bluuebunny/crossref_metadata_2025_split huggingface dataset:
P‐glycoprotein phosphorylation/dephosphorylation and cellular accumulation of L‐DOPA in LLC‐GA5 Col300 cells
Authors: Sampaio‐Maia B. , Gomes R. , Soares‐da‐Silva P. 
Published: March 2003

1 The present work was aimed to study the effect of PKC activation and protein‐serine/threonine phosphatase (PP1/PP2 A) inhibition on P‐glycoprotein (P‐gp) mediated transport of L‐DOPA in LLC‐GA5 Col300 cells, a renal cell line expressing the human P‐glycoprotein in the apical membrane. 2 L‐DOPA accumulation was a time‐and concentration‐dependent process with the following kinetic characteristics: kin, 57.3 ± 1.2 pmol mg protein−1 min−1; kout, 3.3 ± 0.1 pmol mg−1 protein min−1; Amax, 10.6 ± 0.8; Km, 198 ± 64 μm; Vmax, 5.2 ± 0.7 nmol mg protein−1. 3 Verapamil (25 μm), a P‐glycoprotein inhibitor, markedly increased (≈ 40% increase) the accumulation of a non‐saturating concentration of L‐DOPA (2.5 μm) at both initial rate of uptake (IRU, 6 min incubation) and at steady‐state (SS, 30 min incubation). 4 PKC activation with phorbol 12,13‐dibutyrate (PDBu, 1, 3 and 10 n
m) produced a concentration‐dependent decrease in L‐DOPA accumulation at SS, but not at IRU. The inactive phorbol ester, 4α‐phorbol 12,13‐didecanoate (100 n
m), produced no change in L‐DOPA accumulation. The effect of PDBu was completely reverted by staurosporine (100 n
m). The phosphatase inhibitor okadaic acid (100 n
m) reduced by 20% the accumulation of L‐DOPA at IRU, but not at SS. 5 It is suggested that P‐glycoprotein plays a role in regulation of intracellular availability of L‐DOPA in renal epithelial cells, and phosphorylation/dephosphorylation of P‐glycoprotein may be involved in the regulation of the transporter.
Vascular actions of 17β‐oestradiol in rat aorta and mesenteric artery
Authors: Browne M. , Connolly C. , Docherty J. R. 
Published: March 2003

1 It has been proposed that the cardiovascular protective actions of 17β‐oestradiol may involve calcium antagonistic actions. We have examined the effects of 17β‐oestradiol on contractions to noradrenaline and KCl in male rat small mesenteric artery and aorta. 2 In rat mesenteric artery, 17β‐oestradiol (10 μm) significantly reduced the maximum contraction to noradrenaline (67.7 ± 5.8% of control) and KCl (38.8 ± 3.1% of control) without affecting potency. 3 In rat aorta, 17β‐oestradiol (10 μm) also significantly reduced contractions to noradrenaline (77.5 ± 4.8% of control), and the effects were mimicked by droloxifene (10 μm). The effect of oestrogen was not prevented by the protein synthesis inhibitor cycloheximide (10 μm). In experiments carried out in calcium‐free solution in which calcium stores were depleted, 17β‐oestradiol (10 μm) significantly reduced the contraction to calcium restoration in rat aorta. 4 In aorta from female rats, 17β‐oestradiol (10 μm) significantly reduced contractions to noradrenaline (73.6 ± 10.8% of control), but this effect of oestrogen was not prevented by cycloheximide (10 μm). 5 In summary, 17β‐oestradiol diminishes the maximum contractile response to noradrenaline in both rat small mesenteric artery and aorta, an effect which at least in the aorta is mimicked by the oestrogen receptor antagonist/partial agonist droloxifene, and may be due to restriction of calcium entry by a nongenomic action.
Activation of presynaptic A1‐receptors by endogenous adenosine inhibits acetylcholine release in the guinea‐pig ileum
Authors: Lee J. J. , Talubmook C. , Parsons M. E. 
Published: March 2003

