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Biomedical subjects

Y Sasaki

Publications and source records attributed to Y Sasaki.

At least 19 recordsLinked to original sources
PubMed1995

Novel deltorphin heptapeptide analogs with potent delta agonist, delta antagonist, or mixed mu antagonist/delta agonist properties.

A series of deltorphin (DLT: Tyr-D-Met-Phe-His-Leu-Met-Asp-NH2) analogs in which Leu5 and/or Met6 were mainly replaced by t-Leu(Tle) and/or N alpha-alkylated glycine were synthesized and examined for their receptor binding properties and in vitro bioactivities by guinea pig ileum (GPI) and mouse vas deferens (MVD) assays. [Tle5]DLT(2) showed a dramatic decrease in the MVD potency when compared to the parent peptide and was found to have a potent delta receptor antagonist activity against various delta agonists with Ke values of 16-311 nM. Interestingly, the antagonist potency of 2 against DPDPE as agonist was 20-fold weaker than that against deltorphins or Leu-enkephalin. Among the analogs in which Met6 was replaced by an N alpha-alkylated Gly residue, [N alpha-isobutyl-Gly6]DLT(5) behaved as a mixed mu antagonist/delta agonist while its isomeric analogs in which the N alpha-alkyl is n-butyl (4) or (R or S) sec-butyl (6a,b) were very potent delta receptor agonists. Analogs 2, 4, 6a, and 6b were highly stable against rat brain and rat plasma enzymes and thus may represent a starting point for the development of novel receptor-specific compounds useful as ligands for studies of opioid receptors.

Amino Acid Sequence↗
PubMed1995

The voltage-dependent K+ channel (Kv1.5) cloned from rabbit heart and facilitation of inactivation of the delayed rectifier current by the rat beta subunit.

We have isolated a cDNA coding for a delayed rectifier K+ channel (RBKV1.5) from rabbit heart. The amino acid sequence of RBKV1.5 displays a homology to that of other K+ channels of Kv1.5 class. Overall amino acid identity between RBKV1.5 channel and Kv1.5 channel of other species is about 85%. RNA blot analysis revealed the expression of the primary transcript in various rabbit tissues, at the highest level in both the atrium and ventricle. When expressed in Xenopus oocytes, RBKV1.5 current showed a delayed rectifier type characteristics, which was converted to rapidly inactivating currents upon coexpression with a beta subunit.

Amino Acid Sequence↗
PubMed1995

Purification of an ATP-dependent actin-binding protein from a lower eukaryote, Physarum polycephalum.

A novel protein with a molecular mass of 55 kDa, as determined by SDS-PAGE, was purified from plasmodia of Physarum polycephalum. The protein bound to actin filaments with a stoichiometry of 0.27 moles per mole of actin with an apparent dissociation constant of 4 x 10(-8) M. In the presence of ATP, the protein dissociated from actin filaments. Adenosine 5-(gamma-thio)triphosphate and adenyl-5'-yl imidodiphosphate also abolished the actin-binding activity of the protein, but GTP did not. Because the cytoplasmic concentration of ATP oscillates in association with the shuttle streaming of the cytoplasm, it is possible that this protein might be involved in the actin-linked regulation of cytoplasmic streaming.

Actins↗
PubMed1995

Location of light-repressible, small GTP-binding protein of the YPT/rab family in the growing zone of etiolated pea stems.

YPT/rab proteins are ras-like small GTP-binding proteins that serve as key regulators of vesicular transport. The mRNA levels of two YPT/rab genes in pea plants are repressed by light, with the process mediated by phytochrome. Here, we examined the mRNA expression and the location of the two proteins, pra2- and pra3-encoded proteins, using monoclonal antibodies. The pra2 and pra3 mRNA levels were highest in the stems of dark-grown seedlings. The corresponding proteins were found in the cytosol and the membranes of the stems. Most of the pra2 protein was in the growing internodes, especially in the growing region, but the pra3 protein was widespread. These results suggest that the pra2 protein is important for vesicular transport in stems, possibly contributing to stem growth in the dark, and that the pra3 protein is important for general vesicular transport. The amounts of pra2 and pra3 proteins decreased with illumination. The decrease in these proteins may be related to the phytochrome-dependent inhibition of stem growth that occurs in etiolated pea seedlings.

Animals↗
PubMed1995

Expression and phosphorylation of rat c-met/hepatocyte growth factor receptor during rat liver regeneration.

