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Biomedical subjects

A Ikegami

Publications and source records attributed to A Ikegami.

At least 19 recordsLinked to original sources
PubMed1992

Vitamin K2 modulates proliferation and function of osteoblastic cells in vitro.

A human osteosarcoma cell line, HOS TE85 cells, and a mouse osteoblastic cell line, MC3T3-E1 cells, were cultured for 3 days in a medium containing various concentrations of menaquinone-4 (vitamin K2). As a result, the proliferation of HOS cells was suppressed by vitamin K2 in a dose dependent manner up to 56% of control by 10(-7)M of vitamin K2 and that of MC3T3-E1 cells was suppressed to 84% of control by 10(-6)M of vitamin K2. Vitamin K2 increased alkaline phosphatase activity in both kinds of cells. Warfarin counteracted the effect of vitamin K2 on osteoblastic cell proliferation. Our results show that vitamin K2 modulates proliferation and function of osteoblastic cells by some mechanisms including gamma-carboxylation system.

Animals↗
PubMed1992

[Hemorheological effect of KB-2796, a new Ca2+ antagonist].

The hemorheological effect of KB-2796, 1-[bis(4-fluorophenyl)methyl]-4-(2,3,4,-trimethoxybenzyl)piperazine dihydrochloride, was studied in guinea pigs and rabbits in comparison with those of flunarizine (FNZ) and pentoxifylline (PXF). KB-2796 and FNZ at 10-100 microM dose-dependently prevented crenation of rabbit erythrocytes induced by the Ca2+ ionophore A23187. After incubation of guinea pig whole blood at 37 degrees C, blood micropore-filterability decreased and blood viscosity increased with the progress of erythrocyte crenation. After a 4-hr incubation, KB-2796 inhibited erythrocyte crenation and decreased blood filterability at a concentration of 30 microM, and it increased blood viscosity at 10 microM. Treatment with FNZ (30 microM) and PXF (100 microM) also inhibited erythrocyte crenation and decreased blood filterability. Intravenous administration of KB-2796 at 3 mg/kg significantly inhibited the decrease of blood micropore-filterability after occlusion of the bilateral carotid arteries in rabbits. Although FNZ (3 mg/kg, i.v.) had no effect, PXF (3 mg/kg, i.v.) produced significant inhibition. These results suggest that KB-2796 prevents increase of blood viscosity and decrease of blood filterability by inhibiting the crenation of erythrocytes and suggest that this effect may be useful for the improvement of hemorheology in ischemic disease.

Animals↗
PubMed1992

Neurochemical investigation on the effects of a new diphenylpiperazine calcium antagonist, KB-2796, on the central dopaminergic system of rats.

The effects of KB-2796, a new diphenylpiperazine calcium antagonist, on the striatal dopaminergic system of rats were investigated in comparison with various calcium antagonists and the dopamine antagonist chlorpromazine. The inhibiting effect of KB-2796 on [3H]spiperone binding to striatal membranes in vitro was weaker than those of chlorpromazine and the other diphenylpiperazine analogues, flunarizine and cinnarizine, and more potent than those of verapamil and nicardipine. Diltiazem and nifedipine were inactive. KB-2796 (30, 100 mg/kg, p.o.) had no effect on Kd and Bmax values of in vitro [3H]spiperone specific binding to striatal membranes obtained from the rat at 36 hr and 7 days after repeated administration for 18 days, whereas flunarizine (30 mg/kg, p.o.) and chlorpromazine (3 mg/kg, p.o.) increased Bmax values by 47% and 31%, respectively, at 36 hr, but not at 7 days after the final administration. At 1 hr after the single administration, KB-2796 (30, 100 mg/kg, p.o.) had no effect on the content of dopamine and its metabolites in the striatum, whereas flunarizine (30 mg/kg, p.o.) and chlorpromazine (3 mg/kg, p.o.) increased the level of homovanillic acid. These results indicate that flunarizine may affect dopaminergic neurotransmission by partially blocking dopamine D2 receptors, while KB-2796 has negligible in vivo effect on the dopaminergic system.

Animals↗
PubMed1992

[Immunohistochemical study of collagen type III in adenomyosis].

To clarify the mechanism of the origin of adenomyosis, we investigated the immunohistochemical distribution of collagen type III in the human endometrium and the adenomyosis throughout the menstrual cycle. 1) Collagen type III was localized in the stroma of normal endometrium and ectopic endometrium, and in the myometrium. No staining of collagen type III was observed in the endometrial gland. 2) The intensity of staining for collagen type III in the basal layer of normal endometrium was stronger than those in the functional layer. The staining in the proliferative phase was stronger than that in the secretory phase. 3) The intensity of staining of collagen type III in ectopic endometrium paralleled that in the basal layer of normal endometrium. 4) The intensity of staining of collagen type III in the myometrium did not change throughout the menstrual cycle. These results suggest that close similarities exist between stromal cells in normal endometrium and in ectopic endometrium from the viewpoint of the extracellular matrix.

