Effects of seabird vectors on the fate, partitioning, and signatures of contaminants in a High Arctic ecosystem

Seabirds bioaccumulate contaminants from prey, transport them to their nesting sites, and deposit them in their excreta and carcasses, thereby focusing marine-derived contaminants into remote, terrestrial receptor sites. In the case of organochlorine chemicals transported by northern fulmars (Fulmarus glacialis) to a High Arctic seabird colony on Devon Island, Nunavut, Canada (76°13'N, 89°14'W), this contaminant pathway dominates all others. In freshwater ponds below the nesting cliffs, concentrations of organochlorine contaminants characteristic of fulmar input were 2- to 45-fold higher in sediments and water (depending on seabird input to the particular pond) than in ponds remote from the colony. Air-water fugacity quotients for the ponds decreased with seabird input, indicating that fulmar contaminant input shifts air-water partitioning to increasingly favor volatilization to air. Although contaminant evasion from water was favored, direct evidence of it was not detected in air samples. For PCBs, congener profiles of pond sediments or water became more similar to seabird sources as seabird input increased, and less similar to air profiles. Based on measurements of contaminants in fulmars and other local environmental media, this study presents the first application of fugacities and multivariate source apportionment statistics to resolve seabird biological vectors.     

Ultraviolet stimulated electron source for use with low energy plasma instrument calibration

We have developed and demonstrated a versatile, compact electron source that can produce a mono-energetic electron beam up to 50 mm in diameter from 0.1 to 30 keV with an energy spread of <10 eV. By illuminating a metal cathode plate with a single near ultraviolet light emitting diode, a spatially uniform electron beam with 15% variation over 1 cm(2) can be generated. A uniform electric field in front of the cathode surface accelerates the electrons into a beam with an angular divergence of <1° at 1 keV. The beam intensity can be controlled from 10 to 10(9) electrons cm(-2) s(-1).     

Detection of donor-specific hyporesponsiveness following late failure of human renal allografts

Limiting dilution assays to measure the frequency of interleukin-2-secreting peripheral blood T cells were carried out in patients, whose renal allografts had failed due to acute rejection (9 patients) and in patients whose grafts failed more than two years after transplantation without any recent evidence of acute rejection. Using a modified form of the assay we demonstrate that nearly half of 18 patients whose renal transplants had failed after more than two years have low or undetectable HTLp frequencies against donor, but not third-party DR antigens. No such difference was observed in any of the nine patients studied whose transplants were lost from early acute rejection. These results provide the first indication that, as in rodent models of transplantation, T cell unresponsiveness towards donor MHC antigens can occur following prolonged residence of an allograft in humans. Furthermore, the results suggest that chronic rejection may be driven by mechanisms other than direct allorecognition. The assay may be a valuable tool to study the evolution of donor-specific direct T cell alloresponsiveness in patients with well-functioning grafts.     

Medical-resource use for suspected tuberculosis in a New York City hospital

OBJECTIVE: To compare resource use by diagnostic outcome among hospital admissions during which tuberculosis (TB) was suspected. DESIGN: Retrospective study based on chart review and microbiology laboratory data. SETTING: The department of medicine in a municipal hospital serving central Brooklyn, New York. PARTICIPANTS: We identified all adult admissions in 1993 during which TB was suspected. We assigned each admission to one of four mutually exclusive groups defined by the results of microbiological tests (acid-fast bacilli [AFB] smear and culture): culture-positive and smear-positive (C+S+); culture-positive and smear-negative (C+S-); culture-negative and smear-positive (C-S+); or culture-negative and smear-negative (C-S-). Each admission was divided into two separate periods to which the utilization of medical resources was assigned: the diagnostic and the postdiagnostic periods, which were separated by the date of receipt of the first definitive culture report. RESULTS: Data on 519 admissions (93 C+S+; 57 C+S-; 30 C-S+; and 339 C-S-) were analyzed. Although C+S+ were more likely than other groups to have an admitting diagnosis of TB, approximately one quarter of the admissions without TB (C-S+, C-S-) were admitted with the principal diagnosis of TB. For the four groups, C+S+, C+S-, C-S+, and C-S-, the respective rates of TB isolation and anti-TB treatment, and median lengths of isolation were 98%, 87%, and 34 days; 74%, 74%, and 7 days; 83%, 83%, and 15 days; and 44%, 29%, and 0 days. During the diagnostic period, the rate and length of isolation were similar in the AFB-smear-positive groups (C+S+ and C-S+). We estimated that admissions without culture-proven TB (C-S+ and C-S-) accounted for 3,174 (36%) of the 8,712 days of TB isolation expended and for 65% of the 16,671 days of anti-TB treatment. The vast majority of this resource consumption (2,737 [86%] of 3,174 days of isolation) occurred during the diagnostic period before a definitive culture result was known. CONCLUSIONS: Our results suggest that prolonged diagnostic uncertainty and misclassification of cases due to false-positive and false-negative smears are associated with substantial medical-resource consumption. New diagnostic modalities that reduce the period of diagnostic uncertainty could reduce the utilization of resources later found to be unnecessary.     

Dynamics of clot growth induced by thrombin diffusing into nonstirred citrate human plasma

We have tested whether action potential-evoked Ca2+ influx is required to initiate clathrin-mediated synaptic vesicle endocytosis in the lamprey reticulospinal synapse. Exo- and endocytosis were temporally separated by a procedure involving tonic action potential stimulation and subsequent removal of extracellular Ca2+ (Ca2+e). A low concentration of Ca2+ ([Ca2+]e of 11 microM) was found to be required for the induction of early stages of endocytosis. However, the entire endocytic process, from the formation of clathrin-coated membrane invaginations to the generation of synaptic vesicles, proceeded in the absence of action potential-mediated Ca2+ entry. Our results indicate that the membrane of synaptic vesicles newly incorporated in the plasma membrane is a sufficient trigger of clathrin-mediated synaptic vesicle endocytosis.