The use of cobalt ions as a collisional quencher to probe surface charge and stability of fluorescently labeled bilayer vesicles

Co2+ quenched the fluorescence of the lipid probes NBD-phosphatidylethanolamine (NBD-PE) and lissamine-rhodamine phosphatidylethanolamine (N-Rh-PE) incorporated into lipid vesicles, according to a collisional quenching mechanism in agreement with the Stern-Vollmer law. The quenching coefficient (Q) for NBD-PE, incorporated into uncharged phosphatidylcholine (PC) vesicles was 13.8 M-1. This value was equal to the quenching coefficient of water-soluble NBD-taurine in aqueous solution, indicating that Co2+ was readily accessible to the outer surface of PC vesicles. In phosphatidylserine-phosphatidylethanolamine (PS-PE) (1:1) vesicles, quenching was also proportional to Co2+ concentration but Q was 114 mM-1, some 8000-fold smaller. Using the Gouy-Chapman-Stern model we demonstrated that the surface density of Co2+ bound to lipid was linear with Co2+ concentration in the medium up to 7%. Co2+-associated phospholipid would in turn quench NBD-PE or N-Rh-PE by collisional quenching with lateral diffusion. We investigated the ability of Co2+ to permeate PS-PE (1:1) vesicles. Co2+ quenched fluorophores on the outer surface of large unilamellar vesicles, formed by reverse-phase evaporation. In small unilamellar vesicles Co2+ quenched probes on both outer and inner surfaces, indicating rapid permeation of the ions into the vesicles. Using stopped-flow rapid mixing, we measured the rate of influx of Co2+, and correcting for surface potential using the Gouy-Chapman-Stern model, we calculated a permeability coefficient of 10(-12) cm/s for Co2+ concentrations below 300 microM. Above this concentration, there was a very steep rise in the permeability coefficient, indicating that binding of Co2+ induces defects in the bilayer of these vesicles. This may be related to the ability of the vesicles to undergo membrane fusion. A method for calculating the membrane surface potential from Co2+ quenching data is presented.     

Changing patterns of cerium reactivity in developing ovarian oocytes of the hamster

In developing ovarian oocytes of 2-day-old, 12-day-old and adult hamsters, oxidative enzyme activity as demonstrated by the cerium technique is strongest at 12 days and occurs principally in those oocytes which have begun rapid growth. The reaction is associated with the outer mitochondrial membrane, nearby cytoplasm, endoplasmic reticulum and nuclear envelope. Once antrum formation has begun and the mitochondria have reached the dormant (storage) stage, cerium reactivity ceases. In adults, reaction occurs at the same stages of oocyte development but is weaker and limited to the mitochondria and their immediate vicinity.     

Rationalization of some genetic anticodonic assignments

The genetic code appears to be a logic matrix in which, generally speaking, there is a correlation between the hydrophobicities of amino acids and their anticodonic nucleotides. There are several exceptions to this generality, however, and using previous data on hydrophobicity and binding constants, coupled with new data on reaction rates, we rationalize several of the anticodonic assignments.     

Age and growth of a colonizing minnow,Barbus anoplus,in a man-made lake in South Africa

Synopsis Aspects of the life history of Barbus anoplus were studied in Lake le Roux, a turbid man-made lake on the Orange River, South Africa. This minnow underwent a population explosion and successfully colonized the shoreline of the newly-formed lake during the early phases of reservoir filling. Male and female B. anoplus reach sexual maturity in one year at about 40 mm fork length. They have a multiple spawning habit with the first spawning in November–January and the second in February–March. The growth of the two resulting cohorts is discussed. It is proposed that the offspring from the second spawning not only acts as a ‘back-up’ but is capable of prolonging the life of that year-class into an additional reproductive season. Most of the minnows die after their second summer, but more offspring from the second spawning, especially females, live into a third summer. Females attain a larger maximum size (73 mm FL) and age (3–4 years) than males (60 mm FL, 2–3 years). B. anoplus is small and short-lived with a high seasonal reproductive potential, which is in contrast to the larger Barbus species in the Orange River system. These life-history traits enable the species to colonize and successfully inhabit unstable environments and probably account for its widespread distribution.     

