Importance of the G protein gamma subunit in activating G protein-coupled inward rectifier K(+) channels

Arachidonic acid (AA) is generated via Rac-mediated phospholipase A2 (PLA2) activation in response to growth factors and cytokines and is implicated in cell growth and gene expression. In this study, we show that AA activates the stress-activated protein kinase/c-Jun N-terminal kinase (SAPK/JNK) in a time- and dose-dependent manner. Indomethacin and nordihydroguaiaretic acid, potent inhibitors of cyclooxygenase and lipoxygenase, respectively, did not exert inhibitory effects on AA-induced SAPK/JNK activation, thereby indicating that AA itself could activate SAPK/JNK. As Rac mediates SAPK/JNK activation in response to a variety of stressful stimuli, we examined whether the activation of SAPK/JNK by AA is mediated by Rac1. We observed that AA-induced SAPK/JNK activation was significantly inhibited in Rat2-Rac1N17 dominant-negative mutant cells. Furthermore, treatment of AA induced membrane ruffling and production of hydrogen peroxide, which could be prevented by Rac1N17. These results suggest that AA acts as an upstream signal molecule of Rac, whose activation leads to SAPK/JNK activation, membrane ruffling and hydrogen peroxide production.     

Significance of kinetic degrees of freedom in operation of the actomyosin motor

The actomyosin motor as a principal functional component of cell motility is highly coordinated in regulating the participating molecular components. At the same time, it has to be flexible and plastic enough to accommodate itself to a wide variety of operational conditions. We prepared two different types of actomyosin systems. One is a natural intact actomyosin system with no artificial constraint on the kinetic degrees of freedom of the actin filaments, and the other is a regulated one with actin filaments supplemented by intra- and intermolecular crosslinking to suppress the kinetic degrees of freedom to a certain extent. Crosslinked actomyosin systems were found to remain almost insensitive to calcium regulation even when intact troponin-tropomyosin regulatory component was incorporated. Both the ATPase and the motile activities of the actin filaments sliding on myosin molecules were markedly lowered by the crosslinking. In contrast, once the crosslinking was cleaved, both properties returned to the normal as with intact actomyosin systems.     

Regeneration and maturation of daughter cell walls in the autospore-forming green alga<Emphasis Type="Italic"> Chlorella vulgaris</Emphasis> (Chlorophyta,Trebouxiophyceae)

Cell-wall synthesis in Chlorella vulgaris, an autospore-forming alga, was observed using the cell wall-specific fluorescent dye Fluostain I. The observation suggested two clearly distinguishable stages in cell-wall synthesis: moderate synthesis during the cell-growth process and rapid synthesis at the cell-division stage. We used electron microscopy to examine the structural changes that occurred with growth in the premature daughter cell wall during the cell-growth and cell-division phases. The cell began to synthesize a new daughter cell wall shortly after its release from the autosporangium. A very thin daughter cell wall, with a thickness of about 2 nm, was formed inside the mother cell wall and completely enveloped the outer surface of the plasma membrane of the cell. The daughter cell wall gradually increased in thickness from 2 to 3.8 nm. During the protoplast-division phase in the cell-division stage, the daughter cell wall expanded on the surface of the invaginating plasma membrane of the cleavage furrow, accompanied by active synthesis of the cell wall, which increased in thickness from 3.8 to 6.1 nm. The daughter cell matured into an autospore while completely enclosed by its own thickening (from 6.1 to 17 nm) wall. Finally, the released daughter cell was enclosed by its own cell wall after the mother cell wall burst. The daughter cell with mature wall thickness (17–21 nm) emerged as a small, but complete, autospore.     

Effects of a novel gaseous antioxidative system containing a rosemary extract on the oxidation induced by nitrogen dioxide and ultraviolet radiation

Rosemary is commonly used as a spice and a flavoring agent in food processing. Although the antioxidative properties of its extracts have been investigated, there have been few reports on the volatile components of rosemary. We designed a novel antioxidative system which can generate the volatile constituents in the gaseous phase from a rosemary extract and evaluated the gaseous antioxidative activities against both lipid peroxidation and cell death induced by nitrogen dioxide and ultraviolet radiation. The antioxidative effects of the major volatile components on the oxidation of linoleic acid induced by azo compounds were also investigated in a solution. The volatile components in the novel antioxidative system suppressed the Jurkat cell death induced by nitrogen dioxide and the intracellular formation of reactive oxygen species in fibroblast cells induced by ultraviolet radiation. 1,8-Cineole among the volatile components exerted an antioxidative effect against the oxidation of linoleic acid in a solution induced by azo compounds and ultraviolet radiation. These data suggest that the volatile constituents of a rosemary extract had antioxidative properties and that gaseous exposure antioxidant is a promising method for promoting health.     

