Calcium diffusion in transient and steady states in muscle.

Rates of diffusion through the extracellular space of thin sheets of myocardium from the right ventricular outflow tract of kittens were estimated at 23 degrees C for 45Ca2+ and an inert reference tracer, [14C]sucrose. The myocardial sheets were mounted in an Ussing chamber and equilibrated with Tyrode solution with varied calcium concentrations, Cao. The tracers were added to one side and their concentrations on the other side measured at 5-15-min intervals for 6 h. The apparent tracer diffusion coefficient for sucrose was 1.11 +/- 0.06 X 10(-6) cm2s-1 (mean +/- SEM, n = 74), 22% of the free diffusion coefficient; the lag time before reaching a steady state provided estimates of the intratissue volume of distribution or diffusion space of 0.41 +/- 0.15 ml/ml tissue (n = 74), a value compatible with expectations for extracellular fluid space. Over the range of Cao from 0.02 to 9.0 mM, the intratissue apparent diffusion coefficient for Ca, DCa, averaged 1.65 +/- 0.10 X 10(-6) cm2s-1, n = 74, which is 21% of the free DoCa, and was not influenced by Cao. Because transsarcolemmal Ca permeation is slow, DCa is the diffusion coefficient in the extracellular region. The paired ratios DCa/Ds averaged 1.32 +/- 0.05 (n = 67) for all levels of Cao but at physiologic or higher Cao averaged 1.45 +/- 0.07 (n = 39), close to the ratio of free diffusion coefficients, 1.53. Equations distinguishing transient from steady state diffusion were fitted to the data, showing that the apparent distribution volume of "binding sites" external to the diffusion pathway diminished at higher Cao in a fashion suggesting that a least two different Ca2+ binding sites were present.     

Biomass and elemental uptake in fertilized and unfertilizedBetula papyrifera Marsh. andPopulus grandidentata Michx.

Summary Estimates were made of the above-ground biomass and contents of N, P, K, Ca, Mg, Mn, Na, Fe, Zn, Al, and Cu in fertilized (N 448 kg/ha, P 112 kg/ha, lime 4480 kg/ha) and unfertilized white birch (Betula papyrifera Marsh.) and bigtooth aspen (Populus grandidentata Michx.). For individuals of both species, fertilization increased the average above-ground biomass increment and the N and P content increment by 150 per cent and 300 per cent, respectively, but decreased uptake of Mn and Zn. The allocation of biomass and elements differs not only between species, but within species under untreated and fertilized conditions.     

Conversion of lipids to fatty alcohols and lysolipids by NaBH4

A variety of fatty acid esters were reacted with NaBH₄ in tetra-hydrofuran (THF) — water mixtures. Although triglycerides and free acids were stable under the conditions employed, more polar lipids were extensively reduced to the corresponding fatty alcohols. Thus when reacted with NaBH₄ for 60 min at 37°C, 94% and 64% respectively of the acyl groups in lecithin and monogalactosyl diglyceride were reduced to fatty alcohols. No discernible reduction or isomerisation of double bonds occurred during the reactions. Reductions in the reaction temperature, and in the THF content of the solvent, both resulted in slower reaction rates.The reactions with complex lipids proceded with the intermediate formation of the corresponding monoacyl (“lyso”) lipids, but the reagent showed no selectivity towards position or structure of the component ester groups.In its proposed form, the method for determining acyl thiolesters in biological tissues by their specific reduction with NaBH₄, is not satisfactory.     

