Conductance Ratios and Cellular Identity

Recent experimental evidence suggests that coordinated expression of ion channels plays a role in constraining neuronal electrical activity. In particular, each neuronal cell type of the crustacean stomatogastric ganglion exhibits a unique set of positive linear correlations between ionic membrane conductances. These data suggest a causal relationship between expressed conductance correlations and features of cellular identity, namely electrical activity type. To test this idea, we used an existing database of conductance-based model neurons. We partitioned this database based on various measures of intrinsic activity, to approximate distinctions between biological cell types. We then tested individual conductance pairs for linear dependence to identify correlations. Contrary to experimental evidence, in which all conductance correlations are positive, 32% of correlations seen in this database were negative relationships. In addition, 80% of correlations seen here involved at least one calcium conductance, which have been difficult to measure experimentally. Similar to experimental results, each activity type investigated had a unique combination of correlated conductances. Finally, we found that populations of models that conform to a specific conductance correlation have a higher likelihood of exhibiting a particular feature of electrical activity. We conclude that regulating conductance ratios can support proper electrical activity of a wide range of cell types, particularly when the identity of the cell is well-defined by one or two features of its activity. Furthermore, we predict that previously unseen negative correlations and correlations involving calcium conductances are biologically plausible.     

Change in climatically suitable breeding distributions reduces hybridization potential between Vermivora warblers

Aim

Climate change is affecting the distribution of species and subsequent biotic interactions, including hybridization potential. The imperiled Golden-winged Warbler (GWWA) competes and hybridizes with the Blue-winged Warbler (BWWA), which may threaten the persistence of GWWA due to introgression. We examined how climate change is likely to alter the breeding distributions and potential for hybridization between GWWA and BWWA.

Location

North America.

Methods

We used GWWA and BWWA occurrence data to model climatically suitable conditions under historical and future climate scenarios. Models were parameterized with 13 bioclimatic variables and 3 topographic variables. Using ensemble modeling, we estimated historical and modern distributions, as well as a projected distribution under six future climate scenarios. We quantified breeding distribution area, the position of and amount of overlap between GWWA and BWWA distributions under each climate scenario. We summarized the top explanatory variables in our model to predict environmental parameters of the distributions under future climate scenarios relative to historical climate.

Results

GWWA and BWWA distributions are projected to substantially change under future climate scenarios. GWWA are projected to undergo the greatest change; the area of climatically suitable breeding season conditions is expected to shift north to northwest; and range contraction is predicted in five out of six future climate scenarios. Climatically suitable conditions for BWWA decreased in four of the six future climate scenarios, while the distribution is projected to shift east. A reduction in overlapping distributions for GWWA and BWWA is projected under all six future climate scenarios.

Main Conclusions

Climate change is expected to substantially alter the area of climatically suitable conditions for GWWA and BWWA, with the southern portion of the current breeding ranges likely to become climatically unsuitable. However, interactions between BWWA and GWWA are expected to decline with the decrease in overlapping habitat, which may reduce the risk of genetic introgression.     

Enrichment of adeno-associated virus serotype 5 full capsids by anion exchange chromatography with dual salt elution gradients

Adeno-associated virus-based gene therapies have demonstrated substantial therapeutic benefit for the treatment of genetic disorders. In manufacturing processes, viral capsids are produced with and without the encapsidated gene of interest. Capsids devoid of the gene of interest, or “empty” capsids, represent a product-related impurity. As a result, a robust and scalable method to enrich full capsids is crucial to provide patients with as much potentially active product as possible. Anion exchange chromatography has emerged as a highly utilized method for full capsid enrichment across many serotypes due to its ease of use, robustness, and scalability. However, achieving sufficient resolution between the full and empty capsids is not trivial. In this work, anion exchange chromatography was used to achieve empty and full capsid resolution for adeno-associated virus serotype 5. A salt gradient screen of multiple salts with varied valency and Hofmeister series properties was performed to determine optimal peak resolution and aggregate reduction. Dual salt effects were evaluated on the same product and process attributes to identify any synergies with the use of mixed ion gradients. The modified process provided as high as ≥75% AAV5 full capsids (≥3-fold enrichment based on the percent full in the feed stream) with near baseline separation of empty capsids and achieved an overall vector genome step yield of >65%.     

A Ca2+-stimulated adenosine triphosphatase in Golgi-enriched membranes of lactating murine mammary tissue.

A membrane fraction isolated from lactating murine mammary tissue and enriched for the Golgi membrane marker enzyme galactosyltransferase exhibited Ca2+-stimulated ATPase activity (Ca-ATPase) in 20 microM-free Mg2+ and 10 microM-MgATP, with an apparent Km for Ca2+ of 0.8 microM. Exogenous calmodulin did not enhance Ca2+ stimulation, nor could Ca-ATPase activities be detected in millimolar total Mg2+ and ATP. When assayed with micromolar Mg2+ and MgATP the Ca-ATPases of skeletal-muscle sarcoplasmic reticulum and of calmodulin-enriched red blood cell plasma membranes were half-maximally activated by 0.1 microM- and 0.6 microM-Ca2+ respectively. All three Ca-ATPases were inhibited by similar micromolar concentrations of trifluoperazine, but the Golgi activity was unaffected by quercetin in concentrations which completely inhibited both the sarcoplasmic-reticulum and red-blood-cell enzymes. The results are consistent with the hypothesis that the high-affinity Ca-ATPase is responsible for the ATP-dependent Ca2+ transport exhibited by Golgi-enriched vesicles derived from lactating mammary gland [Neville, Selker, Semple & Watters (1981) J. Membr. Biol. 61, 97-105; West (1981) Biochim. Biophys. Acta 673, 374-386].     

