Biomedical subjects

Hiroaki Yokota

Publications and source records attributed to Hiroaki Yokota.

11 recordsLinked to original sources

PubMed2006

Dynamic polymorphism of actin as activation mechanism for cell motility.

Actin filament dynamics are crucial in cell motility. Actin filaments, and their bundles, networks, and gels assemble and disassemble spontaneously according to thermodynamic rules. These dynamically changing structures of actin are harnessed for some of its functions in cells. The actin systems respond to external signals, forces, or environments by biasing the fluctuation of actin assembly structures. In this study, dynamic conformation of actin molecules was studied by monitoring conformational dynamics of actin molecules at the single molecule level in real time. Actin conformation spontaneously fluctuates between multiple conformational states. Regarding myosin motility, the dynamic equilibrium of actin conformation was interpreted as between states that activates and inhibits the motility. The binding of myosin to actin filaments activates myosin motility by shifting the conformational fluctuation of actin towards the state that activates the motility. Thus, the activation mechanism based on thermal fluctuation is suggested at molecular level as well as at cellular level.

Actins↗

PubMed2006

Dynamic polymorphism of Ras observed by single molecule FRET is the basis for molecular recognition.

Ras regulates signal transduction pathway function by dynamically interacting with various effectors. To understand the basis for Ras function, its conformational dynamics were measured in the absence and presence of effectors using single molecule fluorescence resonance energy transfer (FRET) between probes located on the Switch II region and GTP. The time trajectories of FRET efficiency from GTP-bound Ras showed that this conformation spontaneously varies among multiple states. Among them, a low FRET state was identified as an inactive state. The transition involving the inactive conformational state occurred in the time range of seconds. In contrast, fluctuation occurring most probably between multiple active high FRET conformational states lasted approximately 30 ms but converged to a specific conformational state upon binding to an effector. Thus, Ras conformation spontaneously fluctuates to readily interact with various effectors.

Fluorescence Resonance Energy Transfer↗

PubMed2006

Dynamic polymorphism of single actin molecules in the actin filament.

Actin filament dynamics are critical in cell motility. The structure of actin filament changes spontaneously and can also be regulated by actin-binding proteins, allowing actin to readily function in response to external stimuli. The interaction with the motor protein myosin changes the dynamic nature of actin filaments. However, the molecular bases for the dynamic processes of actin filaments are not well understood. Here, we observed the dynamics of rabbit skeletal-muscle actin conformation by monitoring individual molecules in the actin filaments using single-molecule fluorescence resonance energy transfer (FRET) imaging with total internal reflection fluorescence microscopy (TIRFM). The time trajectories of FRET show that actin switches between low- and high-FRET efficiency states on a timescale of seconds. If actin filaments are chemically cross-linked, a state that inhibits myosin motility, the equilibrium shifts to the low-FRET conformation, whereas when the actin filament is interacting with myosin, the high-FRET conformation is favored. This dynamic equilibrium suggests that actin can switch between active and inactive conformations in response to external signals.

Actin Cytoskeleton↗

PubMed2006

Effect of a caries-detecting solution on the tensile bond strength of four dentin adhesive systems.

This study investigated the effect of a caries-detecting solution on the tensile bond strength (TBS) to sound bovine dentin--which was either rinsed thoroughly of or contaminated with the caries-detecting solution. Caries Detector (1.0% acid red in propylene glycol) was applied on flat dentin surfaces for 10 seconds, rinsed, and dried with syringe air. In another group, Caries Detector was not rinsed but air-dried. Then, the surfaces were treated with one of the following adhesive systems: Clearfil Protect Bond, Clearfil SE Bond, One-Up Bond F, or Single Bond. Furthermore, an ingredient of Caries Detector, either 1.0% acid red aqueous solution or propylene glycol, was applied to evaluate the effect of each component. In the control groups, Caries Detector was not applied to the dentin surfaces. Finally, a resin composite was light-cured and the TBS measured. Fractured specimens and treated dentin surfaces were observed by SEM. Caries Detector did not reduce the tensile bond strength of any adhesive system (p>0.05) when rinsed thoroughly. On the other hand, when dentin surface was contaminated with Caries Detector, TBS decreased significantly with Clearfil SE Bond and Single Bond. As for the ingredients of Caries Detector, the effect of acid red on TBS was not significant, but that of propylene glycol was significant.

Adhesives↗

PubMed2005

Five-year clinical evaluation of two adhesive systems in non-carious cervical lesions.

