Comparative 2H- and 31P-NMR study on the properties of palmitoyllysophosphatidylcholine in bilayers with gramicidin, cholesterol and dipalmitoylphosphatidylcholine

The stoichiometric palmitoyllysophosphatidylcholine (lysoPC)/gramicidin (4:1, mol/mol) lamellar complex (Killian, J.A., De Kruijff, B., Van Echteld, C.J.A., Verkleij, A.J., Leunissen-Bijvelt, J. and De Gier, J. (1983) Biochim. Biophys. Acta 728, 141-144) is a useful model system to investigate the various aspects of lipid protein interactions. To study the effect of gramicidin on local order and motion of 1-palmitoyl-sn-glycero-3-phosphocholine (lysoPC) we employed 31P and 2H nuclear magnetic resonance (NMR) using selectively deuterated lysoPC's and we compared the results to those obtained for lysoPC in bilayers with cholesterol (1:1, mol/mol) and dipalmitoylphosphatidylcholine (DPPC) (1:4, mol/mol). 2H-NMR experiments on acyl chain deuterated lysoPC showed similar quadrupole splittings in the liquid crystalline state for the lysoPC/DPPC and the lysoPC/gramicidin samples. In the lysoPC/cholesterol sample an increase of the quadrupole splitting was found. T1 measurements showed that gramicidin decreases the lysoPC acyl chain motion, especially at the C12 position. In the lysoPC/cholesterol sample an increase of motion was observed as compared to lysoPC in fluid bilayers of DPPC. 31P-NMR and 2-H-NMR measurements of lysoPC, deuterated at the alpha- and beta-position of the choline moiety, indicated an increase in headgroup flexibility in all samples as compared to the parent compound DPPC. In addition, a change in headgroup conformation was observed. The alpha- and beta-segments in all samples exhibited concerted motion. It was found that also in the polar headgroup gramicidin induces a decrease of the rate of motion.     

Sex Differences in the Steepness of Dominance Hierarchies in Captive Bonobo Groups

Bonobos have a reputation as a female-dominated and egalitarian species. We examined the 2 aspects of dominance in 6 captive bonobo groups. Females do not consistently evoke submission from all males in all contexts. Though females occupy the highest-ranking positions in the dominance hierarchy, there are in each group males that obtain rather high ranks and are able to dominate ≥1 female. Thus female dominance is not complete and hierarchies can be better described as nonexclusive female dominance. We studied egalitarianism by measuring linearity and steepness of dominance hierarchies. The hierarchies of all groups are highly linear. Hierarchies among males are steeper than among females. On average, male bonobos are more despotic than females, but females too can have despotic relations, both with other females and with males. Hence one can call bonobos in captivity semidespotic rather than egalitarian.     

Interaction between the canine diaphragm and intercostal muscles in lung expansion.

Changes in intrathoracic pressure produced by the various inspiratory intercostals are essentially additive, but the interaction between these muscles and the diaphragm remains uncertain. In the present study, this interaction was assessed by measuring the changes in airway opening (DeltaPao) or transpulmonary pressure (DeltaPtp) in vagotomized, phrenicotomized dogs during spontaneous inspiration (isolated intercostal contraction), during isolated rectangular or ramp stimulation of the peripheral ends of the transected C(5) phrenic nerve roots (isolated diaphragm contraction), and during spontaneous inspiration with superimposed phrenic nerve stimulation (combined diaphragm-intercostal contraction). With the endotracheal tube occluded at functional residual capacity, DeltaPao during combined diaphragm-intercostal contraction was nearly equal to the sum of the DeltaPao produced by the two muscle groups contracting individually. However, when the endotracheal tube was kept open, DeltaPtp during combined contraction was 123% of the sum of the individual DeltaPtp (P < 0.001). The increase in lung volume during combined contraction was also 109% of the sum of the individual volume increases (P < 0.02). Abdominal pressure during combined contraction was invariably lower than during isolated diaphragm contraction. It is concluded, therefore, that the canine diaphragm and intercostal muscles act synergistically during lung expansion and that this synergism is primarily due to the fact that the intercostal muscles reduce shortening of the diaphragm. When the lung is maintained at functional residual capacity, however, the synergism is obscured because the greater stiffness of the rib cage during diaphragm contraction enhances the DeltaPao produced by the isolated diaphragm and reduces the DeltaPao produced by the intercostal muscles.     

Antibiotic activity of isoxazolylnaphthoquinone imines on mice infected with Staphylococcus aureus

I. ALBESA, P. BOGDANOV, A. ERASO, N.R. SPERANDEO AND M.M. DE BERTORELLO. 1995. The antibiotic activity of new synthetic isoxazolylnaphthoquinone imines was studied. Pseudomonas aeruginosa ATCC 27853 and Escherichia coli ATCC 25922 were resistant to the four compounds studied (MIC > 128 µg ml⁻¹), but Staphylococcus aureus ATCC 25923, ATCC 29213 and 30 clinical isolates of Staph. aureus were inhibited by 2-hydroxy- N -(3,4-dimethyl-5-isoxazolyl)-1,4-naphthoquinone-4-imine (I). This compound diminished bloodstream infection of mice injected i.m. with Staph. aureus; septicaemia decayed significantly when I was applied at the beginning of the infection while when I was given 3 d after bacterial challenge, a significant protection was afforded. Bactericidal activity in serum increased during the 5 h after I was administered i.p.
The acetyl derivative of I had a high MIC but when inoculated orally in mice decreased the Staph. aureus counts in circulation. This protection occurred only when the schedule of administration started close to the bacterial challenge. Antibiotic activity in vivo may be associated with in vitro effects.     

Slow heat rate increases yeast thermotolerance by maintaining plasma membrane integrity.

Thermal resistance of Saccharomyces cerevisiae was found to be drastically dependent on the kinetics of heat perturbation. Yeasts were found to be more resistant to a plateau of 1 h at 50 degrees C after a slope of temperature increase (slow and linear temperature increments) than after a shock (sudden temperature change). Thermotolerance was mainly acquired between 40-50 degrees C during a heat slope, i.e., above the maximal temperature of growth. The death of the yeasts subjected to a heat shock might be related to the loss of membrane integrity: intracellular contents extrusion, i.e., membrane permeabilization, was found to precede cell death. However, the permeabilization did not precede cell death during a heat slope and, therefore, membrane permeabilization was a consequence rather than a cause of cell death. During a slow temperature increase, yeasts which remain viable may have time to adapt their plasma membrane and thus maintain membrane integrity.