Manipulation of platelet aggregation by prostaglandins and their fatty acid precursors: pharmacological basis for a therapeutic approach

Addition of the one-, two- or three- series endoperoxide to human platelet-rich plasma tend to suppress aggregation, through the action of their respective non-enzymatic breakdown products PGE1, PGD2, or PGD3 all of which elevate cyclic AMP levels. On the other hand, these stable primary products do not arise in appreciable amounts from intrinsic endoperoxides generated from either endogenous or exogenous free fatty acids. 5,8,11,14,17-Eicosapentaenoic acid (EPA) suppresses arachidonic acid (5,8,11,14-eicosatetraenoic acid) conversion by cyclooxygenase (as well as lipoxygenase) to aggregatory metabolites in platelets. Exogenously added EPA was capable of inhibiting PRP aggregation induced either by exogenous or endogenous (released by ADP or collagen) arachidonate. The hypothetical combination of an EPA-rich diet and a thromboxane synthetase inhibitor might abolish production of the pro-aggregatory species, thromboxane A2, and enhance formation of the anti-aggregatory metabolite, prostacyclin. Whereas EPA is not detectably metabolized by platelets, dihomo-gamma-linolenic acid (8,11,14-eicosatrienoic acid) is primarily converted by cyclooxygenase and thromboxane synthetase into the inactive metabolite, 12-hydroxyheptadecadienoic (HHD) acid. Pretreatment of human platelet suspensions with the thromboxane synthetase inhibitor imidazole unmasks the aggregatory property of PGH1 and DLL which was partially compromised by the PGE1 formed. The combination of the thromboxane synthetase inhibitor and an adenylate cyclase inhibitor unmasks a complete irreversible aggregation by DLL or PGH1. The basis of a dietary strategy that replaces AA with DLL must rely on the production by the platelet of an inactive metabolite (HHD) rather than thromboxane A2.     

Choice of hydrogen uptake (Hup) status in legume‐rhizobia symbioses

The H₂ is an obligate by-product of N-fixation. Recycling of H₂ through uptake hydrogenase (Hup) inside the root nodules of leguminous plants is often considered an advantage for plants. However, many of the rhizobium-legume symbioses found in nature, especially those used in agriculture are shown to be Hup⁻, with the plants releasing H₂ produced by nitrogenase activity from root nodules into the surrounding rhizosphere. Recent studies have suggested that, H₂ induces plant-growth-promoting rhizobacteria, which may explain the widespread of Hup⁻ symbioses in spite of the low energy efficiency of such associations. Wild legumes grown in Nova Scotia, Canada, were surveyed to determine if any plant-growth characteristics could give an indication of Hup choice in leguminous plants. Out of the plants sampled, two legumes, Securigera varia and Vicia cracca, showed Hup⁺ associations. Securigera varia exhibited robust root structure as compared with the other plants surveyed. Data from the literature and the results from this study suggested that plants with established root systems are more likely to form the energy-efficient Hup⁺ symbiotic relationships with rhizobia. Conversely, Hup⁻ associations could be beneficial to leguminous plants due to H₂-oxidizing plant-growth-promoting rhizobacteria that allow plants to compete successfully, early in the growing season. However, some nodules from V. cracca tested Hup⁺, while others were Hup⁻. This was similar to that observed in Glycine max and Pisum sativum, giving reason to believe that Hup choice might be affected by various internal and environmental factors.     

Synergistic Interactions of Eugenol-tosylate and Its Congeners with Fluconazole against Candida albicans

We previously reported the antifungal properties of a monoterpene phenol “Eugenol” against different Candida strains and have observed that the addition of methyl group to eugenol drastically increased its antimicrobial potency. Based on the results and the importance of medicinal synthetic chemistry, we synthesized eugenol-tosylate and its congeners (E1-E6) and tested their antifungal activity against different clinical fluconazole (FLC)- susceptible and FLC- resistant C. albicans isolates alone and in combination with FLC by determining fractional inhibitory concentration indices (FICIs) and isobolograms calculated from microdilution assays. Minimum inhibitory concentration (MIC) results confirmed that all the tested C. albicans strains were variably susceptible to the semi-synthetic derivatives E1-E6, with MIC values ranging from 1–62 μg/ml. The test compounds in combination with FLC exhibited either synergy (36%), additive (41%) or indifferent (23%) interactions, however, no antagonistic interactions were observed. The MICs of FLC decreased 2–9 fold when used in combination with the test compounds. Like their precursor eugenol, all the derivatives showed significant impairment of ergosterol biosynthesis in all C. albicans strains coupled with down regulation of the important ergosterol biosynthesis pathway gene-ERG11. The results were further validated by docking studies, which revealed that the inhibitors snugly fitting the active site of the target enzyme, mimicking fluconazole, may well explain their excellent inhibitory activity. Our results suggest that these compounds have a great potential as antifungals, which can be used as chemosensitizing agents with the known antifungal drugs.