasma membrane/cytoplasm complex. This hypothesis was derived from the following observations:

1. Exposure of the MELC to micromolar concentrations of TBT results in increased resistance to detergent-mediated cytolysis;
2. Exposure of porcine renal microsomal membrane preparations to similar concentrations results in inhibition of vanadate-mediated crystallization of Na⁺,K⁺-ATPase, a process requiring protein mobility within the membrane;
3. Flow cytometric and fluorescence microscopic analyses indicate that MELC exposed to submicromolar concentrations of TBT exhibit increased cellular carboxyfluorescein retention; and
4. Nuclei prepared from TBT-treated cells by detergent-mediated cytolysis exhibit increased axial light loss, 90° light scatter, fluorescein isothiocyanate fluorescence, and the presence of adherent protein-aceous tags. The DNA distribution histogram of such nuclei also is perturbed.

     

The use of toxicokinetics for the safety assessment of drugs acting in the brain

Pharmacological and toxicological studies undertaken on drugs that affect the brain are frequently performed in disparate species under various experimental conditions, at doses often greatly in excess of those expected to be administered to humans, and the findings are extrapolated implicitly or explicitly with scant regard to differences in the biodisposition of the drugs. Such considerations are necessary since:

1. Species;
2. Strain;
3. Gender;
4. Route;
5. Dose;
6. Frequency and time of administration;
7. Temperature;
8. Coadministration of drugs; and
9. Surgical manipulation

are but some of the factors that have been shown to influence the kinetics and metabolism of drugs. This article, using MDMA and other phenylethylamines as examples, provides evidence for the need to measure the exoosure of the drugs and their active metabolites in blood and brain (toxicokinetics) in order that conclusions based only on dynamic, biochemical, or histological evidence are more pertinent. Further, the combined use of toxicokinetic-dynamic modeling can lead to a better appreciation of the mechanisms involved and a more useful approach to the calculation of safety margins.     

Experimental problems using electronic particle counters

The following scheme lists the problems which have been and will continue to be encountered in grazing experiments on natural particle assemblages. In some cases there are solutions, but many of the problems listed below remain intractable. To solve them will require innovative approaches, most probably combining the use of particle counters with other techniques to approach the problem to be solved from several angles at once. Variance between samples due to

- statistical causes (especially caused by large particles) and

- differences between experimental bottles and between experimentals and controls at start of experiment. Shifts in particle distribution during experiment due to

- increase in small particles

- growth of bacteria and other organisms due to excretion of grazers and

- breakage during handling by grazers into fragments. Processes, independent of grazing, leading to changes in particle size distribution due to

- primary production

- grazing by additional components and

- bacterial growth on detrital particles and the formation of detrital flocs.

     

Effet des androgènes sur l’activité sportive

Androgenic hormones seem to be of beneficial effects on sports performance:

- they increase motivation, will, aggressiveness, resistance to the stress and to the fatigue, leading to an increase of the training quantity,

- they increase bone mineralization and probably mechanical resistance,

- they stimulate the bone marrow and so, with the erythropoietin, the erythropoiesis,

- they increase the tendancy to hyperglycemia, but with a decrease of the tolerance to the glucose,

- they stimulate the fatty acids mobilization from the adipose tissue, for their utilization in the muscle during the exercise,

- they participate, for the trained sportmen, to a better gestion of the muscle glycogen storage: their utilization during exercise is decreased,

- they increase the lean body mass, with an increase of the protein synthesis and a decrease of the protein catabolism, leading also to an increase of the muscle force under training. There is no beneficial effect upon the tendons,

- they have an immunomodulation action.

     

The use of a continuous assay system to show the stimulation of phosphoenolpyruvate production in intact mitochondria by valinomycin and by Mn2+

1. A method for the direct recording of the PEP efflux from isolated mitochondria is described.
2. This method has been used to show the stimulation of PEP efflux by externally added Mn⁺⁺ ions.
3. Valinomycin, uncoupler and oleate were also shown to stimulate PEP efflux.
4. Valinomycin caused an increase in the internal concentration of both PEP and citrate.
5. The results indicate that the major pathway of PEP synthesis in isolated mitochondria is via PEP carboxykinase and the results do not call for an unknown pathway of metabolism.
6. Two interactions between PEP and citrate are described; competition for the mitochondrial interior and the stimulation of PEP production by citrate.

     

Glycolipids and the structure of chlorosomes in green bacteria

1. The cellular content of galactolipids in Chlorobium and Chloroflexus is not related to bacteriochlorophyll content nor to the total amount of chlorosome material in the cells.
2. Chlorosomes of both bacteria were agglutinated by Ricinus lectin and the agglutination was increased after treatment of the chlorosomes with trypsin.
3. When cell free preparations of both bacteria were treated with trypsin prior to centrifugation on sucrose gradients, the resulting chlorosome fractions were less contaminated with material derived from the cytoplasmic membrane than when trypsin was not employed.

