Electromyographic analysis of walking in water in healthy humans

This study was designed to describe and clarify muscle activities which occur while walking in water. Surface electromyography (EMG) was used to evaluate muscle activities in six healthy subjects (mean age, 23.3 +/- 1.4 years) while they walked on a treadmill in water (with or without a water current) immersed to the level of the xiphoid process, and while they walked on a treadmill on dry land. The trials in water utilized the Flowmill which has a treadmill at the base of a water flume. Integrated EMG analysis was conducted for the quantification of muscle activities. In order to calculate the %MVC, the measurement of maximal voluntary contraction (MVC) of each muscle was made before the gait analysis, thus facilitating a comparison of muscle activities while walking in water with those on dry land. The %MVCs obtained from each of the tested muscles while walking in water, both with and without a water current, were all found to be lower than those obtained while walking on dry land at a level of heart rate response similar to that used when walking on dry land. Furthermore, the %MVCs while walking in water with a water current tended to be greater when compared to those while walking in water without a water current. In conclusion, the present study demonstrated that muscle activities while walking in water were significantly decreased when compared to muscle activities while walking on dry land, that muscle activities while walking in water tended to be greater with a water current than without, and that the magnitude of the muscle activity in water was relatively small in healthy humans. This information is important to design water-based exercise programs that can be safely applied for rehabilitative and recreational purposes.     

Origin of the scaling rule for fundamental living organisms based on thermodynamics

The regular relationships between metabolic energy and body mass M of unicellular organisms, poikilotherms and homeotherms were well known as general equations. The metabolic energy rate and the life span are proportional to M(0.75) and to M(0.25), respectively. As a result, the product of the metabolic energy rate and the life time, namely, life metabolic energy, is proportional to the mass of the living organism. The origin of the scaling rules for environmental organizing systems is as follows: (1) the scaling rules for internal energy, activation energy and free energy as a function of temperature and mass of a mole of molecules. (2) The majority of species of the living organisms have the same molecules such as polysaccharides, lipids, proteins and nucleic acids in nearly same the ratio. (3) The internal energy of reactants in living organisms is equilibrium with the internal energy of water. Then, the integrated metabolic energy over the synthesizing time depends on internal energy of water and is proportional to mass M, despite the synthesizing time of the system depending on reaction rate. The proportional constant is obtained based on the thermodynamics for fundamental living organisms such as unicellular organisms and plants. Information on the environmental organizing system is also discussed.     

Neither lipophilicity nor membrane-perturbing potency of phenothiazine maleates correlate with the ability to inhibit P-glycoprotein transport activity

Although phenothiazines are known as multidrug resistance modifiers, the molecular mechanism of their activity remains unclear. Since phenothiazine molecules are amphiphilic, the interactions with membrane lipids may be related, at least partially, to their biological effects. Using the set of phenothiazine maleates differing in the type of phenothiazine ring substitution at position 2 and/or in the length of the alkyl bridge-connecting ring system and side chain group, we investigated if their ability to modulate the multidrug resistance of cancer cells correlated with model membrane perturbing potency. The influence exerted on lipid bilayers was determined by liposome/buffer partition coefficient measurements (using the absorption spectra second-derivative method), fluorescence spectroscopy and calorimetry. Biological effects were assessed by a flow cytometric functional test based on differential accumulation of fluorescent probe DiOC(2)(3) by parental and drug-resistant cells. We found that all phenothiazine maleates were incorporated into lipid bilayers and altered their biophysical properties. With only few exceptions, the extent of membrane perturbation induced by phenothiazine maleates correlated with their lipophilicity. Within the group of studied derivatives, the compounds substituted with CF(3)- at position 2 of phenothiazine ring were the most active membrane perturbants. No clear relation was found between effects exerted by phenothiazine maleates on model membranes and their ability to modulate P-glycoprotein transport activity.     

Soluble Fas (FasB) regulates luteal cell apoptosis during luteolysis in murine ovaries

During luteolysis, luteal cell apoptosis is induced by the Fas ligand (FasL)/Fas system. In murine luteal bodies, we demonstrated the expression of mRNA of soluble form of Fas (FasB), which binds to FasL and prevents apoptosis induction. By in situ hybridization, strong expression of FasB mRNA was observed in normal luteal bodies, in which no apoptotic cells were detected, but negative/trace expression in regressing luteal bodies, in which many apoptotic cells were observed. Immunohistochemical staining revealed that Fas and TNF-alpha were localized in both normal and regressing luteal bodies, but IFN-gamma was localized only in regressing luteal bodies. Apoptosis was induced in primary cultured luteal cells, when they were pretreated with TNF-alpha and IFN-gamma and then incubated with TNF-alpha, IFN-gamma, and mouse recombinant FasL (rFasL). However, no apoptosis was detected in the cells, when they were treated with rFasL alone, TNF-alpha alone, IFN-gamma alone, TNF-alpha and rFasL, IFN-gamma and rFasL, or TNF-alpha and IFN-gamma. Fas mRNA expression in cultured luteal cells was up-regulated by the treatment of TNF-alpha, IFN-gamma, or TNF-alpha and IFN-gamma. The expression of FasB mRNA was down-regulated, when the cells were treated with TNF-alpha and IFN-gamma, but its expression was not changed by the treatment of TNF-alpha alone or IFN-gamma alone. We conclude that FasB inhibits the apoptosis induction in luteal cells of normal luteal bodies, and that decreased FasB production induced by TNF-alpha and IFN-gamma made possible the apoptosis induction in the luteal cells of regressing luteal bodies.     

