On the mechanism of drug-induced acceleration of phospholipid translocation in the human erythrocyte membrane

Small amphiphilic compounds (M(r)<200 Da) such as anaesthetics and hexane derivatives with different polar groups produced a concentration-dependent acceleration of the slow passive transbilayer movement of NBD-labelled phosphatidylcholine in the human erythrocyte membrane. Above a threshold concentration characteristic for each compound, the flip rate gradually increased at increasing concentrations in the medium. For compound concentrations required to produce a defined flip acceleration, corresponding membrane concentrations were estimated using reported octanol/water partition coefficients. The effective threshold membrane concentrations (50-150 mmol l(-1)) varied in the order: hexylamine>isoflurane=hexanoic acid>hexanol=chloroform>hexanethiol=1,1,2,2-tetrachloroethane>chlorohexane. Apolar hexane, which mainly distributes in the apolar membrane core, was much less effective and supersaturating concentrations were required to enhance flip. Localization of the drug at the lipid-water interface seems to be required for flip acceleration. Such a localization may increase the lateral pressure in this region and the bilayer curvature stress with concomitant decrease of order and rigidity at the interface. This unspecific bilayer perturbation is proposed to enhance the probability of formation of hydrophobic defects in the bilayer, facilitating penetration of the polar head group of the phospholipid into the apolar membrane core.     

The two biosynthetic routes leading to phosphatidylcholine in yeast produce different sets of molecular species. Evidence for lipid remodeling

Phosphatidylcholine (PC), a major lipid class in the membranes of eukaryotes, is synthesized either via the triple methylation of phosphatidylethanolamine (PE) or via the CDP-choline route. To investigate whether the two biosynthetic routes contribute differently to the steady-state profile of PC species, i.e., PC molecules with specific acyl chain compositions, the pools of newly synthesized PC species were monitored by labeling Saccharomyces cerevisiae with deuterated precursors of the two routes, (methyl-D3)-methionine and (D13)-choline, respectively. Electrospray ionization tandem mass spectrometry (ESI-MS/MS) revealed that the two PC biosynthetic pathways yield different sets of PC species, with the CDP-choline route contributing most to the molecular diversity. Moreover, yeast was shown to be capable of remodeling PC by acyl chain exchange at the sn-1 position of the glycerol backbone. Remodeling was found to be required to generate the steady-state species distribution of PC. This is the first study demonstrating a functional difference between the two biosynthetic routes in yeast.     

In vitro models to study compressive strain-induced muscle cell damage

Skeletal muscle tissue is highly susceptible to sustained compressive straining, eventually leading to tissue breakdown in the form of pressure sores. This breakdown begins at the cellular level and is believed to be triggered by sustained cell deformation. To study the relationship between compressive strain-induced muscle cell deformation and damage, and to investigate the role of cell-cell interactions, cell-matrix interactions and tissue geometry in this process, in vitro models of single cells, monolayers and 3D tissue analogs under compression are being developed. Compression is induced using specially designed loading devices, while cell deformation is visualised with confocal microscopy. Cell damage is assessed from viability tests, vital microscopy and histological or biochemical analyses. Preliminary results from a 3D cell seeded agarose model indicate that cell deformation is indeed an important trigger for cell damage; sustained compression of the model at 20% strain results in a significant increase in cell damage with time of compression, whereas damage in unstrained controls remains constant over time.     

Efficient production of Arthromyces ramosus peroxidase by Aspergillus awamori

The heterologous production of Arthromyces ramosus peroxidase (ARP) was analysed in the filamentous fungus Aspergillus awamori under control of the inducible endoxylanase promoter. Secretion of active ARP was achieved up to 800 mg l(-1) in shake flask cultures. Western blot analysis showed that an rARP product of the correct molecular weight was produced. In contrast to several other studies about heterologous production of heme containing peroxidases, our results suggest that in A. awamori no heme limitation exists during overproduction of ARP.     

The production of antibody fragments and antibody fusion proteins by yeasts and filamentous fungi

In this review we will focus on the current status and views concerning the production of antibody fragments and antibody fusion proteins by yeasts and filamentous fungi. We will focus on single-chain antibody fragment production (scFv and V_HH) by these lower eukaryotes and the possible applications of these proteins. Also the coupling of fragments to relevant enzymes or other components will be discussed. As an example of the fusion protein strategy, the 'magic bullet' approach for industrial applications, will be highlighted.     

Determination of nifedipine in human plasma by flow-injection tandem mass spectrometry

For use in clinical studies, a fast and sensitive assay method was developed for the determination of nifedipine in human plasma samples. The assay method is based on tandem mass spectrometry detection (HPLC–MS–MS). The effect of flow injection as well as HPLC separation on the results of the nifedipine determination were evaluated. The limit of quantification is 0.5 ng/ml and the accuracy (as determined by spiking recovery) was found to be good.     

Baroreflex sensitivity, blood pressure buffering, and resonance: what are the links? Computer simulation of healthy subjects and heart failure patients.

The arterial baroreflex buffers slow (<0.05 Hz) blood pressure (BP) fluctuations, mainly by controlling peripheral resistance. Baroreflex sensitivity (BRS), an important characteristic of baroreflex control, is often noninvasively assessed by relating heart rate (HR) fluctuations to BP fluctuations; more specifically, spectral BRS assessment techniques focus on the BP-to-HR transfer function around 0.1 Hz. Skepticism about the relevance of BRS to characterize baroreflex-mediated BP buffering is based on two considerations: 1) baroreflex-modulated peripheral vasomotor function is not necessarily related to baroreflex-HR transfer; and 2) although BP fluctuations around 0.1 Hz (Mayer waves) might be related to baroreflex BP buffering, they are merely a not-intended side effect of a closed-loop control system. To further investigate the relationship between BRS and baroreflex-mediated BP buffering, we set up a computer model of baroreflex BP control to simulate normal subjects and heart failure patients. Output variables for various randomly chosen combinations of feedback gains in the baroreflex arms were BP resonance, BP-buffering capacity, and BRS. Our results show that BP buffering and BP resonance are related expressions of baroreflex BP control and depend strongly on the sympathetic gain to the peripheral resistance. BRS is almost uniquely determined by the vagal baroreflex gain to the sinus node. In conclusion, BP buffering and BRS are unrelated unless coupled gains in all baroreflex limbs are assumed. Hence, the clinical benefit of a high BRS is most likely to be attributed to vagal effects on the heart instead of to effective BP buffering.     

Influence of gravity compensation on muscle activity during reach and retrieval in healthy elderly

IntroductionArm support like gravity compensation may improve arm movements during stroke rehabilitation. It is unknown how gravity compensation affects muscle activation patterns during reach and retrieval movements. Since muscle activity during reach is represented by a component varying with movement velocity and a component supposedly counteracting gravity, we hypothesized that gravity compensation decreases the amplitude of muscle activity, but does not affect the pattern. To examine this, we compared muscle activity during well defined movements with and without gravity compensation in healthy elderly.MethodsTen subjects performed reach and retrieval movements with and without gravity compensation. Muscle activity of biceps, triceps, anterior, middle and posterior parts of deltoid and upper trapezius was compared between the two conditions.ResultsThe level of muscle activity was lower with gravity compensation in all muscles, reaching significance in biceps, anterior deltoid and trapezius (p ? 0.026). The muscle activation pattern did not differ between movements with and without gravity compensation (p ? 0.662).DiscussionGravity compensation only influenced the level of muscle activity but not the muscle activation pattern in terms of timing. Future studies should examine if the influence of gravity compensation is comparable for stroke patients. This may stimulate early and intensive training during rehabilitation.