Formation of N-(hexanoyl)ethanolamine, a novel phosphatidylethanolamine adduct, during the oxidation of erythrocyte membrane and low-density lipoprotein

The primary amino groups of biomolecules such as aminophospholipids, as well as proteins, are the potential targets of covalent modifications by lipid peroxidation products; however, little attention has been paid to the modification of aminophospholipids such as phosphatidylethanolamine (PE). The purpose of this study is to characterize the formation of a novel modified phospholipid, N-(hexanoyl)phosphatidylethanolamine (HEPE), in the reaction of PE with lipid hydroperoxides using mass spectrometric analyses. Upon reaction of egg PE with 13-hydroperoxyoctadecadienoic acid or other oxidized polyunsaturated fatty acids followed by phospholipase D-mediated hydrolysis, the formation of N-(hexanoyl)ethanolamine (HEEA), a head group of HEPE, was confirmed by isotope dilution liquid chromatography/tandem mass spectrometry. Moreover, increasing HEEA was detected in the hydrolysates of oxidized erythrocyte ghosts and low-density lipoprotein with their increasing lipid peroxidation levels. Collectively, these results suggest that the N-hexanoylated product of phospholipid, HEPE, can be generated during lipid peroxidation and may serve as one mechanism for the covalent modification of aminophospholipids in vivo.     

Plasma adrenomedullin concentration is increased in patients with peripheral arterial occlusive disease associated with vascular inflammation

Adrenomedullin (AM), a potent vasodepressor, is known to have anti-atherosclerotic and anti-inflammatory effects. However, there is no information about its level in severe atherosclerotic diseases, such as peripheral arterial occlusive disease (PAOD). The present study investigated the plasma concentration of AM and several inflammatory parameters in 72 patients with and without PAOD. The plasma AM concentration in patients with PAOD was significantly higher than in those without PAOD. Its concentration had significant correlations with ankle-brachial index and Fontaine's stage. The plasma AM level also correlated with high sensitive C-reactive protein and interleukin-6. As an additional study, plasma levels of two forms of AM drawn from the femoral artery and saphenous vein were measured in 27 other subjects. Both mature and intermediate forms of plasma AM in the femoral artery and saphenous vein were higher in patients with PAOD than in those without PAOD. A significant step-up of the mature form of AM from the femoral artery to the saphenous vein was observed. Our findings indicate that the plasma AM concentration was elevated in patients with PAOD in proportion to the severity of the disease and associated with vascular inflammation. An increased production of AM in PAOD may play a protective role against advanced atherosclerosis with an inflammatory signature.     

Adrenomedullin as a sensitive marker for coronary and peripheral arterial complications in patients with atherosclerotic risks

Plasma adrenomedullin (AM) levels are elevated in various pathological states including cardiovascular and inflammatory diseases. The present study investigated whether an increased AM level is a marker of vascular complications in patients with atherosclerotic risks. In 114 patients with cardiovascular risks and/or diseases including ischemic heart disease (IHD) and peripheral arterial disease (PAD), plasma AM concentration and other inflammatory markers such as high sensitive C-reactive protein (CRP) and interleukin (IL)-6 were examined. The plasma AM level was not altered by the absence or presence of each of four major risk factors, i.e., hypertension, diabetes mellitus, hyperlipidemia, and smoking and its level was not significantly correlated with blood pressure, plasma glucose, or serum lipid levels. The patients with IHD had a significantly higher concentration of plasma AM than those without IHD. The AM level in subjects with PAD was also increased significantly compared with those without PAD. The plasma AM was strongly correlated with inflammatory parameters such as CRP and IL-6. Among AM, CRP, and IL-6, however, only AM was an independent predictor for both IHD and PAD by multiple logistic regression analysis. Our findings suggest the possibility that plasma AM is a novel sensitive marker for the presence of vascular lesions in patients with atherosclerotic risks.     

Load-dependent regulation of neuromuscular system

Roles of gravitational loading, sarcomere length, and/or tension development on the electromyogram (EMG) of soleus and afferent neurogram recorded at the L5 segmental level of spinal cord were investigated during parabolic flight of a jet airplane or hindlimb suspension in conscious rats. Both EMG and neurogram levels were increased when the gravity levels were elevated from 1-G to 2-G during the parabolic flight. They were decreased when the hindlimbs were unloaded by exposure to actual microgravity or by suspension. These phenomena were related to passive shortening of muscle fibers and/or sarcomeres. Unloading-related decrease in sarcomere length was greater at the central rather than the proximal and distal regions of fibers. These activities and tension development were not detected when the mean sarcomere length was less than 2.03 micrometers. It is suggested that load-dependent regulation of neuromuscular system is related to the tension development which is influenced by sarcomere length.