Collagen↗
PubMed1991

Behavioral and biochemical effects of a novel calcium antagonist, KB-2796, on the central dopaminergic system.

The effect of a novel calcium antagonist, KB-2796, on the central dopaminergic system was behaviorally and biochemically studied in mice and compared with that of flunarizine, nicardipine and chlorpromazine. Neither KB-2796 nor nicardipine had an inhibitory effect on apomorphine-induced cage climbing and turning behavior in mice with unilateral lesions in the striatum, even at a high dose of 100 mg/kg p.o. Both drugs slightly inhibited methamphetamine-induced increases in locomotor activity and turning behavior but only at a high dose (100 mg/kg p.o.). KB-2796 and nicardipine did not affect the content of dopamine (DA), norepinephrine, and serotonin, or the content of their metabolites homovanillic acid (HVA), dihydroxyphenylacetic acid (DOPAC), and 5-hydroxyindoleacetic acid, or the DA turnover rate in the forebrain of mice. However, flunarizine and chlorpromazine inhibited behavioral changes induced by apomorphine or methamphetamine in a dose-dependent manner, increased the content of DOPAC and HVA and accelerated the DA turnover rate in mouse brain. These results suggest that KB-2796 has a negligible effect on the central dopaminergic system.

Animals↗
PubMed1990

Effect of partial delipidation of purple membrane on the photodynamics of bacteriorhodopsin.

The effect of lipid-protein interaction on the photodynamics of bacteriorhodopsin (bR) was investigated by using partially delipidated purple membrane (pm). When pm was incubated with a mild detergent, Tween 20, the two major lipid components of pm, phospholipids and glycolipids, were released in different ways: the amount of phospholipids released was proportional to the logarithm of the incubation time; the release of glycolipids became noticeable after the release of approximately 2 phospholipids/bR, but soon leveled off at approximately 50% of the initial content. It was found that the thermal decay of the photocycle intermediate N560 was inhibited by the removal of less than 2 phospholipids per bR. This inhibition was partly explained by an increase in the local pH near the membrane surface. More significant changes in the bR photoreactions were observed when greater than 2 phospholipids/bR were removed: (1) the extent of light adaptation became much smaller, and this reduction correlated with the release of glycolipids; (2) N560 became difficult to detect; (3) the M412 intermediate, which is characterized by a pH-insensitive lifetime, was replaced by a long-lived M-like photoproduct with a pH-sensitive lifetime. The heavy delipidation apparently altered the mechanism by which the deprotonated Schiff base receives a proton. An important conformational change in the protein moiety is suggested to take place during the M412 state, this conformational change being inhibited in the rigid lipid environment.

Bacteriorhodopsins↗
PubMed1989

Independent flexible motion of submolecular domains of the Ca2+,Mg2+-ATPase of sarcoplasmic reticulum measured by time-resolved fluorescence depolarization of site-specifically attached probes.

The Ca2+-transporting ATPase of rabbit skeletal muscle sarcoplasmic reticulum was site-specifically labeled with either N-(1-anilinonaphth-4-yl)maleimide (ANM) or 5-[[(iodoacetamido)-ethyl]amino]naphthalene-1-sulfonate (IAEDANS), and the segmental motion of submolecular domains of the ATPase molecule was examined by means of time-resolved and steady-state fluorescence anisotropy measurements. The ANM-binding domain showed wobbling with a rotational relaxation time phi = 69 ns in the absence of free Ca2+ without any independent wobbling of the ANM moiety. The IAEDANS-binding domain showed a significantly slower wobbling with phi = 190 ns in the absence of Ca2+. The present results demonstrated for the first time that the ATPase molecule is composed of distinct domains whose mobilities are considerably different from each other. The binding of Ca2+ to the transport site increased the segmental motion of ANM-labeled domain, leading to a phi value of 65 ns. Solubilization of the ANM-labeled SR membranes by deoxycholate led to a further increase in the segmental flexibility (phi = 48 ns in the absence of free Ca2+), indicating that the mobility of the ANM-binding domain was considerably restricted through interaction with the membrane. The mobility of the ANM-binding domain of solubilized ATPase was also increased to some extent upon binding of Ca2+.

Adenosine Triphosphatases↗
PubMed1989

Correlation between internal motion and emission kinetics of tryptophan residues in proteins.

