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  • 1
    ISSN: 1432-2013
    Keywords: Salivary gland ; Non-electrolyte permeability ; Reflection coefficient ; Acetylcholine ; Forskolin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Previous studies have suggested that the permeability of exocrine glands to non-electrolytes may change according to the nature and intensity of the stimuli evoking secretion. The purpose of this study was to define the nature of these permeability changes using a method that distinguishes diffusion from solvent drag. Isolated rabbit mandibular salivary glands were perfused with solutions containing14C-labelled non-electrolytes and stimulated with acetylcholine. Diffusive permeability coefficients (P) and solvent-drag filtration coefficients (1-σ) were estimated from the relationship between salivary non-electrolyte concentration and salivary flow rate. Filtration coefficients for urea, ethanediol, glycerol, erythritol and sucrose increased with acetylcholine concentration while, with the exception of urea, the diffusive permeabilities remained virtually unchanged. The effect of increasing acetylcholine concentration can best be explained by postulating an increase in the effective channel radius of the water secretion pathway from 0.40 nm to 0.45 nm together with a small increase in the fraction of the total water flow passing through larger non-selective pores. Forskolin had little effect on either of the permeability parameters except for a small increase in the diffusive permeability to ethanediol.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-2013
    Keywords: Salivary gland ; Intracellular pH ; 31P NMR spectroscopy ; Acetylcholine ; Amiloride ; DIDS ; Na+−H+ exchange
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Intracellular pH (pHi) was measured in the isolated, perfused rabbit mandibular salivary gland by31P NMR spectroscopy. In the unstimulated gland perfused with HCO 3 − /CO2-buffered Ringer's solution, pHi was 7.27±0.01. Continuous stimulation with acetylcholine elicited dose- and time-dependent changes in pHi. 10−6 mol/l acetylcholine caused a brief intracellular acidosis (−0.19±0.06 pH units) followed by an increase in pHi to a more alkaline steady-state value (7.33±0.02). In the absence of perfusate HCO 3 − or in the presence of 10−4 mol/l DIDS (4,4′-diisothiocyanatostilbene-2,2′-disulphonic acid), the transient acidosis was abolished and pHi increased rapidly to give a sustained alkalosis (7.49±0.03 and 7.44±0.03 respectively). In the presence of 10−3 mol/l amiloride, the response to acetylcholine was a rapid decrease in pHi to 7.02±0.02. The data suggest that, during perfusion with HCO 3 − /CO2-buffered solutions, stimulation with acetylcholine results in a transient loss of HCO 3 − from the acinar cells (causing a transient acidosis), and, independently, the activation of Na+−H+ exchange (causing a sustained alkalosis). In the unstimulated gland, DIDS and the HCO 3 − -free perfusate caused decreases in pHi to 7.12±0.02 and 7.04±0.01 respectively. In contrast, amiloride had little effect. The relatively high value of pHi maintained by the unstimulated gland is therefore probably not due to Na+−H+ exchange.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1432-1009
    Keywords: Acid precipitation ; Biomass nutrients ; Calcium ; Clearcutting ; Magnesium ; Nitrogen ; Phosphorus ; Potassium ; Soil leaching ; Soil nutrients ; Timber harvest ; Weathering ; Whole-tree harvest
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract Both harvest removal and leaching losses can deplete nutrient capital in forests, but their combined long-term effects have not been assessed previously. We estimated changes in total soil and biomass N, Ca, K, Mg, and P over 120 years from published data for a spruce-fir site in Maine, two northern hardwood sites in New Hampshire, central hardwood sites in Connecticut and Tennessee, and a loblolly pine site in Tennessee. For N, atmospheric inputs counterbalance the outputs, and there is little long-term change on most sites. For K, Mg, and P, the total pool may decrease by 2%–10% in 120 years depending on site and harvest intensity. For Ca, net leaching loss is 4–16 kg/ha/yr in mature forests, and whole-tree harvest removes 200–1100 kg/ha. Such leaching loss and harvest removal could reduce total soil and biomass Ca by 20%–60% in only 120 years. We estimated unmeasured Ca inputs from rock breakdown, root-zone deepening, and dry deposition; these should not be expected to make up the Ca deficit. Acid precipitation may be the cause of current high leaching of Ca. Although Ca deficiency does not generally occur now in acid forest soils, it seems likely if anthropogenic leaching and intensive harvest removal continue.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1432-1009
    Keywords: Acid precipitation ; Acidification ; New Hampshire ; Ponds ; Rock weathering ; Stream chemistry ; Streams ; White Mountains
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract The streams tributary to acidic Cone Pond, pH 4.5–4.8, and circumneutral Black Pond, pH 5.3–6.4, in the White Mountains of New Hampshire, USA, were monitored for a year. The watersheds of these two ponds were characterized in terms of geology and stream hydrology. Chemical gradients and patterns in rock weathering and groundwater discharge explain many of the differences in mineral content and acidity of the streams. The rocks of Black watershed produced an average of ten times the equivalent of basic cations as rocks from Cone watershed. This is on the same order as the difference in acidity of the two streams. Down-stream changes in stream chemistry follow differing patterns, but reflect the same principle of residence time and water path length controlling chemical evolution of streamwater. Watershed and aquatic managers may use these parameters in an inexpensive and simple assessment of the susceptibility of individual streams and ponds to acidification. A method is recommended to determine quickly the potential influence of bedrock type to aquatic chemistry.
    Type of Medium: Electronic Resource
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