1 It is well established that presynaptic adenosine A1‐receptor activation inhibits acetylcholine (ACh) release in the guinea‐pig ileum. The present study extends this observation and examines a possible role for endogenous adenosine in modulating cholinergic nerve function. 2 The actions of the adenosine uptake blocker, dipyridamole, the adenosine deaminase inhibitor, erythro‐9(2‐hydroxy‐3‐nonyl)adenine (EHNA) and the A1‐receptor antagonist, 1,3‐dipropyl‐8‐cyclopentylxanthine (DPCPX) were examined on electrically evoked neurogenic, cholinergic twitch contractions of the guinea‐pig ileum. Some additional studies measuring [3H]‐ACh release were also performed. 3 Adenosine and the selective A1‐receptor agonist, 2‐chloroadenosine (2‐CA), inhibited electrically evoked contractions and, in the case of 2‐CA, [3H]‐ACh release. The actions were antagonized by DPCPX. At low concentrations, dipyridamole and EHNA enhanced the effect of adenosine causing a leftward shift of the concentration–response curve. In contrast, inhibition induced by 2‐CA was unaffected by either dipyridamole or EHNA. 4 When applied alone at higher concentrations, EHNA and dipyridamole produced a concentration‐dependent suppression of cholinergic neurotransmission. In both cases, the effect could be reversed by DPCPX. At the same concentration, DPCPX alone produced a small but consistent increase in twitch height and [3H]‐ACh release. 5 The data confirm the existence of inhibitory presynaptic adenosine A1‐receptors modulating cholinergic nerve function in the guinea‐pig ileum and suggests that these receptors can be activated by endogenous adenosine released either as adenosine itself or as an ATP metabolite.
A numerical analysis of the mesoscale distribution patterns of vascular plants in the subarctic Kevo Nature Reserve, northern Finland
Authors: Heikkinen Risto , Birks H. J. B , Kalliola Risto 
Published: March 2003

Different numerical techniques were used to detect and describe the major ecological‐biogeographical patterns of vascular plant distributions at the meso‐scale level in a subarctic region in Finland. The distribution patterns of 231 native taxa in 362 1 km2 grid squares of the Kevo Nature Reserve were analysed by two‐way indicator species analysis and detrended correspondence analysis, and were subsequently related to twenty‐eight geographical, topographical, geological, and vegetational variables using simple discriminant functions and canonical correspondence analysis with associated Monte Carlo permutation tests.The floristic variation detected reflects variations in environmental factors operative at the regional and local scales. No major broad‐scale coherent geographical patterns were detected; instead, the spatial distribution of the grids with a similar floristic composition shows a scattered distribution. All the numerical techniques reveal a major gradient from alpine areas to lowland sites with rivers and rocky outcrops, and the most important explanatory variables for predicting the main floristic variation are all associated with altitude. The floristic patterns represented by the second ordination gradient mainly correlate with the abundance of mires. Partial ordinations indicate that both the geographical and geological variables explain relatively little of the species distributional patterns.Although the meso‐scale approach reveals much about the plant‐environment relationships in the study area, the floristic variation appears to be determined mainly by fine‐scale factors. In the most heterogeneous grids, the grid size used fails to detect accurately the ecological patterns of the species present.
Oaks, acorns, and the geographical ecology of acorn woodpeckers
Authors: Koenig Walter D. , Haydock Joseph 
Published: March 2003

SummaryWe investigated the geographical ecology of acorn woodpeckers (Melanerpes formicivorus) using 30 years of Audubon Christmas Bird Counts and data on the diversity and abundance of oaks. Spatial autocorrelation in acorn woodpecker population densities is not significantly greater than zero both in either the southwestern United States, where populations are often locally isolated, or along the Pacific Coast, where they are more evenly distributed. In both regions, the effective distributional limit of acorn woodpeckers is set not by the limits of oaks but by sites where oak diversity drops to a single species. This result is consistent with acorn production patterns in central coastal California demonstrating that variability in overall acorn production and the probability of acorn crop failure decline with increasing oak species number but drop most markedly when two, compared to one, species of oaks are present together. Along the Pacific Coast, acorn woodpecker densities increase and population variability decreases with increasing abundance and diversity of oaks; however, analyses indicate that overall population size in this region is primarily determined by resource abundance while population stability is determined by resource diversity. Comparable patterns are not obvious in the Southwest, where acorn woodpecker densities are much lower than along the Pacific Coast. This may be due to a combination of greater competition for resources and oak communities that differ both qualitatively and quantitatively in their productivity compared to those along the Pacific Coast.
Effects of data characteristics on the results of reserve selection algorithms
Authors: Pressey R. L. , Possingham H. P. , Logan V. S. , Day J. R. , Williams P. H. 
Published: March 2003

