Biomedical subjects

Hirofumi Shimizu

Publications and source records attributed to Hirofumi Shimizu.

10 recordsLinked to original sources

PubMed2006

Surface structure and its dynamic rearrangements of the KcsA potassium channel upon gating and tetrabutylammonium blocking.

KcsA is the first potassium channel for which the molecular structure was revealed. However, the high resolution structural information is limited to the transmembrane domain, and the dynamic picture of the full KcsA channel remains unsolved. We have developed a new approach to investigate the surface structure of proteins, and we applied this method to investigate the full length of the KcsA channel. Single-cysteine substitution was introduced into 25 sites, and specific reaction of these mutated channels to a bare surface of a flat gold plate was evaluated by surface plasmon resonance measurements. The surface plasmon resonance signals revealed the highest exposure for the mutant of the C-terminal end. When the gate of the KcsA channel is kept closed at pH 7.5, the extent of exposure showed periodic patterns for the consecutive sites located in the cytoplasmic (CP) and N-terminal domain. This suggests that these stretches take the alpha-helical structure. When the channel was actively gated at pH 4.0, many sites in the CP domain became exposed. Compared with the rigid structure in pH 7.5, these results indicate that the CP domain became loosely packed upon active gating. The C-terminal end of the M2 helix is a moving part of the gate, and it is exposed to the outer surface slightly at pH 4.0. By adding a channel blocker, tetrabutylammonium, the gate is further exposed. This suggests that in the active gating tetrabutylammonium keeps the gate open rather than being trapped in the central cavity.

Bacterial Proteins↗

PubMed2006

Testing response-stimulus equivalence relations using differential responses as a sample.

This study tested the notion that an equivalence relation may include a response when differential responses are paired with stimuli presented during training. Eight normal adults learned three kinds of computer mouse movements as differential response topographies (R1, R2, and R3). Next, in matching-to-sample training, one of the response topographies was used to select a comparison stimulus B (B1, B2, or B3) conditionally upon presentation of sample stimulus A (A1, A2, or A3), and to select stimulus D (D1, D2, or D3) conditionally upon presentation of stimulus C (C1, C2, or C3). After two sample-comparison-response relations (ABR and CDR) were established, 18 sample-comparison relations were tested (BA, DC, RA, RB, RC, RD, AC, CA, AD, DA, BC, CB, BD, DB, AA, BB, CC, and DD). In the RA, RB, RC, and RD tests, the differential responses (R1, R2, and R3) were used as sample stimuli. All subjects made class-consistent comparison selections in the tests. This study provides evidence that responses may become members of an equivalence class.

Adult↗

PubMed2005

Programmed Instruction to teach pointing with a computer mouse in preschoolers with developmental disabilities.

Programmed Instruction combined with experimenter-provided prompts (physical, verbal, and gesturing) was used to teach pointing with a computer mouse. Three preschoolers who scored at least 1 year below their chronological age levels participated. During the pre-assessment, none of the participants demonstrated pointing. However, they could press and release the mouse button. Programmed Instruction consisted of three stages, based on an analysis of the behavioral prerequisites for pointing. Stage 1 was designed to teach participants to move the mouse. Stage 2 was designed to teach participants to move the on-screen cursor onto specific items on the screen. Stage 3 was designed to teach participants to click on specific items on the screen. Experimenter-provided prompts were used to facilitate skill acquisition at each stage. The post-assessment showed that all participants learned pointing after intervention. The intervention package consisting of Programmed Instruction and experimenter-provided prompts was effective for teaching the hand-eye coordination required for pointing.

Child, Preschool↗

PubMed2005

Paradoxical inhibition of protein aggregation and precipitation by transglutaminase-catalyzed intermolecular cross-linking.

