Serum stimulation of phosphate uptake into 3T3 cells.

The stimulation by calf serum of phosphate uptake into 3T3 cells results from a change in maximum velocity of the transport process with no change in the Michaelis constant. Only arsenate among a series of inorganic structural analogs of phosphate inhibited phosphate uptake indicating a high specificity for the process. The arsenate inhibition was competitive in nature. Papaverine, theophylline, and protaglandin E1, drugs known to maintain high intracellular levels of cAMP, had little effect on serum stimulated phosphate uptake. The phosphate uptake stimulating factor(s) in serum could be distinguised from the 3T3 cell survival and migration factors by stability characteristics, but this factor(s) could not be completely separated from a uridine uptake stimulation activity or growth promoting activity using a variety of serum fractionation procedures. Only partial stimulation of the uptake process was achieved with any one serum fraction indicating a multiplicity of serum components is probably involved in this process. Because of the rapidity of serum activation of phosphate uptake and its apparent independence of intracellular cyclic nucleotide levels, it is suggested that serum factors may stimulate phosphate uptake by inducing structural changes in the phosphate carrier system.     

The effect of spatial heterogeneity on the persistence of predator-prey interactions

The effect of spatially discontinuous environments on predator-prey systems is examined by using a computer simulation model. It is shown that increasing prey dispersal and decreasing predator dispersal do not necessarily have a stabilizing influence on the interaction, as had been concluded by previous workers. The stability of predator-prey interaction depends on the interaction of the dispersal process with normal reproduction and feeding of the predator and prey species.     

Natural habitat change, commercial fishing, climate, and dispersal interact to restructure an Alaskan fish metacommunity

The metacommunity concept has recently been described to account for the roles of dispersal in regulating community structure. Despite its strong theoretical basis, there exist few large-scale and long-term examples of its applicability in aquatic ecosystems. In this study we used a long-term dataset (1961–2007) on the relative abundances of the dominant limnetic fishes from two interconnected lakes to investigate the synergistic effects of naturally declining lake volume (approximately 50% in 50 years), climate variation, fishery management, and dispersal on community composition. We found a marked shift in fish community composition and variability during a period of rapid natural habitat change; however, the change was most apparent in the downstream, more stable lake of the system rather than at the site of disturbance. Multivariate analysis suggested significant shifts in community composition and variability in the downstream lake. Results indicated that the community composition in both lakes was best explained by habitat loss in the upper watershed and the number of spawning adult sockeye salmon the previous year (reflecting both natural processes and commercial fishing). Furthermore, communities exhibited site-specific responses to climatic conditions (e.g., index of the Pacific Decadal Oscillation), whereby the upper lake responded to climate within a given year and with a 1-year time lag, whereas the downstream community responded only with a 1-year lag. We attribute this difference largely to downstream dispersal and recruitment of fish from the upper lake. Thus, we suggest that the interconnected nature of the communities in this system provides a useful and large-scale example of the metacommunity concept, whereby the effects of environmental disturbance on community structure ultimately depend on the effects of these disturbances on dispersal among ecosystems.     

Programmatic Cost Evaluation of Nontargeted Opt-Out Rapid HIV Screening in the Emergency Department

Background

The Centers for Disease Control and Prevention recommends nontargeted opt-out HIV screening in healthcare settings. Cost effectiveness is critical when considering potential screening methods. Our goal was to compare programmatic costs of nontargeted opt-out rapid HIV screening with physician-directed diagnostic rapid HIV testing in an urban emergency department (ED) as part of the Denver ED HIV Opt-Out Trial.

Methods

This was a prospective cohort study nested in a larger quasi-experiment. Over 16 months, nontargeted rapid HIV screening (intervention) and diagnostic rapid HIV testing (control) were alternated in 4-month time blocks. During the intervention phase, patients were offered HIV testing using an opt-out approach during registration; during the control phase, physicians used a diagnostic approach to offer HIV testing to patients. Each method was fully integrated into ED operations. Direct program costs were determined using the perspective of the ED. Time-motion methodology was used to estimate personnel activity costs. Costs per patient newly-diagnosed with HIV infection by intervention phase, and incremental cost effectiveness ratios were calculated.