SummaryWe tested the effects of four data characteristics on the results of reserve selection algorithms. The data characteristics were nestedness of features (land types in this case), rarity of features, size variation of sites (potential reserves) and size of data sets (numbers of sites and features). We manipulated data sets to produce three levels, with replication, of each of these data characteristics while holding the other three characteristics constant. We then used an optimizing algorithm and three heuristic algorithms to select sites to solve several reservation problems. We measured efficiency as the number or total area of selected sites, indicating the relative cost of a reserve system. Higher nestedness increased the efficiency of all algorithms (reduced the total cost of new reserves). Higher rarity reduced the efficiency of all algorithms (increased the total cost of new reserves). More variation in site size increased the efficiency of all algorithms expressed in terms of total area of selected sites. We measured the suboptimality of heuristic algorithms as the percentage increase of their results over optimal (minimum possible) results. Suboptimality is a measure of the reliability of heuristics as indicative costing analyses. Higher rarity reduced the suboptimality of heuristics (increased their reliability) and there is some evidence that more size variation did the same for the total area of selected sites. We discuss the implications of these results for the use of reserve selection algorithms as indicative and real‐world planning tools.
Mid‐Holocene vegetation diversity in eastern Cumbria
Authors: Skinner C. , Brown A. G. 
Published: March 2003

SummaryThe concept of biodiversity can operate at several different ecological levels from that of the Global ecosystem to the genetic diversity of a single species. This paper focuses on the beta‐type diversity of vegetation communities at the intra and inter‐regional scale, using five mid‐Holocene (Neolithic) pollen diagrams from eastern Cumbria (c. 500 km2 centred on the Eden valley). The sites were selected in order to include the variation in both soil/rock type and altitude within the study area, ranging from the Eden valley and southern limestone plateau to the foothills and summits of the western edge of the Pennines. The local pollen component which is dominant in these small sites, is used to determine intra‐regional vegetation diversity for a time‐slice in the Neolithic. Simple statistical methods are used to compare sites and as a measure of intra‐regional vegetation‐type diversity. This is compared with estimates of the community diversity for the British Isles during the same period. The results suggest that the intra‐regional vegetation diversity is comparable to that of Northern England, and it is related to variation in both altitude and soil type. There are some differences, for example the steepness of the western face of the Pennines is probably responsible for a lack of the pine dominated zone, and pedological constraints probably prevented the full development of woodland on the limestone plateau at the south of the study area. The open landscape of the limestone plateau acted as a refuge for late glacial herbaceous taxa prior to their re‐expansion into the wider landscape after widespread deforestation and arable cultivation. The results have implications for both the mapping of past vegetation at the national scale and for landscape archaeology.
Altitudinal and latitudinal distribution of east Malagasy forest bird communities
Authors: Hawkins A. F. A. 
Published: March 2003

Summary Aim To describe variation in forest bird communities with altitude and latitude. Location Eastern Madagascar. Methods Extraction of data from forest bird inventories conducted in eastern Madagascar. Results There is a strong decline in species richness with altitude, above about 1300 m. Below this altitude, species richness is about constant or declines slightly. Seventy‐eight percent of species occurring regularly in forest are absent from at least one of low, mid‐altitude or high altitude forest. Of eighty‐seven species occurring regularly in forest, only four or possibly five have latitudinally limited distributions, over a latitudinal range of over 1200 km. Three or possibly four are limited to the northern two‐thirds, and one appears to be at least much more common in the southern half. Main conclusions Eastern Malagasy rain forest birds show previously unanalysed variation in altitudinal distribution. There is much less latitudinal variation. Species currently considered threatened are concentrated in the lowland and high‐altitude zones. This may be at least partly due to lack of survey effort giving the impression that these species are rare, but lowland forests at least are under great human pressure. Bird conservation initiatives would probably have most effect if targeted at lowland east Malagasy rain forest.
Habitat associations of parrots on the Wallacean islands of Buru, Seram and Sumba
Authors: Marsden Stuart , Fielding Alan 
Published: March 2003