Cross-linking of proteins catalyzed by tissue transglutaminase has been suggested to play key roles in a variety of cellular events, including cell apoptosis and human pathogenesis (e.g. polyglutamine and Alzheimer diseases). It has often been suggested that tissue transglutaminase enhances aggregation and precipitation of damaged or pathogenic proteins. To ascertain whether this is accurate, we investigated the effects of tissue transglutaminase-catalyzed modulation on the aggregation of structurally damaged and unfolded proteins. Our results indicated that the aggregation and precipitation of some unfolded proteins were inhibited by transglutaminasecatalyzed reaction, although the effect was strongly dependent upon the target protein species. To elucidate the molecular events underlying the inhibitory effect, extensive analysis was performed with regard to reduced beta-lactoglobulin using a number of techniques, including chromatography and spectroscopy. The results indicated that cross-linking yields high molecular weight soluble polymers but inhibits the growth of insoluble aggregates. The cross-linked beta-lactoglobulin retained stable secondary structures with a hydrophobic core. We concluded that the transglutaminase-catalyzed intermolecular cross-linking did not necessarily enhance protein aggregation but could sometimes have a suppressive effect. The results of the present study suggested that tissue transglutaminase modifies aggregation and deposition of damaged or pathogenic proteins in vivo in a wide variety of manners depending on the target protein species and solution conditions.

Animals↗

PubMed2005

Coupled K+-water flux through the HERG potassium channel measured by an osmotic pulse method.

The streaming potential (V(stream)) is a signature feature of ion channels in which permeating ions and water molecules move in a single file. V(stream) provides a quantitative measure of the ion and water flux (the water-ion coupling ratio), the knowledge of which is a prerequisite for elucidating the mechanisms of ion permeation. We have developed a method to measure V(stream) with the whole-cell patch-clamp configuration. A HEK293 cell stably expressing the HERG potassium channel was voltage clamped and exposed to hyperosmotic solutions for short periods of time (<1 s) by an ultrafast solution switching system (the osmotic pulse [quick jump-and-away] method). The reversal potentials were monitored by a series of voltage ramps before, during, and after the osmotic pulse. The shifts of the reversal potentials immediately after the osmotic jump gave V(stream). In symmetrical K+ solutions (10 mM), the V(stream)s measured at different osmolalities showed a linear relationship with a slope of -0.7 mV/DeltaOsm, from which the water-ion coupling ratio (n, the ratio of the flux of water to the flux of cations; Levitt, D.G., S.R. Elias, and J.M. Hautman. 1978. Biochim. Biophys. Acta. 512:436-451) was calculated to be 1.4. In symmetrical 100 mM K+ solutions, the coupling ratio was decreased significantly (n = 0.9), indicating that the permeation process through states with increased ion occupancy became significant. We presented a diagrammatic representation linking the water-ion coupling ratio to the mode of ion permeation and suggested that the coupling ratio of one may represent the least hydrated ion flux in the single-file pore.

Cell Membrane Permeability↗

PubMed2003

Interaction between tetraethylammonium and permeant cations at the inactivation gate of the HERG potassium channel.

The fast inactivation of the human ether-à-go-go related gene product (HERG) channel is a form of C-type inactivation and is decelerated by external tetraethylammonium (TEA) and potassium. From the time constant of inactivation, the dissociation constants of TEA (K(TEA)) and potassium (K(K)) to the inactivation-impeding site were evaluated. K(TEA) was found to exhibit unexpected voltage dependence: K(TEA) decreased with depolarization. This was opposite the voltage dependence of K(K) on inactivation, in which permeating potassium impeded closure of the inactivation gate upon binding to a site in the pore (a "foot-in-the-door" mechanism). Further experiments on inactivation revealed anomalous mole fraction effects between permeating alkali cations and TEA, while no anomalous effects were seen between permeating ion species (K+, Rb+, Cs+). The results indicate that TEA and permeating ions impede inactivation through binding to different but closely interacting sites. K(TEA) was influenced by permeating ions through their bindings in the pore. As the size of the occupied ion was increased the dissociation constant of TEA to the ion-occupied pore decreased. Thus, we conclude that an ion bound to the inactivation-impeding site in the selectivity filter is located in close proximity to TEA bound at the entrance of the filter. The order of affinity of alkali cations for the inactivation-impeding site, Rb+ > Cs+ > K+, indicated that the selectivity of the site differed significantly from permeation selectivity, K+ > Rb+ > Cs+.

