1. Using Fura-2, we measured cytosolic free calcium concentrations in rod outer segments of the bullfrog (Rana catesbeiana) under a wide range of steady-state, adapting light intensities. We also ...measured rod circulating currents under the same adapting conditions. 2. Both the steady-state cytosolic free calcium concentration and the steady-state circulating current were halved by background lights that isomerized approximately 100 rhodopsin molecules per rod per second. A just-measurable reduction in calcium was evoked by a background 1/10 as bright. The steady-state calcium concentration and the steady-state circulating current were proportional to each other over the full range of intensities tested, the brightest of which suppresses the circulating current by 75% and reduces flash sensitivity by about two orders of magnitude relative to the rods' sensitivity in darkness. 3. Additional experiments, in which the Na+:Ca2+,K+ exchanger in the rod outer segment was inactivated while maintaining intracellular calcium at physiological levels, demonstrated that steady-state calcium concentrations in the outer segment are set only by the influx of calcium through the light-sensitive channels and its efflux via the Na+:Ca2+,K+ exchanger. We found no measurable light-induced release of calcium from internal stores and no evidence of any other calcium flux between the cytosol and intracellular compartments. 4. Taken together, these findings lead us to conclude that over the normal operating range of the rod, the selectivity of the cGMP-gated channels for calcium does not change as a result of background illumination. 5. Our data also suggest that a major role of calcium-dependent cGMP synthesis by guanylyl cyclase is to stabilize both the circulating current and the cytosolic free calcium concentration in darkness. This would minimize the dark noise of the rod and thereby increase the reliability with which dim stimuli can be detected in the dark-adapted state.
To evaluate the concept of a predetermined "setpoint" for iron stores, 20 healthy elderly individuals (12 blood donors and 8 nondonors) were studied to examine the effects of changes in iron stores ...on iron absorption. Oral iron-absorption tests revealed a statistically significant increase (P < 0.001) in iron absorption in donors, 7.4 +/- 3.6% (mean +/- SD) compared with 2.5 +/- 1.4% in nondonors. In a comparison of percent iron absorption with changes in baseline iron stores, a statistically significant correlation was noted (r2 = 0.702, P < 0.001). Thus, reductions in iron stores were correlated with increases in iron absorption. Basal gastric acid output was found to be within normal limits (1.62-10.20 mmol/h) in all elderly subjects and unrelated to iron stores. These findings are consistent with iron absorption being regulated according to the degree of depletion of iron stores from predonation values and is consistent with a proposed setpoint theory of iron stores.
The use of Ag
II as a removable template in synthetic porphyrin chemistry is described. Mild procedures for the insertion of Ag
II into chlorins and the demetallation of the chlorinatoAg
II complexes ...are delineated. The UV–vis spectra of the novel chlorinatoAg
II complexes are discussed. The diol cleavage products of
meso-tetraphenyl-2,3-diolchlorinatosilver(II) under a number of conditions are characterized and compared to those resulting from the cleavage of the corresponding free base diol chlorin or its Ni
II complex, highlighting the unique templating effect of Ag
II. The scopes and limits of electrospray ionization mass spectrometry (ESI-MS) for the analysis of Ag
II chlorins is described. The use of Ag
II as a templating metal is superior over Ni
II or Zn
II for the preparation of free base pyrrole-modified porphyrins along metal templated pathways.
Graphic
During February 2001 the CLUSTER satellites recorded a number of perigee passes through the midnight auroral zone. We concentrate on one pass, on 23 February 2001, when structured outflow was ...observed. Simultaneous observations of the aurora were available from the FUV instrument on IMAGE. The features in the ion outflow observed by the Cluster Ion Spectrometry (CIS) experiment are compared with the auroral activity. Observations from the multiple CLUSTER spacecraft are used to determine the velocity of the outflow structures. We find a good correspondence between the observed ion outflow and the auroral arcs, with the highest energy outflow corresponding to the brightest arcs. The features at the equatorward edge, which are trapped precipitating ions, are stationary. In addition, the increased velocity structure at the poleward edge is also stationary. However, the bulk of the ion outflow structures, which are observed between these boundaries, are moving equatorward with a velocity of roughly 7 km/s, which corresponds to a velocity of 0.7 km/s at 100 km. One feature is observed moving poleward, at the same time that the auroral arc is expanding poleward. Comparisons with the motion of the auroral arcs and with the convection velocity measured by the EDI instrument on CLUSTER show that the motion of the structures in general agrees with the convective motion of the field lines.
The Tat system transports folded proteins across bacterial and thylakoid membranes. In Gram-negative organisms, it is encoded by
tatABC genes and the system recognizes substrates bearing signal ...peptides with a conserved twin-arginine motif. Most Gram-positive organisms lack a
tatB gene, indicating major differences in organisation and/or mechanism. Here, we have characterized the essential targeting determinants that are recognized by a
Bacillus subtilis TatAC-type system, TatAdCd. Substitution by lysine of either of the twin-arginine residues in the TorA signal peptide can be tolerated, but the presence of twin-lysine residues blocks export completely. We show that additional determinants can be as important as the twin-arginine motif. Replacement of the −1 serine by alanine, in either the TorA or DmsA signal peptide, almost blocks export by either the
B. subtilis TatAdCd or
Escherichia coli TatABC systems, firmly establishing the importance of this −1 residue in these signal peptides. Surprisingly, the +2 leucine in the DmsA signal peptide (sequence SRRG
LV) appears to play an equally important role and substitution by alanine or phenylalanine blocks export by both the
B. subtilis and
E. coli systems. These data identify three distinct determinants, whose importance varies depending on the signal peptide in question. The data also show that the
B. subtilis TatAdCd and
E. coli TatABC systems recognize very similar determinants within their target peptides, and exhibit surprisingly similar responses to mutations within these determinants.