Summary Aim To investigate patterns of habitat use in nineteen populations of parrots on three Wallacean islands, and examine the degree to which habitats used by a species can be predicted across islands. Location The Wallacean islands on Buru, Seram and Sumba. Methods A logistic regression method was used to relate the presence/absence of parrot species at census plots to vegetation axes derived from ‘gross’ habitat parameters such as altitude, tree sizes, and percentages of vegetation coverage at different strata. Receiver Operating Characteristic Plots were then used to test predictions of habitat use by conspecific populations on the nearby and distant islands, and by different parrot species on the same island. Results Parrots on Buru and nearby Seram tended to be associated with open‐canopied lowland forests, while on the distant and low‐lying island of Sumba, the preference was for closed‐canopy forests at higher altitudes. There were usually close affinities in habitat usage by conspecific populations on the two nearby islands. One exception was where the species occurred on the two islands as separate subspecies. Habitat preferences on Sumba, however, were so distinct that paradigms developed for Buru and Seram failed to predict distributions on this distant island. Main conclusions For populations on more distant islands, it will usually be better to predict habitat use by considering the habitat used by other parrot species occurring on that island, than a conspecific population from another region. Conservation research programmes which concentrate parrot study on just one or two islands in every region of Wallacea may be more successful than those which ‘run through’ several islands in a group, but which miss out whole regions.
Brazilian Páramos I. An introduction to the physical environment and vegetation of the campos de altitude
Authors: DeForest Safford Hugh 
Published: March 2003

Summary Aim The campos de altitude are a series of cool‐humid, grass‐dominated formations restricted to the highest summits of the southeastern Brazilian Highlands. Relatively little is known of the ecology, biogeography, or developmental history of this archipelago of mountaintop formations. This contribution presents an overview of our present state of knowledge with respect to the past and present physical environment and vegetation of the campos de altitude. The aim is (1) to introduce an international audience to the natural history of these diminutive yet important ecosystems, and (2) to provide the background for a series of forthcoming contributions that will treat the ecology of the campos de altitude and explore physical and biotic relationships between these ‘Brazilian páramos’ and similar formations in the high mountains of equatorial South and Central America. Location Beginning at altitudes of 1800–2000 m, the campos de altitude are found atop the highest summits of the main ranges of the southeastern Brazilian Highlands, between the states of Santa Catarina and Minas Gerais/Espírito Santo. Methods Drawing upon both original data and previously published results, this contribution reviews what we presently know about the physical environment and vegetation of the campos de altitude, in the context of geographic setting, geology, palaeoclimatology and palaeobotany, modern climate, modern vegetation, and conservation. Results and main conclusions Uplift of the southeastern Brazilian ranges to altitudes high enough to support orographic grasslands may have occurred as early as the middle‐ to late‐Tertiary; pollen records show that campos de altitude have been extant on southeastern summits at least since the Late Pleistocene. The present‐day climate of the campos de altitude is cool and (per)humid, but patterns of rainfall, temperature, and frost are distinctly seasonal. Although the flora of the campos de altitude is highly diverse and characterized by a high degree of endemism, the campos de altitude maintain strong floristic similarities to equatorial alpine formations of the Andean and Central American Cordillera; these similarities also extend to climate, soils, and vegetation physiognomy. Anthropogenic fires and grazing are widespread in the campos de altitude and probably contribute significantly to the modern structure of vegetation communities.
Distribution and ecology of myxomycetes in high‐latitude regions of the Northern Hemisphere
Authors: Stephenson Steven L. , Novozhilov Yuri K. , Schnittler Martin 
Published: March 2003