A kinetic mechanism for the fast movement of Chara myosin

Endoplasmic streaming of characean cells of Nitella or Chara is known to be in the range 30-100 microm/second. The Chara myosin extracted from the cells and fixed onto a glass surface was found to move muscle actin filaments at a velocity of 60 microm/second. This is ten times faster than that of skeletal muscle myosin (myosin II). In this study, the displacement caused by single Chara myosin molecules was measured using optical trapping nanometry. The step size of Chara myosin was approximately 19nm. This step size is longer than that of skeletal muscle myosin but shorter than that of myosin V. The dwell time of the steps was relatively long, and this most likely resulted from two rate-limiting steps, the dissociation of ADP and the binding of ATP. The rate of ADP release from Chara myosin after the completion of the force-generation step was similar to that of myosin V, but was considerably slower than that of skeletal muscle myosin. The 19nm step size and the dwell time obtained could not explain the fast movement. The fast movement could be explained by the load-dependent release of ADP. As the load imposed on the myosin decreased, the rate of ADP release increased. We propose that the interaction of Chara myosin with an actin filament resulted in a negative load being imposed on other myosin molecules interacting with the same actin filament. This resulted in an accelerated release of ADP and the fast sliding movement.     

Zinc-induced sodium-dependent vitamin C transporter 2 expression: potent roles in osteoblast differentiation

Zinc is an essential trace element that increases osteoblast numbers and bone formation. However, the mechanisms involved in the Zn-induced differentiation of osteoblasts are poorly understood. We examined the roles of L-ascorbic acid (AA) and its transporter, sodium-dependent vitamin C transporter (SVCT) 2, in the Zn-induced expression of osteoblastic differentiation markers. Zinc time- and dose-dependently induced SVCT2 mRNA expression in the absence or presence of AA. Western blotting and kinetic assays showed that Zn increased functional SVCT2 protein levels and AA transport. In the presence of AA, 50 microM Zn enhanced mRNA expression of the osteoblastic differentiation markers alkaline phosphatase, alpha(1)(I) procollagen, osteopontin (OPN), and osteocalcin (OCN) by 3.9-, 3.8-, 3.3-, and 3.5-fold, respectively; in the absence of AA, the Zn-induced increase was 2.8-, 2.5-, 1.3-, and 1.1-fold, respectively. These findings suggest that AA and SVCT2 mediate Zn-induced OPN and OCN expression and partly regulate Zn-induced osteoblastic differentiation.     

Somatostatin suppresses ghrelin secretion from the rat stomach

Ghrelin is an acylated peptide that stimulates food intake and the secretion of growth hormone. While ghrelin is predominantly synthesized in a subset of endocrine cells in the oxyntic gland of the human and rat stomach, the mechanism regulating ghrelin secretion remains unknown. Somatostatin, a peptide produced in the gastric oxyntic mucosa, is known to suppress secretion of several gastrointestinal peptides in a paracrine fashion. By double immunohistochemistry, we demonstrated that somatostatin-immunoreactive cells contact ghrelin-immunoreactive cells. A single intravenous injection of somatostatin reduced the systemic plasma concentration of ghrelin in rats. Continuous infusion of somatostatin into the gastric artery of the vascularly perfused rat stomach suppressed ghrelin secretion in both dose- and time-dependent manner. These findings indicate that ghrelin secretion from the stomach is regulated by gastric somatostatin.     

New phenothiazine-type multidrug resistance modifiers: anti-MDR activity versus membrane perturbing potency

The phenothiazine multidrug resistance (MDR) modulators are chemically diversified but share the common feature to be hydrophobic cationic molecules. Molecular mechanisms of their action may involve interactions with either P-glycoprotein or membrane lipid matrix. In the present work we study the anti-MDR and biophysical membrane effects of new phenothiazine derivatives differing in the type of group substituting phenothiazine ring at position 2 (H-, Cl-, CF(3)-) and in the side chain group (NHCO(2)CH(3) or NHSO(2)CH(3)). Within each phenothiazine subset we found that anti-MDR activity (determined by P-glycoprotein inhibition assessed by flow cytometry) correlates with the theoretically calculated hydrophobicity value (logP) and experimental parameters (determined by calorimetry and fluorescence spectroscopy) of lipid bilayers. It is concluded that the biological and biophysical activity of phenothiazine derivatives depends more on the type of ring substitution than on the nature of the side chain group.