Dielectric properties of hemoglobin and myoglobin. I. Influence of solvent and particle size on the dielectric dispersion

Dielectric dispersion measurements with aqueous solutions of hemoglobin and myoglobin have been performed in the frequency range from 100 kcps to 15 Mcps. The influence of preparation, particle size, and solvent conditions was studied. The results are analyzed in terms of an orientational polarization mechanism.     

Ion gradient and photoreceptor sensitivity

Summary In superposition eyes of moths (Deilephila elpenor, Manduca sexta) and a neuropteran (Ascalaphus macaronius) receptor excitation and adaptation depend on the limited store of available ion charges in the extra-cellular space.Na⁺ is the main charge carrier necessary for excitation. Receptor mass responses (measured by extracellular electrodes) can, however, be elicited also after complete removal of Na⁺ from the extra-ommatidial space. Responses are also obtained when Na⁺ is partially replaced by Ca⁺⁺ or Mg⁺⁺. These results suggest that the extra-ommatidial space is separated from the intra-ommatidial (rhabdomeric) extra-cellular space. Ion flow between these spaces is slow. The ion exchange during illumination probably takes place over the rhabdomeric part of the photoreceptor membrane.The Na⁺ concentration in the rhabdomeric extracellular space is about 150 mM, as shown by flame photometry. This result supports the assumption that this space is the common Na⁺ store for the three receptor types (UV, green, violet).Positive (optic lobe positive) DC polarization of the retina causes a reduction in the amplitude of the mass responses to light. After cessation of the polarization the amplitude increases with a time constant similar to that after strong illumination. Negative polarization accelerates the rate of increase in amplitude during dark adaptation, while positive polarization retards the increase. These results suggest that one important factor determining the time course of sensitivity increase during dark adaptation is the reestablishment of the Na⁺ gradient over the rhabdomeric membrane.There is a strong electric coupling between the three receptor types in the ommatidium, since all receptors share the same limited intra-ommatidial extra-cellular ion store. Strong illumination of one receptor reduces the ion gradient (extra- to intracellular) also for the other receptors (not absorbing the light). Thereby the sensitivity of the non-illuminated receptors is also reduced. The electric coupling probably improves the wavelength discrimination by the receptors, by keeping almost constant the relative sensitivity of all three receptor types during shortlasting strong selective adaptation of one or two receptor types.The time course of the resistance change over the receptor membrane (measured extra-cellularly) during and after illumination, suggests that during illumination the Na⁺ influx is reduced, and that the ion gradient over the receptor membrane is at least partially re-established already during the illumination.We are grateful to Dr. A.H. Baumhover (United States Department of Agriculture, Agricultural Research Service, Oxford, North Carolina 27565, USA) for supplying theManduca pupae. The work was supported by the Deutsche Forschungsgemeinschaft, SFB 114 and Rezeptorphysiologie; and by Karolinska Institutets Fonder.     

Pan-Mammalian Target of Rapamycin (mTOR) Inhibitor AZD8055 Primes Rhabdomyosarcoma Cells for ABT-737-induced Apoptosis by Down-regulating Mcl-1 Protein