AbstractAimThe objective of this study was to analyse the data represented by 1976 specimens of myxomycetes collected in high‐latitude regions of the Northern Hemisphere to obtain information on the biogeographical relationships and patterns of occurrence of these organisms. The question of what factors limit myxomycete distribution in high‐latitude and cold‐dominated regions was also addressed.LocationSpecimens of myxomycetes considered herein were collected from twelve study areas in Iceland, northern Russia and Alaska, and Greenland. The vast majority of specimens were collected during the period of 1989–98.MethodsNine hundred and thirty‐three specimens were recorded as field collections. In addition, 1043 specimens originated from moist chamber cultures prepared with 1453 substratum samples collected in the various study areas. From a database recording the type of substratum (wood, bark of living trees, litter or dung) for each specimen, patterns of substratum occurrence for particular species of myxomycetes in high‐latitude regions were determined.ResultsFrom the 150 species recorded for the twelve study areas, thirty‐three were found to be widely distributed (recorded from at least five study areas), and only forty‐one had a frequency of occurrence higher than 1% either in moist chambers or as field collections. These data were examined in an effort to identify possible factors limiting the distribution of myxomycetes in high‐latitude regions.Main conclusionsUpon first inspection, the arctic and subArctic myxomycete biota seems to be a depauperate version of that of temperate and boreal regions. However, a few species elsewhere recorded as rare but found to be fairly common in this study indicate that a certain degree of distinctiveness exists in Arctic and subArctic myxomycetes.
Explanations of patterns of intertidal diversity at regional scales
Authors: Zacharias Mark A. , Roff John C. 
Published: March 2003

AimTo test the hypothesis that the abiotic variables of salinity, temperature and fetch could explain patterns of intertidal species richness at regional scales (100–1000 s of km).LocationBritish Columbia, Canada.MethodsUsing a 180 station data set collected over 7° of latitude on bedrock shorelines, we used a combination of correlation, multiple regression and ordination to show that species richness was strongly related to fetch, salinity and temperature.ResultsResults are consistent with the expected outcomes from the stability‐time and intermediate disturbance hypotheses.Main conclusionsTemperate intertidal environments are predominantly physically accomodated at regional scales. Implications for near‐shore conservation are that the conservation of outer coast environments protects more species in a given area than inner coast environments.
Spatial and temporal variation of fire regimes in a mixed conifer forest landscape, Southern Cascades, California, USA
Authors: Beaty R. Matthew , Taylor Alan H. 
Published: March 2003

AimIn this study, we evaluated the fire‐forest mosaic of a mixed conifer forest landscape by testing the hypothesis that pre‐fire suppression fire regime parameters vary with species composition (tree species), and environment (i.e. slope aspect, slope position, elevation).LocationOur study was conducted in the 1587 ha Cub Creek Research Natural Area (CCRNA), Lassen National Forest, CA, USA.MethodsWe quantified the return interval, seasonal occurrence, size, rotation period, and severity of fires using dendroecology.ResultsSlope aspect, potential soil moisture, forest composition, and fire regime parameters in our study area co‐vary. Median composite and point fire return intervals (FRI) were longest on higher, cooler, more mesic, north‐facing (NF) slopes covered with white fir (Abies concolor), Douglas fir (Pseudotsuga menziesii)–white fir, and red fir (A. magnifica)–white fir forests, shortest on the dry, south‐facing (SF) slopes covered with ponderosa pine (Pinus ponderosa)–white fir forests and intermediate on west‐facing slopes dominated by white fir–sugar pine (P. lambertiana)–incense cedar (Libocedrus decurrens) forests. The spatial pattern for length of fire rotation (FR) was the same as that for FRI. Fires in CCRNA mixed conifer forests occurred mainly (90%) in the dormant season. Size of burns in CCRNA mixed conifer forests were generally small (mean=106 ha), however, during certain drought years widespread fires burned across fuel breaks and spread throughout the watershed. Fire severity was mainly high on upper slopes, low on lower slopes and moderate and low severity on middle slopes. Patterns of fire severity also varied with slope aspect. Fire frequency decreased dramatically in CCRNA after 1905.ConclusionsIn CCRNA, fire regime parameters [e.g. FRI, fire extent, FR, fire severity] varied widely with species composition, slope aspect and slope position. There was also temporal variation in fire extent with the most widespread fires occurring during drought years. The important contributions of topography and climate to variation in the fire regime indicates that exogenous factors play a key role in shaping the fire‐forest structure mosaic and that the fire‐forest structure mosaic is more variable, less predictable and less stable than previously thought. Finally, some characteristics of the fire regime (i.e. fire severity, season of burn) in CCRNA are different than those described for other mixed conifer forests and this suggests that there are geographical differences in mixed conifer fire regimes along the Pacific slope.