1,083 research outputs found
Corticotropin-releasing factor receptors couple to multiple g-proteins to activate diverse intracellular signaling pathways in mouse hippocampus: role in neuronal excitability and associative learning
No full textCorticotropin-releasing factor (CRF) exerts a key neuroregulatory control on stress responses in various regions of the mammalian brain, including the hippocampus. Using hippocampal slices, extracts, and whole animals, we investigated the effects of human/rat CRF (h/rCRF) on hippocampal neuronal excitability and hippocampus-dependent learning in two mouse inbred strains, BALB/c and C57BL/6N. Intracellular recordings from slices revealed that application of h/rCRF increased the neuronal activity in both mouse inbred strains. Inhibition of protein kinase C (PKC) by bisindolylmaleimide I (BIS-I) prevented the h/rCRF effect only in hippocampal slices from BALB/c mice but not in slices from C57BL/6N mice. Inhibition of cAMP-dependent protein kinase (PKA) by H-89 abolished the h/rCRF effect in slices from C57BL/6N mice, with no effect in slices from BALB/c mice. Accordingly, h/rCRF elevated PKA activity in hippocampal slices from C57BL/6N mice but increased only PKC activity in the hippocampus of BALB/c mice. These differences in h/rCRF signal transduction were also observed in hippocampal membrane suspensions from both mouse strains. In BALB/c mice, hippocampal CRF receptors coupled to Gq/11 during stimulation by h/rCRF, whereas they coupled to Gs, Gq/11, and Gi in C57BL/6N mice. As expected on the basis of the slice experiments, h/rCRF improved context-dependent fear conditioning of BALB/c mice in behavioral experiments, and BIS-I prevented this effect. However, although h/rCRF increased neuronal spiking in slices from C57BL/6N mice, it did not enhance conditioned fear. These results indicate that the CRF system activates different intracellular signaling pathways in mouse hippocampus and may have distinct effects on associative learning depending on the mouse strain investigated
Solid state 2H NMR molecular spectra: separation of spectral components by guest alignment in an axially oriented polymeric crystalline host phase
No full textChlorinated guest orientation and mobility in the clathrate phase structure with syndiotactic polystyrene
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Geometry of Complex Molecular Motions of Guest Molecules in Polymers from Solid State H-2 NMR
No full textNanoporous systems provide interesting possibilities to confine molecules to be used for specific functions, e.g., as switches, in sensorics, or in separation. Such behavior partially mimics biological systems, where enzymes with specific cavities exhibit exquisite binding discrimination and reactivity.1d,1e Recent advances in solid-state inclusion compounds produced an extraordinary variety of cavities that encapsulate guests through noncovalent forces and can be customized through molecular design to control their solid-state properties and guest reactivity. Crystalline polymers offer the additional advantage of processability and alignment due tomechanical forces. In this context, the nanoporous δ and ε crystalline phases of syndiotactic polystyrene (s-PS), obtained by guest removal with supercritical carbon dioxide from cocrystalline phase, offer promising applications in chemical separation (mainly air/water purification), in sensorics, and optical applications
An epidemiological assessment of lens opacifications that impaired vision in patients injected with radium-224
No full textThe incidence of lens opacifications that impaired vision (cataract) was analyzed among 831 patients who were injected with known dosages of 224Ra in Germany shortly after World War II. The dependence of the incidence on dosage, i.e., injected activity per unit body weight, and on time after treatment was determined. The observations are equally consistent with proportionality of the incidence of cataract to the square of dosage or with a linear dependence beyond a threshold of 0.5 MBq/kg. The possibility of a linear dependence without threshold was strongly rejected (P less than 0.001). The analysis of temporal dependences yielded a component that was correlated with the injected amount of 224Ra and a component that was uncorrelated. The former was inferred by a maximum likelihood analysis to increase approximately as the square of the time after treatment. The component unrelated to the treatment was found to increase steeply with age and to become dominant within the collective of patients between age 50 and 60. The relative magnitudes of the two components were such that a fraction of 55 to 60% of the total of 58 cataracts had to be ascribed to the dose-related incidence. Impaired vision due to cataract was diagnosed before age 54 in 25 cases. In terms of injected activity per unit body weight no dependence of the sensitivity on age was found; specifically there was no indication of a faster occurrence of the treatment-related cataracts in patients treated at older ages
Characterization of granule-like structures in non-endocrine cells