Antagonists of the corticotropin-releasing factor (CRF) neuropeptide should prove to be effective in treating stress and anxiety-related disorders. In an effort to identify antagonists with improved ...physicochemical properties, new tricyclic CRF(1) antagonists were designed, synthesized, and tested for biological activity. As a result of studies aimed at establishing a relationship between structure and CRF(1) binding affinity, NBI 35965 (12a) was identified as a high-affinity antagonist with a pK(i) value of 8.5. Compound 12a proved to be a functional CRF(1) antagonist with pIC(50) values of 7.1 and 6.9 in the in vitro CRF-stimulated cAMP accumulation and ACTH production assays, respectively, and 12a also reduced CRF or stress induced ACTH production in vivo.
On Jan 17, 2009, the legislative assembly for the Province of British Columbia met in an emergency session in the Provincial capital of Victoria. There was only one item on the agenda to be debated ...and voted upon. The City of Vancouver, set to host the 2010 Winter Olympics in less than thirteen months, had petitioned the Province for the authority to amend the city's Charter. This unprecedented request and its urgency was to permit the city to temporarily have authority to use its financial reserves and borrowing authority to bail out a private developer and its failing condominium development that was set to serve as the Athletes' Village for a two-week period in 2010. Without these special powers, the only lender the developer had been able to secure, a struggling New York hedge fund, would force the one-billion-dollar-plus project into default.
Pedogenic and diagenetic influences on void coating formation were studied in two paleosols from the Lower Cretaceous (Albian) Mill Creek Formation in southwestern Alberta, Canada, using detailed ...micromorphological, mineralogical and geochemical methods. The paleosols consist of alternating decimetre-scale beds of red, grey-green and variegated mudstone. Intermediate horizons (red and grey-green variegated mudstones) contain associations of pale yellow clay coatings, dark red clay coatings, Fe-depletion hypo-coatings and Fe-oxide quasi-coatings. SEM–EDX-ray analyses indicate that the dark reddish coatings are dominated by Si, Al and Fe, with subordinate amounts of K, Na, Ca, Mg and Ti. Pale yellow clay coatings have a higher Si content, and lower Al, K, Na, Ca and Fe contents relative to reddish coatings. Within the paleosol profiles, the distribution of clay minerals indicates: (1) an increase in discrete clay minerals downward, (2) a decrease in mixed layer illite-smectite downward and (3) an increase in chlorite upward. X-ray diffraction indicates that the pale yellow and dark red clay void coatings are polymineralic. Pale yellow clay coatings have a higher proportion of mixed layer illite–smectite and kaolinite, less chlorite and are less crystalline than dark reddish coatings. Despite a diagenetic overprint, including development of diffusion gleyans, degradation of organic matter, burial reddening, and probably some smectite illitization, both compositional and morphological gradients exist in the paleosol profiles and void coatings. These gradients are most likely related to depositional variations and to pedogenic development in the original soils under variable Eh–pH conditions in the presence of organic matter. Therefore, although the void coatings are altered (diagenetic features) their morphology, mineralogy and perhaps even some of their microchemistry is attributable to the presence of pedogenic precursors initially formed in soils similar to modern, temperate Alfisols and glossic soils.
Although selective transsphenoidal surgery is an effective treatment for pituitary-dependent Cushing's syndrome the definition of cure as distinct from improvement is unclear. Complete tumor removal ...should be associated with very low serum cortisol levels because of long-term suppression of normal corticotrophs but the optimum timing of this investigation after surgery has not been established. Eleven consecutive patients with surgical and histological confirmation of a corticotroph adenoma removed at transsphenoidal surgery for proven Cushing's disease were studied with 0900 h serum cortisol levels at 5-14 days and 6-12 weeks postoperatively. Patients were maintained on hydrocortisone 10 mg three times daily (final dose at 1800 h) pending recovery of the hypothalamic-pituitary axis which was assessed by periodic short tetracosactrin tests and continued remission of the condition was confirmed by low dose dexamethasone suppression testing. All patients achieved clinical resolution of their disease but four subsequently developed biochemical evidence of recurrence with incomplete suppression on low dose dexamethasone testing at 2-48 months after surgery. These patients had 0900 h serum cortisol levels of 124, 95, 186, and 265 nmol/L at 5-14 days and 334, 52, 130, and 240 nmol/L at 6-12 weeks postoperatively. The remaining seven patients, who are in remission after 8-83 (median 24) months of follow-up, demonstrated 0900 h serum cortisol levels of 30-75 (median 31) nmol/L at 5-14 days but lower levels at 6-12 weeks (< 20 nmol/L in three patients and 22, 30, 30, and 33 nmol/L in the remainder). In this series, serum cortisol measurements at 6-12 weeks after transsphenoidal surgery for Cushing's disease are lower than levels obtained within 2 weeks of surgery and appear to give better discrimination of continuing remission; levels less than 35 nmol/L suggest a favorable long-term outcome.
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