The PI3K/mammalian Target of Rapamycin (mTOR) pathway is often aberrantly activated in rhabdomyosarcoma (RMS) and represents a promising therapeutic target. Recent evaluation of AZD8055, an ATP-competitive mTOR inhibitor, by the Preclinical Pediatric Testing Program showed in vivo antitumor activity against childhood solid tumors, including RMS. Therefore, in the present study, we searched for AZD8055-based combination therapies. Here, we identify a new synergistic lethality of AZD8055 together with ABT-737, a BH3 mimetic that antagonizes Bcl-2, Bcl-x_L, and Bcl-w but not Mcl-1. AZD8055 and ABT-737 cooperate to induce apoptosis in alveolar and embryonal RMS cells in a highly synergistic fashion (combination index < 0.2). Synergistic induction of apoptosis by AZD8055 and ABT-737 is confirmed on the molecular level, as AZD8055 and ABT-737 cooperate to trigger loss of mitochondrial membrane potential, activation of caspases, and caspase-dependent apoptosis that is blocked by the pan-caspase inhibitor Z-VAD-fmk. Similar to AZD8055, the PI3K/mTOR inhibitor NVP-BEZ235, the PI3K inhibitor NVP-BKM120 and Akt inhibitor synergize with ABT-737 to trigger apoptosis, whereas no cooperativity is found for the mTOR complex 1 inhibitor RAD001. Interestingly, molecular studies reveal a correlation between the ability of different PI3K/mTOR inhibitors to potentiate ABT-737-induced apoptosis and to suppress Mcl-1 protein levels. Importantly, knockdown of Mcl-1 increases ABT-737-induced apoptosis similar to AZD8055/ABT-737 cotreatment. This indicates that AZD8055-mediated suppression of Mcl-1 protein plays an important role in the synergistic drug interaction. By identifying a novel synergistic interaction of AZD8055 and ABT-737, our findings have important implications for the development of molecular targeted therapies for RMS.     

Wie sich Oasen‐Bananen gegen ihre Feinde wehren. Uralter Toleranzmechanismus im Oman entdeckt

Until recently little was known about the crop diversity in the Sultanate of Oman, situated at the NE tip of the Arabian Peninsula. Interdisciplinary research in the often millenia‐old oases provide evidence for their role as reservoirs for plant genetic resources of ancient varieties of wheat and banana. Two newly discovered banana clones show a highly efficient biochemical defense mechanisms against some of the most devastating pests and diseases of banana. If these mechanisms can be properly understood and exploited in breeding programs, may have major impact on the commercial production of edible banana.     

Resource use efficiency in urban and peri-urban sheep, goat and cattle enterprises

Urban livestock husbandry receives growing attention given the increasing urban demand for livestock products. At the same time, little is known about the resource use efficiency in urban livestock enterprises and eventual negative externalities. In livestock production, feeds are an important resource whose nutrients are transformed into products (meat and milk) to generate financial return to the producer. The lack of knowledge on nutrient supply through feed might lead to oversupply with severe environmental impacts. In Niamey, a typical West African city and capital of the Republic of Niger, urban livestock production is constrained by feed scarcity, especially during the dry season. Here, the issue of resource use efficiency was studied in 13 representative and differently managed sheep/goat and cattle enterprises characterized by high and low feed inputs, respectively, during a period of 28 months. Nitrogen (N), phosphorus (P) and potassium (K) inflows into each farm through livestock feeds and outflows through manure were determined using a semi-structured questionnaire; interviews were accompanied by regular weighing of feed supplied and dung produced. Live weight gain (LWG) and efficiency of conversion of total feed dry matter offered (kg TDMO/kg LWG) were computed along with nutrient balances (NBs) per metabolic body mass (kg0.75). NBs (per kg0.75/day) in the high-input (HI) sheep/goat enterprises were +1762.4 mg N, +127.2 mg P and +1363.5 mg K and were significantly greater (P < 0.05) than those in low-input (LI) units (+69.1 mg N, -98.3 mg P and +16.5 mg K). In HI cattle enterprises, daily balances averaged +454.1 mg N, +40.1 mg P and +341.8 mg K compared to +34.4 mg N, -9.0 mg P and +68.3 mg K (P > 0.05) in LI cattle systems. All systems were characterized by poor conversion efficiencies of offered feed, which ranged from 13.5 to 46.1 kg TDMO/kg LWG in cattle and from 15.7 to 43.4 kg TDMO/kg LWG in sheep/goats. LWG in HI sheep/goats was 53 g/day in the rainy season, 86 g/day in the hot dry season and 104 g/day in the cool dry season, while HI cattle lost 79 g/day in the hot dry season and gained 121 g/day and 92 g/day in the cool dry and rainy seasons, respectively. The data indicate that there is nutrient wasting and scope for improvement of feeding strategies in Niamey's livestock enterprises, which might also decrease nutrient losses to the urban environment.     

