Coupled Diffusion of Peripherally Bound Peptides along the Outer and Inner Membrane Leaflets

Transmembrane signaling implies that peripheral protein binding to one leaflet be detected by the opposite leaflet. Therefore, protein recruitment into preexisting cholesterol and sphingolipid rich platforms may be required. However, no clear molecular picture has evolved about how these rafts in both leaflets are connected. By using planar lipid bilayers, we show that the peripheral binding of a charged molecule (poly-lysine, PLL) is detected at the other side of the bilayer without involvement of raft lipids. The diffusion coefficient, D_P, of PLL differed by a factor of √2 when PLL absorbed to one or to both leaflets of planar membranes. Fluorescence correlation spectroscopy showed that the changes of the lipid diffusion coefficient, D_M, were even more pronounced. Although D_M remained larger than D_P on PLL binding to the first membrane leaflet, D_M dropped to D_P on PLL binding to both leaflets, which indicated that the lipids sandwiched between two PLL molecules had formed a nanodomain. Due to its small area of ∼20 nm² membrane electrostriction or leaflet interaction at bilayer midplane can only make a small contribution to interleaflet coupling. The tendency of the system to maximize the area where the membrane is free to undulate seems to be more important. As a spot with increased bending stiffness, the PLL bound patch in one leaflet attracts a stiffening additive on the other leaflet. That is to say, instead of suppressing undulations in two spots, two opposing PLL molecules migrate along a membrane at matching positions and suppress these undulations in a single spot. The gain in undulation energy is larger than the energy required for the alignment of two small PLL domains in opposite leafs and their coordinated diffusion. We propose that this type of mechanical interaction between two membrane separated ligands generally contributes to transmembrane signaling.     

Scale sensitivity of synthetic long‐term vegetation time series derived through overlay of short‐term field records

Questions: Is change in cover of dominant species driving the velocity of succession or is it species turnover (1)? Is the length of the time‐step chosen in sampling affecting our recognition of the long‐term rate of change (2)1 Location: 74 permanent plots located in the Swiss National Park, SE Switzerland, ca. 1900 m a.s.l. Methods: We superimpose several time‐series from permanent plots to one single series solely based on compositional dissimilarity. As shown earlier (Wildi & Schütz 2000) this results in a synthetic series covering about 400 to 650 yr length. Continuous power transformation of cover‐percentage scores is used to test if the dominance or the presence‐absence of species is governing secondary succession from pasture to forest. The effect of time step length is tested by sub‐samples of the time series. Results: Altering the weight of presence‐absence versus dominance of species affects the emerging time frame, while altering time step length is uncritical. Where species turnover is fast, different performance scales yield similar results. When cover change in dominant species prevails, the solutions vary considerably. Ordinations reveal that the synthetic time series seek for shortest paths of the temporal pattern whereas in the real system longer lasting alternatives exist. Conclusions: Superimposing time series differs from the classical space‐for‐time substitution approach. It is a computation‐based method to investigate temporal patterns of hundreds of years fitting between direct monitoring (usually limited to decades) and the analysis of proxy‐data (for time spans of thousands of years and more).     

Role of the serotoninergic raphe-hippocampus system for the antinocifensive effect of morphine

As revealed in earlier studies, the antinocifensive effect of morphine is brought about, among other things, with involvement of serotoninergic transmission mechanisms. In this context the role of the serotoninergic raphe-hippocampus system has been studied in this paper. Topical microinjections of serotonin into the dorsal hippocampus increased morphine analgesia in a dose-dependent fashion, while application into the striatum had no effect. Morphine injections into the median raphe nucleus in relatively low doses exert an antinocifensive effect which is inhibitable by methysergide. Lysergic acid diethylamide administered into the median raphe nucleus also abolished the effect of morphine in a dose-dependent manner. The results in connection with literature data lend support to the presumed integrative function of the serotoninergic raphe-hippocampus system in the mechanism of antinocifensive action of morphine.     

Porphyrin in Vogelfedern

Ohne Zusammenfassung