Results

During the intervention phase, 28,043 eligible patients were included, 6,933 (25%) completed testing, and 15 (0.2%, 95% CI: 0.1%–0.4%) were newly-diagnosed with HIV infection. During the control phase, 29,925 eligible patients were included, 243 (0.8%) completed testing, and 4 (1.7%, 95% CI: 0.4%–4.2%) were newly-diagnosed with HIV infection. Total annualized costs for nontargeted screening were $148,997, whereas total annualized costs for diagnostic HIV testing were $31,355. The average costs per HIV diagnosis were $9,932 and $7,839, respectively. Nontargeted HIV screening identified 11 more HIV infections at an incremental cost of $10,693 per additional infection.

Conclusions

Compared to diagnostic testing, nontargeted HIV screening was more costly but identified more HIV infections. More effective and less costly testing strategies may be required to improve the identification of patients with undiagnosed HIV infection in the ED.     

Indicators of AEI applied to the Delaware Estuary

We evaluated the impacts of entrainment and impingement at the Salem Generating Station on fish populations and communities in the Delaware Estuary. In the absence of an agreed-upon regulatory definition of "adverse environmental impact" (AEI), we developed three independent benchmarks of AEI based on observed or predicted changes that could threaten the sustainability of a population or the integrity of a community. Our benchmarks of AEI included: (1) disruption of the balanced indigenous community of fish in the vicinity of Salem (the "BIC" analysis); (2) a continued downward trend in the abundance of one or more susceptible fish species (the "Trends" analysis); and (3) occurrence of entrainment/impingement mortality sufficient, in combination with fishing mortality, to jeopardize the future sustainability of one or more populations (the "Stock Jeopardy" analysis). The BIC analysis utilized nearly 30 years of species presence/absence data collected in the immediate vicinity of Salem. The Trends analysis examined three independent data sets that document trends in the abundance of juvenile fish throughout the estuary over the past 20 years. The Stock Jeopardy analysis used two different assessment models to quantify potential long-term impacts of entrainment and impingement on susceptible fish populations. For one of these models, the compensatory capacities of the modeled species were quantified through meta-analysis of spawner-recruit data available for several hundred fish stocks. All three analyses indicated that the fish populations and communities of the Delaware Estuary are healthy and show no evidence of an adverse impact due to Salem. Although the specific models and analyses used at Salem are not applicable to every facility, we believe that a weight of evidence approach that evaluates multiple benchmarks of AEI using both retrospective and predictive methods is the best approach for assessing entrainment and impingement impacts at existing facilities.     

Self-sustaining populations, population sinks or aggregates of strays: chum (Oncorhynchus keta) and Chinook salmon (Oncorhynchus tshawytscha) in the Wood River system, Alaska

Small populations can provide insights into ecological and evolutionary aspects of species distributions over space and time. In the Wood River system in Alaska, USA, small aggregates of Chinook (Oncorhynchus tshawytscha) and chum salmon (O. keta) spawn in an area dominated by sockeye salmon (O. nerka). Our objective was to determine whether these Chinook and chum salmon are reproductively isolated, self-sustaining populations, population sinks that produce returning adults but receive immigration, or strays from other systems that do not produce returning adults. DNA samples collected from adult chum salmon from 16 streams and Chinook salmon from four streams in the Wood River system over 3 years were compared to samples from large populations in the nearby Nushagak River system, a likely source of strays. For both species, microsatellite markers indicated no significant genetic differentiation between the two systems. Simulations of microsatellite data in a large source and a smaller sink population suggested that considerable immigration would be required to counteract the diverging effects of genetic drift and produce genetic distances as small as those observed, considering the small census sizes of the two species in the Wood River system. Thus, the Wood River system likely receives substantial immigration from neighbouring watersheds, such as the Nushagak River system, which supports highly productive runs. Although no data on population productivity in the Wood River system exist, our results suggest source-sink dynamics for the two species, a finding relevant to other systems where salmonid population sizes are limited by habitat factors.