Animals↗

PubMed2003

[Clinico-statistical analysis of renal cell carcinomas in patients on hemodialysis].

Eleven patients on hemodialysis that were surgically treated for renal cell carcinomas during the recent 10 years at our institutes were clinically analyzed. Patients' ages at presentation ranged from 35 to 70 years with an average of 54.8 years. Nine of the 11 patients were males and 2 were females. Periods between the introduction of hemodialysis and the presentation ranged from 1 to 21 years with an average of 11.7 years. The most frequent cause of hemodialysis was chronic glomerulonephritis. Five patients presented with macroscopic hematuria, which was the most frequent clinical manifestation. Transperitoneal nephrectomy through a lumbar oblique incision was performed in 9 of 12 surgical procedures. Transperitoneal resection and retroperitoneal endoscopic resection were performed on 2 patients and 1 patient, respectively. Blood transfusion was performed on 2 patients with retroperitoneal hemorrhage before or after operation and 2 patients with pre-existing renal anemia. Pathologically, 9 patients had pT1a disease. Patients were followed up for up to 7 years and 11 months. One patient died of the disease and 2 patients died of unknown causes. In conclusion, surgical removal of renal cell carcinomas was well tolerated, safe and effective treatment in patients under hemodialysis.

Adult↗

PubMed2002

Thymidine phosphorylase and dihydropyrimidine dehydrogenase in bladder cancer.

Thymidine phosphorylase (TP) and dihydropyrimidine dehydrogenase (DPD) levels in transitional cell carcinoma of the bladder resected from 38 patients were examined by ELISA. TP levels in high-grade and invasive cancer were significantly higher than those in low-grade and superficial cancer, respectively. No significant differences in the DPD levels were observed among grades and stages, but the DPD/TP ratio was significantly lower in grade 3 tumor than in grade 1. These results demonstrated that 5'-deoxy-5-fluorouridine seemed to be useful for managing patients with grade 3 cancer. The present study also suggested that we might be able to exclude cases of bladder cancer in which 5-fluorouracil group medicines would be inappropriate candidates in treatment options by measuring both TP and DPD levels in the tumor.

Aged↗

PubMed2002

[A case of leiomyosarcoma of the spermatic cord].

A 44-year-old male was referred to our hospital for further treatment of lung and adrenal metastases from leiomyosarcoma occurring in the left spermatic cord. He had undergone high orchiectomy 5 months before, but no adjuvant therapy was done. Although systemic CYVADIC therapy (cyclophosphamide, vincristine, doxorubicin hydrochloride, dacarbazine) was performed in our hospital, he died of metastatic disease 10 months after the initial therapy. Leiomyosarcoma arising in the spermatic cord is a rare entity. We present a case of leiomyosarcoma of the spermatic cord, and to our knowledge, this is the 23rd case reported in Japan.

Adrenal Gland Neoplasms↗

PubMedDate not supplied

Computer-based sorting-to-matching in identity matching for young children with developmental disabilities.

We evaluated a computer-based sorting-to-matching procedure to teach matching-to-sample skills to seven young children with developmental disabilities who had failed to demonstrate identity matching-to-sample under the typical training procedure (such as observing a sample then selecting a comparison stimulus). In the sorting-to-matching procedure, rather than clicking on a comparison stimulus, the children moved the sample stimulus under the identical comparison stimulus. For all the children, identity matching-to-sample accuracy rapidly increased when the sorting-to-matching procedure was introduced, while it remained at chance levels in the typical training procedure. One of seven children showed collateral gains in accuracy with the typical training procedure after the exposure to the sorting-to-matching procedure.

Child↗