     

Dual role for extracellular calcium in blowfly phototransduction

1. The effect of inhibiting Ca²⁺-entry during phototransduction in the compound eye of Calliphora vicina has been investigated in a newly developed semiintact preparation. Simultaneous measurements were made of the receptor potential and the light-induced mitochondrial activation while changing the composition of the extracellular fluid.
2. Lowering the extracellular calcium concentration with EGTA: (i) slows down the kinetics of excitation until the peak of the receptor potential is completely suppressed; and (ii) induces a collapse of the plateau phase after 1 s, although illumination continues. Both effects are reversible.
3. Superfusing the preparation with Ringer solution containing the Ca²⁺-antagonist Co²⁺ initially only affects the peak. Prolonged superfusion with Co²⁺ reduces both the peak and the plateau phase. The latter effect of Co²⁺ is similar to introduction of Co²⁺ into the cell via the recording pipette, suggesting that these effects are due to Co²⁺-entry. These effects of Co²⁺ are irreversible.
4. The results with EGTA and Co²⁺ are compared with the reported effect of the Ca²⁺-antagonist La²⁺, which induces a collapse of the plateau phase while leaving the peak relatively unaffected. It is suggested that two [Ca²⁺]_e-dependent processes contribute to blowfly phototransduction. Both processes are sensitive to EGTA, whereas Co²⁺ affects only one and La²⁺ the other.
5. In the presence of EGTA or Co²⁺ the light-induced mitochondrial activation was inhibited. This result supports the hypothesis that upon illumination a rise in the intracellular calcium concentration activates mitochondrial respiration.

     

Seasonal variation in the biochemical composition of Mytilus viridis at Ratnagiri on the West Coast of India

1. The seasonal variation in the water, protein, fat and glycogen contents of the mussel, Mytilus viridis has been studied for the year March, 1974 to March, 1975.
2. The water level increased during the monsoon season and decreased in summer.
3. The level of protein, fat and glycogen showed correlation with the reproductive cycle of the mussel.
4. The protein level was high when the mussels were mature and dropped during the breeding period.
5. During sex change from male to female in May the protein level remained high whereas during sex change from female to male in October and November it was low.
6. The fat level was high in mature mussels and declined on spawning.
7. The glycogen level was at its peak in immature mussels and low in mature.

     

LCA in decision-making processes

Synthetic sulfuric acid is used in a wide range of applications in fine chemical industry. Despite an already performed optimization of input amounts, used sulfuric acid is still a quantitatively important waste by-product. As a result, different utilization technologies for used sulfuric acid exist:

1. production of gypsum
2. thermal reductive cracking
3. thermal cracking and oxidation

This makes an LCA study of this waste by-product quite interesting. In this paper:

? the starting point for a comparative LCA of the above mentioned utilization technologies at a concrete situation is explained, in a work of Ciba-Geigy Corp.

? a short summary of the comparative LCA is presented

? lessons learned from performing the LCA and using it in a decision process are described.

     

The chemical identification of root promoters extracted from avocado tissues

From the Avocado Rooting Promoter (ARP) 4 compounds were isolated and identified as:

1. 1 acetoxy - 2,4 dihydroxy-n-heptadeca-16-en;
2. 1 acetoxy - 2,4 dihydroxy-n-heptadeca-16-yn;
3. 1,2,4 trihydroxy-n-heptadeca-16-en;
4. 1,2,4 trihydroxy-n-heptadeca-16-yn.

The rooting activity of the pure compounds was verified using the mung bean rooting bioassay. Compound 2II is the most active.     

Maladie de La Peyronie: Bilan IRM chez 28 patients

Purpose

to determine diagnosis and prognosis value of MRI in Peyronie’s disease.

Material and Methods

thirty one penile MR examinations have been performed in 28 patients aged between 21 and 73. (1 tesla; surface coil; sagittal SET1, axial SET2 weighted, T1 before and after Gadolinium)

- In all cases but one, fibrous plaques were clinically palpable.

- Images were compared with clinical examination and evolution under anti-inflammatory drugs.

Results

- In 3 cases, MRI misdiagnosed one unique plague.

- In 2 additional cases, one of the 2 clinical plaques was not detected.

- In 5 cases, MRI depicted more lesions than palpation.

- Gadolinium Enhancement was always correlated with a good response to anti-inflamatory drugs but this treatment was also useful in one case who showed no enhancement.

Conclusion

MRI can be helpfull in the pretreatment assessment and int he follow-up of Peyronie’s disease.