Time-resolved fluorescence anisotropy measurements of tryptophan residues were carried out for 44 proteins. Internal rotational motion with a sub-nanosecond correlation time (0.9 +/- 0.6 ns at 10 degrees C) was seen in a large number of proteins, though its amplitude varied from protein to protein. It was found that tryptophan residues which were almost fixed within a protein had either a long (greater than 4 ns) or short (less than 2 ns) fluorescence lifetime, whereas a residue undergoing a large internal motion had an intermediate lifetime (1.5-3 ns). It is suggested that the emission kinetics of a tryptophan residue is coupled with its internal motion. In particular, an immobile tryptophan residue emitting at long wavelength was characterized by a long lifetime (greater than 4 ns). It appears that a tryptophan residue fixed in a polar region has little chance of being quenched by neighboring groups.

Fluorescence Polarization↗
PubMed1989

Orientation of retinal in purple membrane determined by polarized Raman spectroscopy.

The orientation of the retinal molecule in the purple membrane was determined by polarized Raman spectroscopy for stacked purple membranes. The depolarization ratios of C = C stretching vibration mode were measured for three scattering geometries of purple membrane films. From the depolarization ratios we estimated the tilt angle of the transition dipole moment of retinal to the membrane normal and the rotational angle of the molecular plane along the transition dipole moment of retinal. The molecular plane of M intermediate was found to be almost perpendicular to the membrane plane. We confirmed that the tilt angle was 65 +/- 2 degrees for both bR and M intermediates.

Bacteriorhodopsins↗
PubMed1989

[Effect of trazodone (KB-831) and its metabolites on brain monoamines in rat].

The effects of trazodone (KB-831) and its metabolites on the uptake, turnover and contents of monoamines in rats were studied in comparison with those of imipramine and mianserin. Trazodone exhibited a more potent inhibitory effect on the uptake of [3H] 5-hydroxytryptamine (5-HT) into brain synaptosomes than on the uptake of [3H]norepinephrine (NE). Trazodone at 10-30 mg/kg, p.o., also inhibited the p-chloramphetamine-induced depletion of 5-HT in rat brain, but not the 6-hydroxydopamine-induced NE depletion in rat heart. Trazodone was the most selective 5-HT uptake inhibitor among the drugs tested in vitro. Its metabolite, m-chlorophenyl-piperazine (m-CPP), inhibited 5-HT and NE uptake in vitro, but not in vivo. Trazodone (100 mg/kg) and imipramine (30-100 mg/kg) inhibited the depletion of NE induced by alpha-methyl-p-tyrosine, whereas mianserin (100 mg/kg) facilitated it. At 1 hr after a single administration of each drug, an increase in 5-HT content and a decrease in 5-hydroxyindole-3-acetic acid (5-HIAA) content were observed when 30 mg/kg trazodone was used. At 100 mg/kg, trazodone increased the levels of dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) and decreased the NE content. m-CPP (10-30 mg/kg) produced similar effects on monoamine contents to those of trazodone. Imipramine and mianserin had no effect on monoamine contents even at a dose of 100 mg/kg. After 3 weeks of successive administration, an increase in 5-HT and a decrease in 5-HIAA were induced by trazodone and m-CPP at 1 hr, but not at 17 hr, after the final administration. Imipramine decreased the contents of NE and 5-HIAA, and its effects lasted for 17 hr. These results suggest that trazodone is a selective 5-HT uptake inhibitor and that its neurochemical profile is different from those of imipramine and mianserin.

Animals↗
PubMed1988

Bacteriorhodopsin photoreaction: identification of a long-lived intermediate N (P,R350) at high pH and its M-like photoproduct.

An alkaline suspension of light-adapted purple membrane exposed to continuous light showed a large absorption depletion at 580 nm and a small increase around 350 nm. We attribute this absorption change to an efficient photoconversion of bR570 into a photoproduct N (P,R350), which has a major absorption maximum between 550 and 560 nm but has lower absorbance than bR570. N was barely detectable at low pH, low ionic strength, and physiological temperature. However, when the thermal relaxation of N to bR570 was inhibited by increasing pH, increasing ionic strength, and decreasing temperature, its relaxation time could be as long as 10 s at room temperature. N is also photoactive; when it is present in significant concentrations, e.g., accumulated by background light, the flash-induced absorption changes of purple membrane suspensions were affected. Double-excitation experiments showed an M-like photoproduct of N,NM, with an absorption maximum near 410 nm and a much longer lifetime than M412. It may be in equilibrium with an L-like precursor NL. We suggest that N occurs after M412 in the photoreaction cycle and that its photoproduct NM decays into bR570. Thus, at high pH and high light intensity, the overall photoreaction of bR may be approximated by the two-photon cycle bR570----M412----N----(NL----NM)----bR570, whereas at neutral pH and low light intensity it can be described by the one-photon cycle bR570----M412----N----O640----bR570.(ABSTRACT TRUNCATED AT 250 WORDS)

Bacteriorhodopsins↗
PubMed1988

Structure and function of bacteriorhodopsin.

