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151.
152.
Kenneth Heber 《BMJ (Clinical research ed.)》1965,2(5467):943-944
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155.
Comparison of α1 -Adrenergic Receptor-Stimulated Inositol Phosphate Formation in Primary Neuronal and Glial Cultures 总被引:3,自引:3,他引:0
alpha 1-Adrenergic receptor binding sites and norepinephrine-stimulated 3H-inositol phosphate (3H-InsP) accumulation were measured in primary cultures of neurons and glia from 1-day-old rat brains. The density of alpha 1-adrenergic receptor binding sites was approximately three times higher in membranes from neurons compared to glia. Although norepinephrine was slightly more potent in stimulating 3H-InsP formation in neurons than in glia, the maximal response was greater in glial cells. Norepinephrine-stimulated 3H-InsP formation remained constant for [3H]inositol prelabelling periods of 1-14 days in neurons, whereas the response increased with time in glia and was maximal after 7-10 days of prelabelling. Both the incorporation of [3H]inositol into lipid and basal levels of 3H-InsPs were lower in glial cells than in neurons, which accounted for the greater percent stimulation in glia. Pretreatment with phenoxybenzamine decreased norepinephrine-stimulated 3H-InsP formation in a dose-dependent manner in both neurons and glia by decreasing the maximal response without altering potency. HPLC separation showed that similar types of 3H-InsPs were accumulated in neurons and glial cells. These results demonstrate that alpha 1-adrenergic receptors exist on both neurons and glial cells and activate 3H-InsP accumulation in both cell types. Although receptor density is higher in neurons than in glia, the 3H-InsP response is higher in glia. This difference does not appear to be due to different receptor reserves, but may be due to differential coupling mechanisms in the two cell types. 相似文献
156.
Summary The rate of synonymous nucleotide substitution in nuclear genes of higher plants has been estimated. The rate varies among genes by a factor of up to two, in a manner that is not immediately explicable in terms of base composition or codon usage bias. The average rate, in both monocots and dicots, is about four times higher than that in chloroplast genes. This leads to an estimated absolute silent substitution rate of 6 × 10–9 substitutions per site per year that falls within the range of average rates (2–8 × 10–9) seen in different mammalian nuclear genomes. 相似文献
157.
A Direct Screening Procedure for Gravitropism Mutants in Arabidopsis thaliana (L.) Heynh. 总被引:5,自引:5,他引:0
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Bertha L. Bullen Thérèse R. Best Mary M. Gregg Sara-Ellen Barsel Kenneth L. Poff 《Plant physiology》1990,93(2):525-531
In order to isolate gravitropism mutants of Arabidopsis thaliana (L.) Heynh. var Estland for the genetic dissection of the gravitropism pathway, a direct screening procedure has been developed in which mutants are selected on the basis of their gravitropic response. Variability in hypocotyl curvature was dependent on the germination time of each seed stock, resulting in the incorrect identification of several lines as gravitropism mutants when a standard protocol for the potentiation of germination was used. When the protocol was adjusted to allow for differences in germination time, these lines were eliminated from the collection. Out of the 60,000 M2 seedlings screened, 0.3 to 0.4% exhibited altered gravitropism. In approximately 40% of these mutant lines, only gravitropism by the root or the hypocotyl was altered, while the response of the other organ was unaffected. These data support the hypothesis that root and hypocotyl gravitropism are genetically separable. 相似文献
158.
Summary The effects of temperature, dissolved oxygen, and other environmental parameters under both aerobic and anaerobic conditions were investigated using one aerobic and one facultative strain isolated from wastewater treatment plant sludge. Among other results, we found that low dissolved oxygen levels and low temperatures decreased the rate of DEP degradation and the growth rate, and that the facultative strain was much less affected by the lower DO concentrations than the aerobic strain. 相似文献
159.
Ivan Valiela Joseph Costa Kenneth Foreman John M. Teal Brian Howes David Aubrey 《Biogeochemistry》1990,10(3):177-197
Anthropogenic activities on coastal watersheds increase nutrient concentrations of groundwater. As groundwater travels downslope it transports these nutrients toward the adjoining coastal water. The resulting nutrient loading rates can be significant because nutrient concentrations in coastal groundwaters may be several orders of magnitude greater than those of receiving coastal waters. Groundwater-borne nutrients are most subject to active biogeochemical transformations as they course through the upper 1 m or so of bottom sediments. There conditions favor anaerobic processes such as denitrification, as well as other mechanisms that either sequester or release nutrients. The relative importance of advective vs. regenerative pathways of nutrient supply may result in widely different rates of release of nutrients from sediments. The relative activity of denitrifiers also may alter the ratio of N to P released to overlying waters, and hence affect which nutrient limits growth of producers. The consequences of nutrient (particularly nitrate) loading include somewhat elevated nutrient concentrations in the watercolumn, increased growth of macroalgae and phytoplankton, reduction of seagrass beds, and reductions of the associated fauna. The decline in animals occurs because of habitat changes and because of the increased frequency of anoxic events prompted by the characteristically high respiration rates found in enriched waters. 相似文献
160.
Kenneth B. Armitage Jaye C. Melcher John M. Ward Jr 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1990,160(5):491-502
Summary Yellow-bellied marmots characteristically live in montane-mesic environments, but in several areas in western North America, this species extended its range into lowland-xeric habitats. Body mass was significantly smaller in the lowland-xeric population from eastern Washington at 393 m than in the montane-mesic population from western Colorado at 2900 m. Oxygen consumption of marmots from montane-mesic and lowland-xeric environments was signiflcantly affected by ambient temperature (TA) water regimen, population, and a population x water regimen x temperature interaction. Lowland-xeric animals had a higher metabolic rate at low TAs, but a lower metabolic rate at higher TAs than the montane-mesic aminals. Oxygen consumption was lower on a restricted-water regimen than on ad libitum water in both populations. Coefficients relating oxygen consumption to body mass were affected by TA, water regimen, and population. These intraspecific coefficients are larger than the interspecific coefficients for all mammals. Body temperature (TB) was affected significantly by TA, water regimen, and population. TA body mass, and a population x water regimen interaction significantly affected conductance. Conductance generally was higher in the lowland-xeric than in the montane-mesic marmots. Both populations increased conductance at high TA, but the lowland-xeric population dissipated a much higher proportion of the heat by evaporative water loss (EWL) than did the montane-mesic population. Metabolic water production exceeded or equaled EWL at 5–20°C. Smaller body size, reduced metabolism at high TA, and increased EWL at high TA characterized the lowland-xeric population.Metabolic rates of yellow-bellied marmots were higher than predicted from body size during the reproductive season but decreased to 67% of that predicted from the Kleiber curve by late summer. Marmots minimize thermoregulatory costs by concentrating activity at times when the microclimate is favorable, by tolerating hyperthermia at high TA in the field, and by having a conductance lower than that predicted from body size.Abbreviations
DHC
dry-heat conductance
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EHL
evaporative heat loss
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EWL
evaporative water loss
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HP
heat produced
-
T
A
ambient temperature
-
T
n
body temperature
-
M
body mass 相似文献