OBJECTIVE: This controlled clinical trial evaluated the 5-year clinical performance of a self-etching primer system including selective enamel-etching with phosphoric acid and a one-bottle adhesive system. METHODS: Seventy-two non-carious cervical lesions in 8 patients (4 male and 4 female) with a mean age of 61.3 years (range 45-78) participated in the study. An enamel bevel was placed and dentin lightly ground, and cavities restored with clearfil liner bond II (LB) or single bond (SB) in conjunction with a hybrid resin composite (Clearfil AP-X). In the case of 27 cavities for LB, the enamel was pretreated with 37% phosphoric acid for 10 s. Each patient received both types of restoration, which were distributed on a random basis. All restorations (37 restorations for LB and 35 restorations for SB) were placed by one dentist. The restorations were evaluated blind after 5 years using modified USPHS criteria. The data were statistically analyzed using the Fisher's exact test. RESULTS: All but one restoration (which was replaced by a crown after the 2-year recall) were evaluated after 5 years. 100% retention rates were recorded for both restorative groups. No caries was detected in association with any restorations. The only minor problem was marginal discoloration; superficial and localized marginal discoloration occurred around 18% of the restorations, and mainly at the dentin margin. There were no significant differences in the marginal integrity between the LB and SB groups. CONCLUSIONS: Restorative materials used in this study demonstrated a good clinical effectiveness in the restoration of non-carious cervical lesions for 5 years.

Aged↗

PubMed2004

The effect of light-curing modes on the microleakage of cervical resin composite restorations.

OBJECTIVE: This study investigated the effect of light-curing modes on the microleakage of cervical resin composite restorations. METHODS: Eighty wedge-shaped cervical cavities, C-factor approximately 1.3, were prepared on the labial surface of bovine incisors. The cavities were treated with a two-step experimental self-etching primer adhesive system containing an antibacterial monomer (ABF), according to the manufacturer's instructions, and filled with a single increment of a hybrid resin composite. The restorations were allocated randomly into four groups of 20: Group 1-the restorations were light-cured for 40 s with a conventional light-curing unit (New Light VL-II); Group 2-the restorations were cured with Candelux using a two-step mode; Group 3-the restorations were cured with Astralis 7 using a ramping mode; Group 4-the restorations were light-cured for 3 s with a plasma arc light-curing unit (Wave Light). Half of the specimens from each group were subjected to thermocycling (5-60 degrees C, 15 s dwell time, 5000 cycles) prior to immersion in 0.5% basic fuchsin. The teeth were sectioned and the degrees of dye penetration were scored. The data were analyzed with either the Kruskal-Wallis test or the Mann-Whitney U-test (p < 0.05) RESULTS: No significant differences were found in the microleakage scores among the light-curing modes used. The restorations tended to display more microleakage when they were subjected to thermocycling, but the differences were not statistically significant. CONCLUSIONS: These findings suggest that light-curing modes may have no effect on the microleakage of cervical cavities with a small C-factor, as is the case in this study.

Animals↗

PubMed2004

Single-molecule imaging of the dynamic interactions between macromolecules.

In recent years, the development of single-molecule detection techniques has allowed the dynamic properties of biomolecules, which are normally obscured in conventional ensemble measurements, to be measured. One of these single-molecule detection techniques allows the measurement of dissociation and association events of individual molecules to be measured. This technique is based on the unique premise that the mobility between molecules that are bound and the mobility between those that are free in solution are different. The binding of ATP at the beginning and its dissociation at the end of the hydrolysis reaction were detected at the single-molecule level in real time. In this study, we extended this technique to image the dynamic interactions between large biomolecules (protein/protein and protein/polysaccharide). The binding and dissociation of fluorescently labeled macromolecules to partner molecules fixed on a glass surface were visualized by total internal reflection fluorescence microscopy. The dynamic interactions between the proteins in two energy conversion systems, that is, signaling proteins and enzyme molecules moving on dextran, have been measured. In these systems, the dynamic interactions were sensitive to the factors determining the chemical reactions. Thus, the dynamic interactions monitored in the single-molecule measurements provided useful information to further the understanding of the underlying mechanisms of energy conversion systems.

Adenosine Triphosphate↗

PubMed2004

Bond durability of resin cements to Au-Pd-Ag alloy under cyclic impact load.

The bond durability of resin cements to a 12% Au-Pd-Ag alloy was studied through cyclic impact tests with different loads. A piece of casting alloy was bonded to a cast block with two types of resin cements, Super Bond C&B and Bistite II. A shear load was applied onto a small piece of alloy until debonding of the specimen, using different weights of plungers, 130 g, 230 g, 330 g and 430 g. The specimen bonded with Super Bond exhibited a higher resistance than that with Bistite II. The fracture modes of the debonded cements were completely different from each other. That is, Bistite II showed a bulk fracture of cement by the crack penetrating through the cement layer. On the other hand, Super Bond showed damages limited to the surface and no bulk fracture. The mode of fracture was dependent not on the loading weight but the types of resin cements used.