Similar hypotensive responses to resistance exercise with and without blood flow restriction

Low intensity resistance exercise (RE) with blood flow restriction (BFR) has gained attention in the literature due to the beneficial effects on functional and morphological variables, similar to those observed during traditional RE without BFR, while the effects of BFR on post-exercise hypotension remain unclear. The aim of the present study was to compare the blood pressure (BP) response of trained normotensive individuals to RE with and without BFR. In this cross-over randomized trial, eight male subjects (23.8 ± 4 years, 74 ± 3 kg, 174 ± 4 cm) completed two exercise protocols: traditional RE (3 x 10 repetitions at 70% one-repetition maximum [1-RM]) and low intensity RE (3 x 15 repetitions at 20% 1-RM) with BFR. Blood pressure measurements were performed after 15 min of seated rest (0), immediately after and 10 min, 20 min, 30 min, 40 min, 50 min and 60 min after the experimental sessions. Similar hypotensive effects for systolic BP (SBP) were observed for both protocols (P < 0.05) after exercise, with no differences between groups (P > 0.05) and no statistically significant difference for diastolic BP (P > 0.05). These results suggest that in normotensive trained individuals, both traditional RE and RE with BFR induce hypotension for SBP, which is important to prevent cardiovascular disturbances.     

Classification of DNA methylation patterns in tumor cell genomes using a CpG island microarray

Our group has initiated experiments to epigenetically profile CpG island hypermethylation in genomic DNA from tissue specimens of head and neck squamous cell carcinoma (HNSCC) using a microarray of 12,288 CpG island clones. Our technique, known as a methylation-specific restriction enzyme (MSRE) analysis, is a variation of the differential methylation hybridization (DMH) technique, in that it is not an array comparison of two DNA samples using methylation-specific restriction enzymes. Instead, it is a comparison of a single DNA sample's response to a methylation-sensitive restriction enzyme (HpaII) and its corresponding methylation-insensitive isoschizomer (MspI). Estimation of the reproducibility of this microarray assay by intraclass correlation (ICC) demonstrated that in four replicate experiments for three tumor specimens, the ICC observed for a given tumor specimen ranged from 0.68 to 0.85 without filtering of data. Repeated assays achieved 87% concordance or greater for all tumors after filtering of array data by fluorescence intensity. We utilized hierarchical clustering on a population of 37 HNSCC samples to cluster tumor samples with similar DNA methylation profiles. Supervised learning techniques are now being utilized to allow us to identify associations between specific epigenetic signatures and clinical parameters. Such techniques will allow us to identify select groups of CpG island loci that could be used as epigenetic markers for both diagnosis and prognosis in HNSCC.     

The Distribution of Grazing Pressure in Relation to Vegetation Resources in Semi-arid West Africa: The Role of Herding

In semi-arid West Africa, livestock are increasingly managed by sedentary producers in close proximity to expanding cropped lands. To evaluate the agricultural and environmental implications of this trend, a study was conducted to investigate the effect of grazing management on the spatial distribution of grazing pressure, the forage provided animals during the grazing period, and local herd-forage ratios across three agropastoral landscapes characterized by varying cultivation pressure. During the 19-month study period, data on herbaceous vegetation, livestock populations, and grazing itineraries were collected. These data were referenced to land units averaging 70 ha in area. Using this approach, each of 3,819 grazing itineraries was characterized as to: 1. the sum of the products of the palatable forage mass of a particular land unit and the time spent grazing by the herd within that unit (FAT, expressed in kg-hours ha⁻¹); and 2. the average palatable herbaceous forage mass encountered by livestock across the itinerary weighted by the time spent in the land units crossed (FA, expressed in kg ha⁻¹). The spatial dispersion of livestock grazing around human settlements was found to decline with a reduction in herding labor investment (herded>herd-release>free pasture). Multiple regression analyses of itinerary data demonstrate that both FAT and FA also decline with a reduction in herding labor investment. Herded and herd-release managed livestock were offered more palatable forage and grazed areas of higher forage availability than free-pastured animals. This supports arguments that as the investment of time and effort into herding declines, feed supply to livestock will decline and the potential for grazing-induced environmental change will increase.