Procedure using voltage-sensitive spin-labels to monitor dipole potential changes in phospholipid vesicles: The estimation of phloretin-induced conductance changes in vesicles

Summary Voltage-sensitive membrane potential probes were used to monitor currents resulting from positive or negative charge movement across small and large unilamellar phosphatidylcholine (PC) vesicles. Positive currents were measured for the paramagnetic phosphonium ion or for K⁺-valinomycin. Negative currents were indirectly measured for the anionic proton carriers CCCP and DNP by monitoring transmembrane proton currents. Phloretin, a compound that is believed to decrease dipole fields in planar bilayers, increases positive currents and decreases negative currents when added to egg PC vesicles. In these vesicles, positive currents are increased by phloretin addition to a much larger degree than CCCP currents are reduced. This asymmetry, with respect to the sign of the charge carrier, is apparently not the result of changes in the membrane dielectric constant. It is most easily explained by deeper binding minima at the membrane-solution interface for the CCCP anion, when compared to the phosphonium. The measured asymmetry and the magnitudes of the current changes are consistent with the predictions of a point dipole model. The use of potential-sensitive probes to estimate positive and negative currents, provides a methodology to monitor changes in the membrane dipole potential in vesicle systems.     

Immediate and delayed effects of poor developmental conditions on growth and flight ability of juvenile mourning doves Zenaida macroura

Adaptations that minimize the effects of stress are important components of avian development and have a role in structuring the relationship between development and fitness. I examined the effect of experimental manipulations of developmental stress during the nestling and fledgling stages on weight gain, growth in structural size, and take‐off flight speed of juvenile mourning doves Zenaida macroura. Brood size was manipulated during the nestling stage (≤11 days) and feeding rates during the fledgling stage (13–25 days) using a full factorial design. Effects of nutritional stress differed between the two treatments and depended on the response that was measured and the age at which it was measured. Treatment effects on flight ability were delayed and were greater for the treatment during the nestling stage than during the fledgling stage. Immediate treatment effects were greater than delayed effects on weight and size. Young were able to minimize effects of stress on flight ability at early ages when they would be most vulnerable to predation. However, by 90 days birds from enlarged broods were slower and flight time at 90 days was negatively correlated with weight and size at 25 days. There was no evidence for a cost of compensatory growth after experimental treatments ended on flight ability at 90 days. Results suggest that the effects of stress occur in a hierarchical manner across phenotypic components and that at early ages flight ability is prioritized through phenotypic plasticity.     

Identification and Distribution of Phenylacetic Acid in the Brain of the Rat

Abstract: Phenylacetic acid, the major metabolite of phenylethylamine, has been identified and quantitated in rat brain regions by capillary column high-resolution gas chromatography mass spectrometry. Its distribution is heterogeneous and correlates with that of phenylethylamine. The values obtained were (ng/g ± SEM): whole brain, 31.2 ± 2.7; caudate nucleus, 64.6 ± 6.5; hypothalamus, 60.1 ± 7.4; cerebellum, 31.3 ± 2.9; brainstem, 33.1 ± 3.3, and the "rest," 27.6 ± 3.0.     

Analysis of folate cofactor levels in tissues using high-performance liquid chromatography

A method for the isolation and concentration of the monoglutamate forms of folate cofactors from tissues and for their subsequent separation and quantitation using HPLC coupled with uv detection at 284 nm is described. A chromatographic procedure utilizing Dowex 50 has been developed for the separation of the folate monoglutamates from a large portion of the nonfolate-related material following digestion of the polyglutamated froms with a highly purified preparation of rat liver conjugase. This chromatographic procedure combined with concentration of the Dowex eluate by lyophilization eliminates uv-absorbing material, which interferes with the detection and quantitation of the folate cofactors and makes possible uv measurement of the individual folates. Reverse-phase paired-ion chromatography on μBondapak C₁₈ coupled with uv detection allows direct quantitation of the folates in the nanogram range.     

Presence of a small plasmid in clinical isolates of Streptococcus pneumoniae

Twenty-four of 63 enteric Gram-negative organisms (38.1%) which were isolated from 35 apparently healthy Nigerian students were found to have low trimethoprim resistance (MIC less than 1000 mg/l). These isolates were also found to be resistant to several other antibiotics and trimethoprim resistance was found to be transferable from 15 (62.5%) of the trimethoprim resistant organisms into E. coli EC 1005. It is likely that the high percentage of trimethoprim resistance encountered in this study is related to the high rate of resistance transfer which was observed.     

Effects of amino acids and derivatives of cyclic adenosine 3′, 5′-monophosphate on the production of three exoenzymes by Staphylococcus, simulans biovar staphylolyticus

The extracellular protease, endopeptidase, and hexosaminidase produced by $\text{Staphylococcus}\text{,}\text{simulans}\text{biovar}\text{staphylolyticus}$ were neither induced nor repressed by amino acids but required a tryptic digest of casein for their production. Catabolite repression of exoenzyme production by glucose was not affected by exogenous cyclic adenosine 3′, 5′-monophosphate but was partially relieved by di- or monobutyryl derivatives of this compound.