Hepatocyte growth factor receptor is identified as a heterodimeric tyrosine kinase encoded by the c-met gene. This study was designed to determine how the c-met/hepatocyte growth factor receptor participates in the intracellular events involved in rat liver regeneration induced by administration of carbon tetrachloride. Expression of the rat c-met mRNA increased, peaking 24 h after carbon tetrachloride administration almost in parallel with MET protein expression. Histochemical studies demonstrated that expression of the rat c-met was enhanced in cells surrounding the damaged areas, and also that the distribution of cells expressing MET was almost in accordance with that of cells expressing proliferating cells nuclear antigen. The MET protein underwent intense tyrosine phosphorylation peaking at 12 h after carbon tetrachloride administration, and prior to DNA synthesis. Phospholipase C gamma and phosphatidylinositol 3-kinase, intracellular signal transducing molecules containing Src homology 2 domain, were associated with the MET protein following tyrosine phosphorylation in vivo. These observations suggest that expression and tyrosine phosphorylation of MET protein associated with signal transducing molecules may provide a mechanism whereby hepatocyte growth factor exerts its action on hepatocyte growth during rat liver regeneration induced by carbon tetrachloride administration.

Animals↗
PubMed1995

Opioid mu- and kappa-receptor mediate phospholipase C activation through Gi1 in Xenopus oocytes.

In the Xenopus oocytes expressing mu- or kappa-opioid receptors, agonist-induced currents were observed only when the oocyte was coinjected with Gi1 alpha RNA and pretreated with K-252a, a potent inhibitor of protein kinases. The evoked currents were abolished by intracellular injection of EGTA or inositol 1,4,5-trisphosphate and the current-voltage relationship revealed that they are mediated through typical calcium-dependent chloride channels. These findings suggest that the mu- and kappa-receptors mediate phospholipase C activation through Gi1 alpha, and that these receptor mechanisms including downstream signalings might be inhibited by phosphorylation in vivo in the Xenopus oocyte.

Animals↗
PubMed1995

Magnetic resonance imaging of osteomyelitis in the mandible. Comparative study with other radiologic modalities.

Magnetic resonance imaging of 14 histopathologically confirmed cases of osteomyelitis of the mandible was retrospectively reviewed. The findings of magnetic resonance imaging were compared with conventional radiography, computed tomography, bone scintigraphy, and histopathologic examinations. All lesions in bone marrow were shown as areas of low (64%) or low-to-intermediate (36%) signal intensity on T1-weighted images, and areas of high (29%), mixed (high and low, 21%; high and intermediate, 36%) or low (14%) signal intensity on T2-weighted images. Histopathologically, high T2-weighted signal intensity areas that showed enhancement after contrast injection corresponded to active infection. These were not collections of pus but were predominantly areas of granulation tissue. Magnetic resonance imaging showed larger areas of abnormality than plain radiography or computed tomography. Bone scintigraphy did not accurately reveal the locations of lesions but showed heterogeneous increased uptake in all patients. MRI was an extremely useful technique for assessing osteomyelitis of the mandible.

Acute Disease↗
PubMed1995

Identification of virulence-associated antigens and plasmids in Rhodococcus equi from patients with AIDS.

Rhodococcus equi is an emerging opportunistic pathogen of human immunodeficiency virus-infected patients. However, little is known about the characteristics of R. equi isolates from humans. This study characterized the plasmid content, expression of a virulence-associated antigen, and mouse virulence of 19 R. equi isolates from patients with and without AIDS. EcoRI digestion patterns and Southern, Western, and virulence analyses of these isolates with cryptic plasmids allowed definition of a new category of R. equi. Isolates from patients with AIDS tended either to be virulent and have 15- to 17-kDa antigens and an 85-kb plasmid (10(6) bacteria needed for lethality) or have intermediate virulence (10(7) bacteria needed for lethality) and one of four distinct large plasmids that share DNA homology and express a 20-kDa antigen. Most of the non-AIDS isolates were avirulent (> 10(8) bacteria needed for lethality) and did not express any of these antigens.

AIDS-Related Opportunistic Infections↗
PubMed1995

Effect of ethanol on p36 protein kinase substrate and insulin receptor substrate 1 expression and tyrosyl phosphorylation in human hepatocellular carcinoma cells.

Ethanol inhibits insulin (IN) and epidermal growth factor (EGF)-induced hepatocyte DNA synthesis. Growth factor receptor kinases, such as IN and EGF, phosphorylate insulin receptor substrate (IRS-1) and p36 protein kinase substrate, respectively, on tyrosine residues. IRS-1 and p36 are thought to be important intracellular signal transduction molecules involved in the regulation of cell growth. These investigations explored the effect of ethanol additions on the expression and tyrosyl phosphorylation (TP) of p36 and IRS-1 in a human hepatocellular carcinoma cell line (FOCUS) in relationship to cell proliferation induced by IN and serum growth factor stimulation. It was found that p36 was constitutively and highly expressed in serum-starved cells and protein, and mRNA levels did not change with cell proliferation induced by growth factors. However, exposure of FOCUS cells to ethanol additions substantially inhibited TP of p36. The early TP of IRS-1 induced by IN stimulation was also reduced by ethanol additions. Finally, there was a parallel decrease of FOCUS cell proliferation in ethanol-exposed cultures. These studies suggest that one possible mechanism of ethanol inhibitory effect on cell proliferation is through reduced TP of putative intracellular signal transduction molecules, such as p36 and IRS-1.