No full textAll eukaryotic cells have transport pathways to constitutively secrete proteins. Endocrine, neuroendocrine, and exocrine cells in addition have a regulated secretory pathway that serves the controlled release of hormones, neuropeptides or digestive enzymes. In the transGolgi network (TGN) precursors of regulated secretory proteins are segregated and packaged in a concentrated form in secretory granules where they are processed and activated before release in response to an extracellular stimulus by fusion with the plasma membrane. Little is known about the machinery involved in the generation of secretory granules. The current models propose that luminal proteins interact with transmembrane receptors and/or that cargo proteins form insoluble aggregates due to milieu acidification resulting in membrane association and formation of a secretory granule. We discovered that even in non-endocrine cells the expression of regulated cargo proteins is sufficient to induce granule-like structures. We showed that cargo proteins accumulate in the TGN where they are sorted into membrane vesicles. These structures did not colocalize with organelle markers for the endoplasmic reticulum, the Golgi, the TGN, lysosomes, and endosomes. The helper cargo proteins secretogranin II and chromogranin B were stored intracellularly, and their secretion could be stimulated by addition of a calcium ionophore. Considerable differences were observed in efficiency of induction and in morphology of granule-like structures depending on the expressed cargo protein. Granins were more efficient, capable to sort other cargo proteins, and modulate the size of granule-like structures. Some accessory proteins such as the proprotein convertases PC3 and PC6A but also the IP3-R/Ca2+ channel sorted into granule-like structures when coexpressed with secretogranin II. The data suggest that secretory granule formation is a self-assembly process which is optimized by an endocrine-specific machinery. Carboxypeptidase E was proposed to function as a sorting receptor with an unconventional transmembrane anchor similar to PC2 and PC3. The topology of theses proteins is particularly important for granule sorting and association with putative interaction partners. A systematic analysis showed that PC3 is a luminal protein suggesting that granule targeting of PCs and CPE is not achieved by direct interaction with cytosolic proteins
Magnetic resonance imaging of H-1 long lived states derived from parahydrogen induced polarization in a clinical system
No full textHyperpolarization is a powerful tool to overcome the low sensitivity of nuclear magnetic resonance (NMR). However, applications are limited due to the short lifetime of this non equilibrium spin state caused by relaxation processes. This issue can be addressed by storing hyperpolarization in slowly decaying singlet spin states which was so far mostly demonstrated for non-proton spin pairs, e.g. 13C-13C. Protons hyperpolarized by parahydrogen induced polarization (PHIP) in symmetrical molecules, are very well suited for this strategy because they naturally exhibit a long-lived singlet state. The conversion of the NMR silent singlet spin state to observable magnetization can be achieved by making use of singlet-triplet level anticrossings. In this study, a low-power radiofrequency pulse sequence is used for this purpose, which allows multiple successive singlet-triplet conversions. The generated magnetization is used to record proton images in a clinical magnetic resonance imaging (MRI) system, after 3 min waiting time. Our results may open unprecedented opportunities to use the standard MRI nucleus 1H for e.g. metabolic imaging in the future.Fil: Graafen, Dirk. Max Planck Institute for Polymer Research; Alemania. Johannes Gutenberg University Medical Center; AlemaniaFil: Franzoni, Maria Belen. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Max Planck Institute for Polymer Research; AlemaniaFil: Schreiber, Laura M.. Johannes Gutenberg University Medical Center; AlemaniaFil: Spiess, Hans W.. Max Planck Institute for Polymer Research; AlemaniaFil: Münnemann, Kerstin. Max Planck Institute for Polymer Research; Alemani
Dynamic insertion of membrane proteins at the endoplasmic reticulum
No full textMost eukaryotic membrane proteins are cotranslationally integrated into the endoplasmic reticulum membrane by the Sec61 translocation complex. They are targeted to the translocon by hydrophobic signal sequences which induce the translocation of either their N- or C-terminal sequence. Signal sequence orientation is largely determined by charged residues flanking the apolar sequence (the positive-inside rule), folding properties of the N-terminal segment, and the hydrophobicity of the signal. Recent in vivo experiments suggest that N-terminal signals initially insert into the translocon head-on to yield a translocated Nterminus. Driven by a local electrical potential, the signal may invert its orientation and translocate the C-terminal sequence. Increased hydrophobicity slows down inversion by stabilizing the initial bound state. In vitro crosslinking studies indicate that signals rapidly contact lipids upon entering the translocon. Together with the recent crystal structure of the homologous SecYEβ translocation complex of Methanococcus jannaschii, which did not reveal an obvious hydrophobic binding site for signals within the pore, a model emerges in which the translocon allows the lateral partitioning of hydrophobic segments between the aqueous pore and the lipid membrane. Signals may return into the pore for reorientation until translation is terminated. Subsequent transmembrane segments in multispanning proteins behave similarly and contribute to the overall topology of the protein. This thesis was aimed at investigating the integration of single- and doublespanning membrane proteins in mammalian cells. The first part consisted of probing the environment of the signal while its orientation is determined by inserting different hydrophobic residues at various positions throughout a uniform oligo-leucine signal sequence. The resulting topologies revealed a strikingly symmetric position dependence specifically for bulky aromatic amino acids, reflecting the structure of a lipid bilayer. The results support the model that during topogenesis in vivo the signal sequence is exposed to the lipid membrane. The second part consisted of the determination of the kinetics of double-spanning protein topogenesis. The results confirmed that major reorientation of the polypeptide my occur when a second topogenic sequence, conflicting with a first one, enters the translocon. They also showed that the time window for protein reorientation differs for different types of substrate
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