Study on excitation phenomena in model systems are interesting as a counter part of investigations on living tissue. The occurrence of excitation in various kinds of synthetic membrane systems has been reported since the last 40 years. Recently we found that a polypeptide membrane spontaneously generated electrical pulses under a concentration gradient of salt in the absence of any other external forces.In this article, we describe the excitable membrane accompanying a conformational change prepared from synthetic polypeptide, and discuss the relation between the excitation phenomena and the conformational transition and also membrane structure.

View full abstract

Membrane fusion plays a crucial role in intracellular vesicular transport, intercellular fusion and viral infectivity. The fusion reaction has been supposed to underlie the following three steps ; (i) specific docking of two membranes, (ii) perturbation of lipid bilayer at fusion point (s) and formingfusion pore (s), (iii) dilation of fusion pore (s). For the intracellular membrane fusion in membrane trafficking pathways, the recent convergence of genetic and biochemical approaches has led to the identification of a number of proteins that involved in specific docking of two membranes (step (i)). However, the details in step (ii) have not been clarified. In this review, I will focus on putative “fusion peptide” of viral fusogenic proteins as an activator of the step (ii). Through the works on the fusion of liposomes mediated by several synthetic peptides that are derived from the fusion peptide of influenza virus hemagglutinin, we found that the fusion is triggered when the peptides become more hydrophobic under fusion-competent conditions, and also found that the common structural features of the fusogenic peptides is not “amphiphilic helical structure”. The amphiphilic peptides appearto require other factor (s) to cause fusion. I propose that uneven distribution of the side-chain bulkiness of peptide in ordered structure is important factor for fusion active peptide.

View full abstract

[in Japanese]

View full abstract

Microporous polypropylene membranes were prepared via thermally-induced phase separation from mixtures of polypropylene/soybean oil, polypropylene/oleic acid, and polypropylene/linoleic acid. The phase diagram of each system was obtained by thermal analysis and cloud point measurements. It was proved that each system has a liquid-liquid phase separation region at concentrations less than the monotectic composition. A cellular structure was obtained for each system, which is the typical structure for liquid-liquid phase separation via slow cooling. Fine structure with tiny polypropylene spherulites was obtained via quenching process. Mobility of diluent was related with its rejection during the polypropylene spherulite formation. A melt spinning apparatus was designed to produce microporous hollow fiber membranes. The mechanical strength of the hollow fiber seemed to be related to solution viscosity. Polypropylene/soybean oil samples had much greater solution viscosity than the other systems, and formed fibril structures with enhanced mechanical strength.

View full abstract

The epithelial cell sheet in the gastrointestinal mucosa is a permselective sophisticated membrane, which serves as a potent permeation barrier to water-soluble and large molecular weight xenobiotics. Fatty acids such as oleic acid and capric acid efficiently enhance the intestinal absorption of poorly absorbed drugs due to the transient reduction of the barrier resistance. However, the mechanisms have not been completely elucidated and their effective and safe use should be desired in drug delivery. It was proposed that these fatty acids could enhance the permeation of drugs by perturbing the lipid bilayer of brush-border membrane. However, it seems unlikely to explain that they increase the mucosal permeation of macromolecular compounds which cannot pass through cell membranes. We have found that the permeability enhancement by the fatty acids is temperature-dependent with being maximal at 37°C, and that it is inhibited by the membrane-permeable SH-modifiers, corresponding with the reduction in sulfhydryl content in the brush-border membrane, and high concentration of potassium ion in the lumen. The sulfhydryl modification of brush-border membrane inhibited the oleic acid-induced increase in membrane fluidity in the SH-protein fraction but not in the lipid bilayer. In addition, W-7, a specific calmodulin inhibitor, significantly inhibited the oleic acid-induced increase in membrane permeability, suggesting the possible roles of calmodulin-dependent protein kinases in the mechanism underlying the permeability enhancement of the intestinal mucosa.
The results discussed in this study suggest that a signal from the action of oleic acid on the brushborder membrane is transmitted via some subcellular molecular systems to the cell skeleton to increase the mucosal drug permeability. However, further detail studies are needed to estabilish this mechanism.

View full abstract

A new polyimide hollow fiber membrane for air separation was develpoed. It has a high O₂permeation rate and a high O₂/N₂ selectivity.
The modules made of the new hollow fibers have high productivities and high recovery of 99% N₂. They shows excellent N₂ enrichment performances.

View full abstract