Annexin A2↗
PubMed1995

Endocardial fragmented electrogram and prediction of ventricular tachycardia by body surface signal-averaged electrocardiographic mapping.

Signal-averaged (SA) electrocardiography and SA electrocardiographic mapping were performed in 50 patients with old myocardial infarction, 19 of whom had left ventricular aneurysm and 11 of whom had clinical sustained ventricular tachycardia. The SA electrocardiogram and SA electrocardiographic mapping data were then compared with those obtained by endocardial catheter mapping in patients with or without fragmented electrograms, sustained ventricular tachycardia, and ventricular aneurysm. Compared to SA electrocardiography, the SA map correlates with sustained VT with improved sensitivity but decreased specificity. However, SA electrocardiographic mapping had the advantage of displaying the extent of the body surface area that was positive for late potentials. In addition, the site of the longest endocardial fragmented electrogram could be predicted by SA electrocardiographic mapping, suggesting that this technique deserves wider clinical application.

Action Potentials↗
PubMed1995

Pathogenesis of Rhodococcus equi infection in mice: roles of virulence plasmids and granulomagenic activity of bacteria.

Virulence of Rhocococcus equi ATCC 33701 and its plasmid-cured derivative ATCC 33701P- was compared in BALB/c and C3H/HeJ mice in terms of bacterial growth kinetics and histological changes in the liver, spleen and lungs, and humoral immune responses. Injection with a sublethal dose of 10(6) ATCC 33701 in mice resulted in microabscess formation after rapid multiplication in the liver and spleen by day 4, and then the bacteria were gradually eliminated with the formation of granuloma and the production of specific antibodies against 15- to 17-kDa antigens of the virulent bacteria. By contrast, ATCC 33701P- was avirulent as shown by early elimination of viable bacteria and no evidence of net multiplication in the organs. Histopathological changes consisted of only slight, transient infiltration of neutrophils and macrophages in the liver. Although live ATCC 33701P- did not evoke any humoral or histological responses in the mice, a large inoculum (10(8)) of killed ATCC 33701 and ATCC 33701P- resulted in the formation of granuloma in the liver and accelerated extramedullary hemopoiesis in the spleen. These results suggest that the pathogenesis of R. equi infection involves at least two important virulence determinants, both of which play critical roles in the disease: one is the virulence plasmid, which is required for R. equi to resist and grow within host cells; and the other is the granulomagenic activity that is related to the lipids and nature of the cell wall of the species, which induces the characteristic pathological changes.

Actinomycetales Infections↗
PubMed1995

[Detection of Mycoplasma pneumoniae from throat swab by polymerase chain reaction].

Polymerase chain reaction (PCR) with primers directed against the 16S-rRNA gene of Mycoplasma pneumoniae was used to diagnose M. pneumoniae infections, and the results were compared with those of culture and serology methods. Eighty (22%) of 363 throat swab samples from patients with acute respiratory complaints gave positive results by using the PCR method. Sixty-seven (18.5%) of the samples were positive in culture method. Of 35 samples which were unreliable culture results due to contamination with other bacteria, 13 gave positive results in the PCR method. Of the 97 cases obtained throat swabs and paired sera, 28 (28.9%) showed positive results by the PCR assay, and 29 (29.9%) by serology method (particle agglutination test). The positive rate was increased to 36% by using both the PCR and the serology methods. From these results it was concluded that the PCR method is useful for laboratory diagnosis of M. pneumoniae infections.

Base Sequence↗
PubMed1995

In vitro influence of Mycoplasma penetrans on activation of peripheral T lymphocytes from healthy donors or human immunodeficiency virus-infected individuals.

Mycoplasma penetrans is a mycoplasma species newly isolated from the urine of human immunodeficiency virus (HIV)-infected individuals and presents the only case in which an association has been found between antibodies against a mycoplasma and HIV infection. To further explore the effects of M. penetrans on the immune system, we studied the influence of this mycoplasma on peripheral blood mononuclear cells (PBMCs) from healthy donors and HIV-infected individuals. M. penetrans induced, in addition to blastogenesis of PBMCs, a significant proliferative response associated with the expression of some activation markers such as CD69, HLA-DR, and CD25. This M. penetrans-dependent lymphocyte activation was observed not only in healthy donors but also in HIV-infected persons at different stages of the disease. In addition, our study revealed that both CD4+ and CD8+ T lymphocytes were responsive to M. penetrans. Interestingly, the mitogenic activity of M. penetrans was associated with mycoplasma cells but not with the supernatants of mycoplasma culture. The potent stimulating activity of M. penetrans on T lymphocytes from HIV-infected individuals is of particular interest in view of the supposed contribution of immune activation to HIV replication and disease progression.