Analysis of Variance↗

PubMed2004

Microleakage of cervical cavities restored with flowable composites.

PURPOSE: To investigate the microleakage of cervical cavities restored with flowable composites in conjunction with an all-in-one adhesive system (AQ Bond) and an experimental two-step self-etching primer system (ABF) after thermocycling or flexural load cycling. METHODS: 180 wedge-shaped cervical cavities on the labial surfaces of bovine incisors were treated with AQ Bond or ABF according to the manufacturers' instructions. The treated cavities were filled with one of three flowable composites (AElite Flo, Metafil Flo or Protect Liner F). Ten of 30 specimens for each group were immersed in 0.5% basic fuchsin solution immediately after finishing of the restorations. Specimens to be subjected to thermocycling (5-60 degrees C, 15 seconds dwell time, 5000 cycles) or to flexural load cycling (approximately 0.5 mm labio-lingual displacement at the incisal edge, 10,000 cycles, 1 Hz) prior to immersion in the dye were also prepared. After 24-hour storage in the dye solution, the teeth were sectioned longitudinally through the center of the restorations, and the degrees of dye penetration scored. The microleakage scores of a hybrid composite (Clearfil AP-X) obtained from our previous study were used for comparison. The data were analyzed with the Kruskal-Wallis test and the Mann-Whitney U-test (P < 0.05). RESULTS: No significant differences in the microleakage patterns and scores were found among the flowable composites. On the other hand, significant differences in the microleakage patterns and scores were observed between the flowable and the hybrid composites. Thermocycling caused deterioration of marginal integrity, and the flowable composites showed more microleakage than the hybrid composite. In contrast, flexural load cycling did not cause deterioration of the marginal integrity when the cavities were filled with the flowable composites. Statistical analysis also revealed that the adhesive systems played a large role in the microleakage patterns.

Animals↗

PubMed2003

Monitoring molecular beacon DNA probe hybridization at the single-molecule level.

We have monitored the reaction dynamics of the DNA hybridization process on a liquid/solid interface at the single-molecule level by using a hairpin-type molecular beacon DNA probe. Fluorescence images of single DNA probes were recorded by using total internal reflection fluorescence microscopy. The fluorescence signal of single DNA probes during the hybridization to individual complementary DNA probes was monitored over time. Among 400 molecular beacon DNA probes that we tracked, 349 molecular beacons (87.5 %) were hybridized quickly and showed an abrupt fluorescence increase, while 51 probes (12.5 %) reacted slowly, resulting in a gradual fluorescence increase. This ratio stayed about the same when varying the concentrations of cDNA in MB hybridization on the liquid/surface interface. Statistical data of the 51 single-molecule hybridization images showed that there was a multistep hybridization process. Our results also showed that photostability for the dye molecules associated with the double-stranded hybrids was better than that for those with the single-stranded molecular beacon DNA probes. Our results demonstrate the ability to obtain a better understanding of DNA hybridization processes using single-molecule techniques, which will improve biosensor and biochip development where surface-immobilized molecular beacon DNA probes provide unique advantages in signal transduction.

Biosensing Techniques↗

PubMed2003

Effect of low-viscosity resin-based composite on the microleakage of cervical restorations.

PURPOSE: To investigate the effect of a low-viscosity resin-based composite (LVC) liner on the microleakage of cervical resin-based composites bonded with new adhesive systems. METHODS: 180 wedge-shaped cervical cavities on bovine incisors were treated with AQ Bond (all-in-one), ABF (experimental two-step self-etching primer containing antibacterial monomer) or Clearfil SE Bond (two-step self-etching primer) systems according to the manufacturers' instructions. Half of the treated cavities in each adhesive system were lined with an LVC (Protect Liner F) and filled with a hybrid resin-based composite (Clearfil AP-X). Ten specimens from each group were immersed in 0.5% basic fuchsin solution immediately after finishing the restorations. The specimens to be subjected to thermocycling (5-60 degrees C, 15 seconds dwell time, 5,000 cycles) or to flexural load cycling (approximately 0.5 mm labio-lingual displacement at the incisal edge, 10,000 cycles, 1 Hz) prior to immersion in the dye solution were also prepared. The teeth were sectioned through the center of the restorations and the degrees of dye penetration were scored. The data were analyzed with the Mann-Whitney U-test or the Kruskal-Wallis test (P < 0.05). RESULTS: The use of the LVC liner significantly improved marginal sealing of AQ Bond. However, the LVC liner could not prevent the deterioration in the marginal integrity caused by thermocycling or flexural load cycling. In the case of ABF, the use of the LVC liner showed a trend toward less microleakage. For Clearfil SE Bond, the LVC liner prevented the deterioration in the marginal seal caused by thermocycling.

Animals↗