Fluoride metabolism in Acacia georginae Gidyea

1. The metabolism of fluoride in seedlings and small plants of Acacia georginae has been studied with the idea of finding the conditions under which the plant makes fluoroacetate in the laboratory. 2. Individual seedlings vary in the extent to which they take up fluoride and convert it into a form other than inorganic which is here called `organic' fluoride, F(org.). The differences between the toxicity of A. georginae Gidyea trees may therefore be genetic in origin. 3. The uptake of fluoride from solutions 0·525–1·05mm (10–20p.p.m.) was not large. In 1–4 days it reached 8 p.p.m. in the aerial parts and 16 p.p.m. in the roots. Unlike the distribution of the halogen in grass, total fluoride was greater than inorganic fluoride. It was almost a rule that more `organic' fluoride was present in the roots than in the aerial parts. 4. With higher concentrations of fluoride 10·5–15·75mm (200–300p.p.m.) much larger amounts of fluoride were taken up, especially by the roots, and much more apparent organic fluoride was formed. 5. pH had a large influence upon the intake, this being lowest at an initial pH8·4 and highest at pH4·0. The pH outside this range was not investigated.     

Aminophylline enhances contractility of frog skeletal muscle: an effect dependent on extracellular calcium

The effects of aminophylline (10-500 microM) on isometric twitch and tetanic forces were studied in vitro on frog semitendinosus muscle. Two hypotheses were tested: 1) that micromolar concentrations of aminophylline enhanced contractility of isolated skeletal muscle and 2) that the potentiating effect of aminophylline was dependent on the presence of extracellular calcium ions. Muscles were removed, placed in aerated Ringer solution at 20 degrees C, attached to a force transducer, and stimulated directly. Muscles in normal Ringer and aminophylline Ringer were compared throughout the frequency-force relationship from twitches to maximum tetanic force. Aminophylline increased twitch force significantly at concentrations as low as 25 microM. Over a range of stimulation frequencies, but especially at 10 and 20 Hz, aminophylline increased tetanic force. The potentiating effect of aminophylline (100 microM) was reduced or eliminated in calcium-free Ringer containing 10 mM magnesium. We conclude that aminophylline, at therapeutic concentrations, enhances muscle contractility, and the enhancement is dependent on the presence of extracellular calcium. These findings support the concept that aminophylline is effective in improving respiration in humans with airway obstruction by enhancing diaphragmatic contractility.     

The Ba fragment of complement factor B inhibits human B lymphocyte proliferation

Normal human B lymphocyte function is finely regulated by both positive and negative signals at each stage of activation, proliferation, and differentiation. Activation signals include antigen and surface Ig cross-linking agents such as anti-mu or anti-delta. Signals inducing proliferation include IL-2, high m.w.-B cell growth factor (BCGF), and low m.w.-BCGF. IL-2 as well as IL-6 and other partially characterized B cell differentiation factors can induce terminal differentiation of proliferating B cells into Ig-secreting plasma cells. Various C components have been described to regulate B cell function including Bb that enhances proliferation, C5a that enhances Ig production, and C3a that inhibits Ig production. In our study, we examined the ability of the factor B cleavage fragment Ba to influence human B cell function. Ba did not affect the activation of resting B cells but inhibited the proliferation of activated B cells stimulated with either high m.w.-BCGF or low m.w.-BCGF. The inhibition occurred with doses of Ba as low as 1 microgram/ml (29 nM). Ba was found to bind to activated human B lymphocytes in a saturable manner with an apparent K of approximately 25 nM and an apparent Bmax of 56,000 sites/cell. A peptide made of the carboxy terminal 10 amino acids of Ba (GHGPGEQQKR), was also found to inhibit growth factor induced proliferation of activated B cells but at an ID50 of approximately 5 microM. Finally, Ba was found to inhibit the terminal differentiation of Staphylococcus aweus Cowan-activated B cells stimulated with B cell differentiation factors but not Ig secretion by the partially differentiated EBV-transformed cell line SKW.6. Thus, concentrations of Ba achievable in vivo at sites of active inflammation were found to act on human B lymphocytes by inhibiting their proliferation. This may act to limit the immune response to a specific antigenic challenge.     

Characterization of chloramphenicol resistance inLactobacillus plantarum caTC2

A strain ofLactobacillus plantarum caTC2R isolated from a meat source was resistant to chloramphenicol (30 g/ml). Resistance was mediated through an inducible chloramphenicol acetyltransferase. Plasmid analysis of this strain showed three plasmids, of which the 8.5-kb plasmid apparently encodes the gene for chloramphenicol resistance. This plasmid was lost at high frequency (25%) when theLactobacillus was subcultured at a higher than optimal temperature (40°C).     

Subject: foraging

Research Notes on Avian Biology 1994: Selected Contributions from the 21st International Ornithological CongressBehavior: Foraging

Subject: foraging