Cholinergic Stimulation of Inositol Phosphate Formation in Bovine Adrenal Chromaffin Cells: Distinct Nicotinic and Muscarinic Mechanisms

The ability of cholinergic agonists to activate phospholipase C in bovine adrenal chromaffin cells was examined by assaying the production of inositol phosphates in cells prelabeled with [ 3 H]inositol. We found that both nicotinic and muscarinic agonists increased the accumulation of [ 3 H]inositol phosphates (mainly inositol monophos-phate) and that the effects mediated by the two types of receptors were independent of each other. The production of inositol phosphates by nicotinic stimulation required extracellular Ca 2+ and was maximal at 0.2 m M Ca 2+ . Increasing extracellular Ca 2+ from 0.22 to 2.2 m M increased the sensitivity of inositol phosphates formation to stimulation by submaximal concentrations of 1,1-dimethyl-4-phenyl-piperazinium iodide (DMPP) but did not enhance the response to muscarine. Elevated K + also stimulated Ca 2+ -dependent [ 3 H]inositol phosphate production, presumably by a non-receptor-mediated mechanism. The Ca 2+ channel antagonists D600 and nifedipine inhibited the effects of DMPP and elevated K + to a greater extent than that of muscarine. Ca 2+ (0.3–10 Μ M ) directly stimulated the release of inositol phosphates from digitonin-permeabilized cells that had been prelabeled with [ 3 H]inositol. Thus, cholinergic stimulation of bovine adrenal chromaffin cells results in the activation of phospholipase C by distinct muscarinic and nicotinic mechanisms. Nicotinic receptor stimulation and elevated K + probably increased the accumulation of inositol phosphates through Ca 2+ influx and a rise in cytosolic Ca 2+ . Because Ba 2+ caused catechol-amine secretion but did not enhance the formation of inositol phosphates, phospholipase C activation is not required for exocytosis. However, diglyceride and wyo -inositol 1,4,5-trisphosphate produced during cholinergic stimulation of chromaffin cells may modulate secretion and other cellular processes by activating protein kinase C and/or releasing Ca 2+ from intracellular stores.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/65738/1/j.1471-4159.1987.tb01037.x.pd

A prospective earthquake forecast experiment in the western Pacific

Since the beginning of 2009, the Collaboratory for the Study of Earthquake Predictability (CSEP) has been conducting an earthquake forecast experiment in the western Pacific. This experiment is an extension of the Kagan—Jackson experiments begun 15 years earlier and is a prototype for future global earthquake predictability experiments. At the beginning of each year, seismicity models make a spatially gridded forecast of the number of Mw≥ 5.8 earthquakes expected in the next year. For the three participating statistical models, we analyse the first two years of this experiment. We use likelihood-based metrics to evaluate the consistency of the forecasts with the observed target earthquakes and we apply measures based on Student's t-test and the Wilcoxon signed-rank test to compare the forecasts. Overall, a simple smoothed seismicity model (TripleS) performs the best, but there are some exceptions that indicate continued experiments are vital to fully understand the stability of these models, the robustness of model selection and, more generally, earthquake predictability in this region. We also estimate uncertainties in our results that are caused by uncertainties in earthquake location and seismic moment. Our uncertainty estimates are relatively small and suggest that the evaluation metrics are relatively robust. Finally, we consider the implications of our results for a global earthquake forecast experimen

Interstellar neutral helium in the heliosphere from IBEX observations. V. Observations in IBEX-Lo ESA steps 1, 2, & 3

Direct-sampling observations of interstellar neutral (ISN) He by Interstellar Boundary Explorer (IBEX) provide valuable insight into the physical state of and processes operating in the interstellar medium ahead of the heliosphere. The ISN He atom signals are observed at the four lowest ESA steps of the IBEX-Lo sensor. The observed signal is a mixture of the primary and secondary components of ISN He and H. Previously, only data from one of the ESA steps have been used. Here, we extended the analysis to data collected in the three lowest ESA steps with the strongest ISN He signal, for the observation seasons 2009-2015. The instrument sensitivity is modeled as a linear function of the atom impact speed onto the sensor's conversion surface separately for each ESA step of the instrument. We found that the sensitivity increases from lower to higher ESA steps, but within each of the ESA steps it is a decreasing function of the atom impact speed. This result may be influenced by the hydrogen contribution, which was not included in the adopted model, but seems to exist in the signal. We conclude that the currently accepted temperature of ISN He and velocity of the Sun through the interstellar medium do not need a revision, and we sketch a plan of further data analysis aiming at investigating ISN H and a better understanding of the population of ISN He originating in the outer heliosheath.Comment: 20 pages, 5 figures, 5 tables, accepted for publication in the The Astrophysical Journa

Development of Onchocerca volvulus in humanized NSG mice and detection of parasite biomarkers in urine and serum.