Multi-temporal ecological analysis of Jeffrey pine beetle outbreak dynamics within the Lake Tahoe Basin

From 1991 to 1996, Jeffrey pine beetles (Dendroctonus jeffreyi Hopkins) (JPB) caused tree mortality throughout the Lake Tahoe Basin during a severe drought. Census data were collected annually on 10,721 trees to assess patterns of JPB-caused mortality. This represents the most extensive tree-level, spatiotemporal dataset collected to-date documenting bark beetle activity. Our study was an exploratory assessment of characteristics associated with the probability of successful JPB mass-attack (P_JPB) and group aggregation behavior that occurred throughout various outbreak phases. Numerous characteristics associated with P_JPB varied by outbreak phase although population pressure and forest density had positive associations during all phases. During the incipient phase, JPBs caused mortality in individual trees and small groups within toeslope topographic positions and P_JPB had a negative relationship with stem diameter. In the epidemic phase, JPB activity occurred in all topographic positions and caused mortality in spatially expanding clusters. P_JPB had a curvilinear relationship with tree diameter and a negative relationship with proximity to nearest brood tree. Majority (92–96 %) of mass-attacked trees were within 30 m of a brood tree during the peak epidemic years. During the post-epidemic phase, mortality clusters progressively decreased while dispersal distances between mass-attacked and brood trees increased. Post-epidemic P_JPB had a negative relationship with stem diameter and mortality was concentrated in the mid and upper-slope topographic positions. Results indicate mortality predictions are reasonable for the epidemic phase but not for incipient and post-epidemic phases. Ecological factors influencing JPB-caused tree mortality, clustered mortality patterns, and transitions from environmental to dynamic determinism are discussed.     

Species pools and the "hump-back" model of plant species diversity: an empirical analysis at a relevant spatial scale

We investigated the relative roles of productivity, the species pool, and spatial habitat structure in determining local species richness (alpha diversity) of plant communities within a single, well-defined landscape unit, at spatial and ecological scales where the relationship between community productivity and species diversity often assumes a unimodal or "hump-back" form. At high levels of productivity, the decrease-phase of the unimodal model of the diversity-productivity relationship is typically explained as the dynamic outcome of increased competitive exclusion, but it may also be the passive consequence of a small pool of species possessing attributes necessary to competitively survive in high-fertility environments. We conducted statistical analyses of previously collected data to determine whether variations in local richness in the herbaceous vegetation of a Slovakian mountain valley were best explained by habitat productivity itself (which presumably leads to more intense competition) or by the sizes of the relevant community species pools. We also used measures of spatial habitat structure to investigate the extent to which habitat patchiness influenced patterns of species diversity. In the study system, both community biomass and size of the species pools contributed significantly to local species richness, but the positive effect of the species pools was about twice as important as the negative effect of biomass. The combined area of related associations (alliance area), association perimeter, and habitat patch geometry were all closely related to species pool size.     

The delivery of evidence-based preventive care for older Americans with arthritis

Introduction  

Previous research suggests patients with rheumatoid arthritis (RA) may receive suboptimal care with respect to preventive tests and services. We evaluated the proportion of older Americans with RA, psoriatic arthritis (PsA), and osteoarthritis (OA) receiving these services and the specialty of the providers delivering this care.     

Aspen (<Emphasis Type="Italic">Populus tremuloides</Emphasis>) stands and their contribution to plant diversity in a semiarid coniferous landscape

We conducted a field study to determine the relative contributions of aspen (Populus tremuloides), meadow, and conifer communities to local and landscape-level plant species diversity in the Sierra Nevada and southern Cascade Range, northeastern California, USA. We surveyed plant assemblages at 30 sites that included adjacent aspen, conifer, and meadow communities across a 10,000-km² region. We statistically investigated patterns in local and landscape-scale plant diversity within and among the three vegetation types. Summing across sites, aspen stands supported more plant species overall and more unique plant species than either meadow or conifer communities. Local richness and diversity did not differ between aspen and meadow plots; conifer forest plots were significantly lower in both measures. Heterogeneity in species composition was higher for aspen forest than for meadows or conifer forest, both within sites and between sites. Plant communities in aspen stands shared less than 25% of their species with adjacent vegetation in conifer and meadow plots. Within aspen forest, we found a negative relationship between total canopy cover and plant diversity. Our results strongly support the idea that plant communities of aspen stands are compositionally distinct from adjacent meadows and conifer forest, and that aspen forests are a major contributor to plant species diversity in the study region. Current patterns of aspen stand succession to conifer forest on many sites in the semiarid western US are likely to reduce local and landscape-level plant species diversity, and may also have negative effects on other ecosystem functions and services provided by aspen forest.     