Reduction in headache patients' medical expenses associated with biofeedback and relaxation treatments

Comparisons are made of self-reported medical costs from a sample of headache patients who underwent various combinations of relaxation training and biofeedback training. The average costs for the 2 years prior to self-regulatory treatment were $955±480 (3 SEM) for 45 patients; for the 2 years after completing treatment the average costs were $52±28 (3 SEM) for patients. Within the limitations of the study, medical costs do seem to have been markedly reduced.This research was supported by a grant from NINCDS, NS-15235.     

DNA single-strand breaks,double-strand breaks,and crosslinks in rat testicular germ cells: Measurements of their formation and repair by alkaline and neutral filter elution

This work describes a neutral and alkaline elution method for measuring DNA single-strand breaks (SSBs), DNA double-strand breaks (DSBs), and DNA-DNA crosslinks in rat testicular germ cells after treatments in vivo or in vitro with both chemical mutagens and gamma-irradiation. The methods depend upon the isolation of testicular germ cells by collagenase and trypsin digestion, followed by filtration and centrifugation. ¹³⁷Cs irradiation induced both DNA SSBs and DSBs in germ cells held on ice in vitro. Irradiation of the whole animal indicated that both types of DNA breaks are induced in vivo and can be repaired. A number of germ cell mutagens induced either DNA SSBs, DSBs, or cross-links after in vivo and in vitro dosing. These chemicals included methyl methane sulfonate, ethyl methane sulfonate, ethyl nitrosurea, dibromochlorpropane, ethylene dibromide, triethylene melamine, and mitomycin C. These results suggest that the blood-testes barrier is relatively ineffective for these mutagens, which may explain in part their in vivo mutagenic potency.This assay should be a useful screen for detecting chemical attack upon male germ-cell DNA and thus, it should help in the assessment of the mutagenic risk of chemicals. In addition, this approach can be used to study the processes of SSB, DSB, and crosslink repair in DNA of male germ cells, either from all stages or specific stages of development.Abbreviations DBCP dibromochlorpropane - DSB(s) DNA double-strand break(s) - EDB ethylene dibromide - EMS ethyl methane sulfonate - ENU ethyl nitrosurea - MC mitomycin C - MMS methyl methane sulfonate - SDS sodium dodecyl sulfate - SSB (s) DNA single-strand break(s) - TEM triethylene melamine - UDS unscheduled DNA synthesis     

Management of localized non-Hodgkin's lymphoma

Non-Hodgkin''s lymphomas (NHLs) are a heterogeneous group of disorders that vary widely in response to therapy. In Canada the modified Rappaport classification is used to categorize NHL. To facilitate the reporting and comparison of treatment results all cases should also be categorized in the terminology of the National Cancer Institute''s working formulation. The choice of therapy should be guided by specific prognostic factors: stage and bulk of the disease, patient''s age, presence of systemic symptoms and histologic subtype. Of these, the last appears to be the most important. Radiotherapy (RT) is the treatment of choice in localized low-grade lymphomas with favourable prognoses, while bimodal therapy (RT and chemotherapy [CT]) is warranted in presentations with unfavourable prognoses. Regional irradiation alone is indicated in intermediate-grade lymphomas with good prognoses (i.e., pathological stage I or II or clinical stage IA or IIA localized disease of small bulk in young patients). All other patients require CT followed by RT. The results of CT alone are encouraging but remain experimental. Aggressive therapy with multidrug regimens that include central nervous system prophylaxis is the foundation for successful treatment of high-grade NHL such as lymphoblastic lymphoma and diffuse small-noncleaved-cell lymphomas. Low-dose RT should be given to sites of bulky disease.     

Geographical and temporal variation in the calls of the Manx shearwater Puffinus puffinus and British storm petrel Hydrobates pelagicus

The geographical variation in the calls of the Manx shearwater Puffinus puffinus and British storm petrel Hydrobales pelagicus was investigated, as well as its temporal stability in the shearwater. Within-island call variation was not apparent in Puffinus , although male calls were relatively more distinct locally than female calls. This is discussed in relation to the differential dispersal of the sexes. Between-island call variation was apparent in both Puffinus and Hydrobates , but the variation was continuous, and not discrete. Call divergence is unrelated to inter-island distance, and may reflect the influence of coastlines on each species'dispersal opportunities. The calls of a shearwater population changed over a period of six to seven years, apparently due to the appearance of new birds rather than surviving birds altering their calls. Male calls changed more than female calls, which, taken with dispersal factors, suggests that calls are transmitted across generations at least in part by cultural copying. The vocal'drift'over time therefore probably results from errors in this copying process.