BACKGROUND: The study of Onchocerca volvulus has been limited by its host range, with only humans and non-human primates shown to be susceptible to the full life cycle infection. Small animal models that support the development of adult parasites have not been identified. METHODOLOGY/PRINCIPAL FINDINGS: We hypothesized that highly immunodeficient NSG mice would support the survival and maturation of O. volvulus and alteration of the host microenvironment through the addition of various human cells and tissues would further enhance the level of parasite maturation. NSG mice were humanized with: (1) umbilical cord derived CD34+ stem cells, (2) fetal derived liver, thymus and CD34+ stem cells or (3) primary human skeletal muscle cells. NSG and humanized NSG mice were infected with 100 O. volvulus infective larvae (L3) for 4 to 12 weeks. When necropsies of infected animals were performed, it was observed that parasites survived and developed throughout the infection time course. In each of the different humanized mouse models, worms matured from L3 to advanced fourth stage larvae, with both male and female organ development. In addition, worms increased in length by up to 4-fold. Serum and urine, collected from humanized mice for identification of potential biomarkers of infection, allowed for the identification of 10 O. volvulus-derived proteins found specifically in either the urine or the serum of the humanized O. volvulus-infected NSG mice. CONCLUSIONS/SIGNIFICANCE: The newly identified mouse models for onchocerciasis will enable the development of O. volvulus specific biomarkers, screening for new therapeutic approaches and potentially studying the human immune response to infection with O. volvulus

Intracellular Ca2+ activates phospholipase C

It is well established that a receptor-mediated mechanism, perhaps involving a guanine nucleotide binding protein, directly activates polyphosphoinositide-specific phospholipase C. Recent evidence indicates that in excitable tissues a rise in cytosolic Ca2+ can also activate the phospholipase C. The activation of phospholipase C by Ca2+ can be a direct effect rather than a result of the Ca2+-dependent release of neurotransmitters which activate phospholipase C through a receptor-mediated mechanism. Ca2+-activated phospholipase C may represent a positive feedback system for Ca2+: small increases in cytosolic Ca2+ induced by Ca2+ influx across the plasma membrane may result in higher cytosolic Ca2+ concentrations due to IP3-induced release of Ca2+ from intracellular stores. The activation of phospholipase C by Ca2+ may also provide a mechanism for diacylglycerol generation and protein kinase C activation following Ca2+ influx. Thus, the regulation of phospholipase C activity by Ca2+ may be physiologically important in regulating cytosolic Ca2+ and protein kinase C in excitable tissues.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/27573/1/0000617.pd

TRIANGULATION OF THE INTERSTELLAR MAGNETIC FIELD

Determining the direction of the local interstellar magnetic field (LISMF) is important for understanding the heliosphere's global structure, the properties of the interstellar medium, and the propagation of cosmic rays in the local galactic medium. Measurements of interstellar neutral atoms by Ulysses for He and by SOHO/SWAN for H provided some of the first observational insights into the LISMF direction. Because secondary neutral H is partially deflected by the interstellar flow in the outer heliosheath and this deflection is influenced by the LISMF, the relative deflection of H versus He provides a plane—the so-called B–V plane in which the LISMF direction should lie. Interstellar Boundary Explorer (IBEX) subsequently discovered a ribbon, the center of which is conjectured to be the LISMF direction. The most recent He velocity measurements from IBEX and those from Ulysses yield a B–V plane with uncertainty limits that contain the centers of the IBEX ribbon at 0.7–2.7 keV. The possibility that Voyager 1 has moved into the outer heliosheath now suggests that Voyager 1's direct observations provide another independent determination of the LISMF. We show that LISMF direction measured by Voyager 1 is >40° off from the IBEX ribbon center and the B–V plane. Taking into account the temporal gradient of the field direction measured by Voyager 1, we extrapolate to a field direction that passes directly through the IBEX ribbon center (0.7–2.7 keV) and the B–V plane, allowing us to triangulate the LISMF direction and estimate the gradient scale size of the magnetic field