Bacteriorhodopsin (bR) is a powerful light-driven proton pump. We have developed a procedure to prepare bR-containing membrane vesicles in which a pH gradient as large as 4 pH units can be generated and maintained in the light. Using such a system, we have demonstrated that bR exhibits a high proton pump activity in a wide pH region; it works well at least between pH 4 and 9.5. For the large light-induced pH change in the external medium, the presence of a high concentration (approximately 0.1 M) of magnesium or transition metal ion is required. It is suggested that the influx of magnesium ion, electrically coupled with the proton release, takes place in the light. The three-dimensional structure of bR was studied by fluorescence energy transfer techniques. It was shown that the retinal chromophore is located 10 A below a surface of purple membrane. The in-plane location and orientation of retinal was also determined; it exists in a pocket surrounded by the helices 3, 4, 5, and 6. The position of a fluorescent probe labeled to Lys 41 was determined to be near the helix 7. Based on the results obtained, we propose a model of the bR structure. The dynamic structure of bR was investigated by fluorescence depolarization techniques. It was shown that the retinal chromophore is tightly buried in a pocket within the protein. In the presence of detergents like octylglucoside, its tertiary structure can be stable near the electric isosbestic point. The rate of dissociation/association process of bR molecules is sensitive to the pH of the medium. Dimeric and/or trimeric bR can exist stably if the concentration of detergent and other solvent conditions are adequately controlled. The photoreaction of bR in purple membrane, including the dark/light adaptation, the trans photocycle and the primary photoreaction, was reported. With respect to the trans photocycle, we found that, at alkaline pH, an M-like photoproduct (NM) is generated by excitation of a long-lived photoproduct N560 which has a major absorption maximum near 560 nm. We suggest that, at alkaline pH, the overall photoreaction of bR under steady illumination is approximated by the two-photon cycle: bR570 approximately greater than M412----N560 approximately greater than NM----bR570. With respect to the primary photoreaction, we found that the fluorescence quantum yield of the near-infrared emission of bR was greatly enhanced at acidic pH (approximately pH 2).(ABSTRACT TRUNCATED AT 400 WORDS)

Bacteriorhodopsins↗
PubMed1988

Electroporation of cell membrane visualized under a pulsed-laser fluorescence microscope.

Controlled permeability can be conferred to cell membranes by exposing cells to a microsecond electric pulse of sufficient intensity (electroporation). By constructing a fluorescence microimaging system with a submicrosecond time resolution we have been able to resolve temporally and spatially the events in a single cell under a microsecond electric pulse. An enormous membrane conductance, corresponding to a loss of 0.01-0.1% of the membrane area, was observed in those membrane regions where the transmembrane potential induced by the electric pulse exceeded a critical value. The conductance decreased to a low level in a submillisecond after the pulse, leaving a moderately electroporated cell.

Animals↗
PubMed1988

Optical anisotropy decay studies of the dynamic structure of myosin filaments.

We applied flash-induced absorption and phosphorescence anisotropy decay methods to the study of rotational motions of myosin heads in solution), myofibrils and muscle fibers); myosin heads were selectively labeled with a triplet probe EMI (5-eosinylmaleimide). EMI-labeled subfragment 1 (S1) showed a single exponential decay of anisotropy over two decades; the analysis indicated that if S1 is modeled as a prolate ellipsoid of revolution, the major axis was 16-17 nm and the minor axis 4.7-4.5 nm. The decay curve of myosin filaments could be simulated by double-exponentials-plus-constant approximation. The data could be analyzed by a double-cone model), in which we assumed that a head part (S1), wobbles in the first cone and a rod portion next to the head also wobbles in the second cone. The semiangle of each cone was estimated to be 35 and 48 degrees, respectively. We found that myosin heads in myofibrils under relaxing conditions extensively rotated as in myosin filaments in solution. When the spacing between thick and thin filaments was artificially reduced by the increase of osmotic pressure with the addition of polyvinylpyrrolidone (PVP), restriction of the angular range of the rotational motion was observed. Under rigor conditions no motion was observed in a 10 microsecond time scale, indicating that the heads were immobilized by binding to thin filaments. Preliminary results on the rotational motions of myosin heads in muscle fibers are also reported.

Animals↗