Derivation and preliminary validation of an administrative claims-based algorithm for the effectiveness of medications for rheumatoid arthritis

Introduction

Administrative claims data have not commonly been used to study the clinical effectiveness of medications for rheumatoid arthritis (RA) because of the lack of a validated algorithm for this outcome. We created and tested a claims-based algorithm to serve as a proxy for the clinical effectiveness of RA medications.

Methods

We linked Veterans Health Administration (VHA) medical and pharmacy claims for RA patients participating in the longitudinal Department of Veterans Affairs (VA) RA registry (VARA). Among individuals for whom treatment with a new biologic agent or nonbiologic disease-modifying agent in rheumatic disease (DMARD) was being initiated and with registry follow-up at 1 year, VARA and administrative data were used to create a gold standard for the claims-based effectiveness algorithm. The gold standard outcome was low disease activity (LDA) (Disease Activity Score using 28 joint counts (DAS28) ≤ 3.2) or improvement in DAS28 by > 1.2 units at 12 ± 2 months, with high adherence to therapy. The claims-based effectiveness algorithm incorporated biologic dose escalation or switching, addition of new disease-modifying agents, increase in oral glucocorticoid use and dose as well as parenteral glucocorticoid injections.

Results

Among 1,397 patients, we identified 305 eligible biologic or DMARD treatment episodes in 269 unique individuals. The patients were primarily men (94%) with a mean (± SD) age of 62 ± 10 years. At 1 year, 27% of treatment episodes achieved the effectiveness gold standard. The performance characteristics of the effectiveness algorithm were as follows: positive predictive value, 76% (95% confidence interval (95% CI) = 71% to 81%); negative predictive value, 90% (95% CI = 88% to 92%); sensitivity, 72% (95% CI = 67% to 77%); and specificity, 91% (95% CI = 89% to 93%).

Conclusions

Administrative claims data may be useful in evaluating the effectiveness of medications for RA. Further validation of this effectiveness algorithm will be useful in assessing its generalizability and performance in other populations.     

Altered fire regimes cause long‐term lichen diversity losses

Many global ecosystems have undergone shifts in fire regimes in recent decades, such as changes in fire size, frequency, and/or severity. Recent research shows that increases in fire size, frequency, and severity can lead to long‐persisting deforestation, but the consequences of shifting fire regimes for biodiversity of other vegetative organisms (such as understory plants, fungi, and lichens) remain poorly understood. Understanding lichen responses to wildfire is particularly important because lichens play crucial roles in nutrient cycling and supporting wildlife in many ecosystems. Lichen responses to fire have been little studied, and most previous research has been limited to small geographic areas (e.g. studies of a single fire), making it difficult to establish generalizable patterns. To investigate long‐term effects of fire severity on lichen communities, we sampled epiphytic lichen communities in 104 study plots across California's greater Sierra Nevada region in areas that burned in five wildfires, ranging from 4 to 16 years prior to sampling. The conifer forest ecosystems we studied have undergone a notable increase in fire severity in recent decades, and we sample across the full gradient of fire severity to infer how shifting fire regimes may influence landscape‐level biodiversity. We find that low‐severity fire has little to no effect on lichen communities. Areas that burned at moderate and high severities, however, have significantly and progressively lower lichen richness and abundance. Importantly, we observe very little postfire lichen recolonization on burned substrates even more than 15 years after fire. Our multivariate model suggests that the hotter, drier microclimates that occur after fire removes forest canopies may prevent lichen reestablishment, meaning that lichens are not likely to recolonize until mature trees regenerate. These findings suggest that altered fire regimes may cause broad and long‐persisting landscape‐scale biodiversity losses that could ultimately impact multiple trophic levels.