Antigens, CD↗
PubMed1995

Identification of virulent Rhodococcus equi by amplification of gene coding for 15- to 17-kilodalton antigens.

During a survey of the prevalence of virulent Rhodococcus equi at horse-breeding farms by plasmid and protein profiles, cryptic plasmids of various sizes were found in 66 (3.8%) of 1,725 isolates from feces of horses and 129 (5.9%) of 2,200 isolates from soil. Twenty-two isolates, which contained cryptic plasmids of different sizes, were found by plasmid profiles, and their protein profiles and mouse pathogenicities were examined. Of the 22 isolates, 7 were virulent R. equi, contained both virulence and cryptic plasmids, and expressed 15- to 17-kDa antigens. The remaining 15 isolates were avirulent and did not express the antigens: 6 strains contained cryptic plasmids of two different sizes and 9 strains contained cryptic plasmids of various sizes. A PCR assay was developed for the rapid identification of virulence plasmids of R. equi. Oligonucleotide primers, derived from the sequence of a gene coding for the 15- to 17-kDa virulence-associated antigens of R. equi, amplified a 564-bp product from all the tested isolates harboring a virulence plasmid. This PCR product hybridized with virulence plasmid DNA in the Southern hybridization assay. Virulence plasmid-cured derivatives and all of the tested isolates harboring cryptic plasmids only were negative. The PCR is a rapid, sensitive, and specific test for the identification of virulent R. equi from environmental isolates compared with standard techniques, such as plasmid and protein profiles and the mouse pathogenicity test, and is considered to be a useful tool for epidemiological studies.

Animals↗
PubMed1995

The time course of myosin light-chain phosphorylation in blood-induced vasospasm.

The phosphorylation of an M(r) 20,000 myosin light chain (MLC20) promotes the generation of contractile force through actin-myosin adenosine triphosphatase in most agonist-mediated vascular smooth muscle cell contraction. However, the role of calcium-mediated contractile processes in sustained arterial narrowing after subarachnoid hemorrhage remains unknown. In a femoral artery model of vasospasm, whole blood was applied to arteries in 54 rats for periods of 2 to 10 days; the contralateral artery treated with platelet-rich plasma served as matched control. During the early stage of vasospasm (Days 2-5), in the media of arteries exposed to blood, MLC20 phosphorylation (including diphosphorylated forms) increased significantly (30-38%; P < 0.05); total medial MLC20 during this interval was comparable to that in controls. After 5 days, however, total MLC20 decreased markedly (> 90%; P < 0.01) compared with controls; phosphorylated MLC20 was undetectable during this interval. MLC20-mediated contractile processes may be prominent in the early stages of arterial narrowing after subarachnoid hemorrhage; later stages are associated with the loss of MLC20 and the possible persistence of arterial narrowing by other mechanisms.

Animals↗
PubMed1995

Synthesis and opioid activities of [D-Leu-8]Dynorphin(1-8) analogs containing a reduced peptide bond, psi(CH2-NH).

[D-Leu8]Dynorphin(1--8)-NH2 analogs, in which each peptide bond was systematically replaced with a psi(CH2NH) peptide bond, were synthesized by the solid-phase method. The psi(CH2NH) bond was introduced by the Boc-amino acid aldehyde/NaCNBH3 method on a solid support. In the syntheses of the analogs, undesirable double alkylation took place at the sequences of Tyr1 psi(CH2NH)Gly2 and Gly2 psi(CH2NH)Gly3, possibly due to the low steric hindrance of the glycine residue. To suppress the double alkylation, a minimum amount of aldehydes was employed. In the receptor binding assay, the psi(CH2NH) replacement of N-terminal peptide bonds which led to 1 psi 2-(2) and 2 psi 3-analogs (3) resulted in a marked reduction in binding affinities for mu-, delta-, and kappa-opioid receptors, while that of the other peptide bonds afforded analogs with a high kappa-receptor affinity. A 3 psi 4-analogs (4) showed extremely high kappa-receptor selectivity (mu/kappa Ki ratio = 339, delta/kappa Ki ratio = 24104). In the in vitro bioactivity assay (guinea pig ileum assay), 2 showed a very low IC50 ratio (2.0) in the presence and absence of peptidase inhibitors whereas those of other analogs were >27, suggesting that the introduction of the CH2NH isostere at Tyr1-Gly2 greatly enhanced the enzymatic stability of the parent peptide. Furthermore, analogs 2 and 3 showed a very low sensitivity to the inhibitory effect of NaCl plus 5'-guanylylimidodiphosphate on their binding at a kappa-receptor site as compared with the other analogs and the parent peptide. These results suggest that the two analogs (2 and 3) have partial kappa-antagonist properties.

Amino Acid Sequence↗