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Biomedical subjects

T Baba

Publications and source records attributed to T Baba.

At least 37 records · Page 2Linked to original sources
PubMed1994

Sustained left ventricular tachycardia terminated by dipyridamole: cyclic AMP-mediated triggered activity as a possible mechanism.

Sustained VT in two patients was terminated by intravenous administration of dipyridamole, an adenosine transport inhibitor. VT was induced by rapid atrial or ventricular pacing, isoproterenol, or dibutyryl cyclic AMP infusion, or exercise. VT also was aborted by adenosine triphosphate or acetylcholine injection, or by vagal stimulation. VT was terminated or prevented by verapamil or propranolol. In addition, arrhythmias were prevented by oral administration of dipyridamole. These results suggest that VT is due to cyclic AMP-mediated triggered activity and that inhibition by dipyridamole may be due to a reduction in the intracellular concentration of cyclic AMP.

Acetylcholine↗
PubMed1994

The link between insulin resistance and hypertension. Effects of antihypertensive and antihyperlipidaemic drugs on insulin sensitivity.

Insulin resistance is generally interpreted as the physiological state under which insulin causes a reduced glucose-lowering effect. Hyperinsulinaemia is considered to be a result of insulin resistance. Many recent studies have suggested that hyperinsulinaemia and/or insulin resistance is associated with an elevated blood pressure, whereas several other studies have found a modest or no association. Many factors (e.g. adiposity, age, ethnic difference) have been suggested to confound the insulin-blood pressure relationship. Insulin is thought to raise blood pressure by a few possible mechanisms (e.g. stimulating sympathetic nervous system activity, enhancing renal tubular sodium reabsorption). On the other hand, insulin has also been reported to possess a vasodilatory property. Neither an insulin infusion within a physiological range nor continuously sustained hyperinsulinaemia in patients with insulinoma are associated with elevated blood pressure. Therefore, the relationship between insulin and blood pressure is still under discussion. Among the antihypertensive drugs, angiotensin converting enzyme (ACE) inhibitors seem to have marginal effects of improving insulin sensitivity, but whether this effect would lead to a better prognosis for diabetic patients remains to be proven. Lipid lowering drugs appear to show no benefit in lowering blood glucose.

Animals↗
PubMed1994

Gene expression of erythropoietin in hepatocellular carcinoma.

A 68-year-old man with hepatocellular carcinoma complicated by erythrocytosis showed an increased plasma level of immunoreactive erythropoietin (EPO). Northern blot analysis and RT-PCR (reverse transcriptase and polymerase chain reaction) of EPO mRNA extracted from a surgical specimen indicated high expression of EPO mRNA in the tumor tissue. Histological and immunocytochemical examination showed that the tumor was a hepatocellular carcinoma with predominant immunostaining for EPO. The erythrocytosis improved and the high serum EPO level decreased after resection of the tumor. This is the first demonstration of EPO mRNA expression in hepatocellular carcinoma tissue by RT-PCR.

Aged↗
PubMed1994

[Effects of ileal perfusion of carbohydrates on upper GI motility and pancreatic exocrine secretion].

The aim of this study was to determine if upper gut function and pancreatic exocrine secretion are affected by the presence of unabsorbed carbohydrate in the distal ileum. In this investigation, starch or glucose was perfused into the canine ileum. This study showed that ileal perfusion of both starch and glucose delayed gastric emptying and prolonged small bowel transit time. Furthermore, glucose had greater effects on gastrointestinal transit time than starch. In contrast, amylase output was increased by ileal perfusion of starch, but was not affected by that of glucose. Our results suggest that the ileal regulation of gastrointestinal transit and amylase output could be mediated by different mechanisms.

Amylases↗
PubMed1994

Expression of branching enzyme II of maize endosperm in Escherichia coli.

A cDNA clone encoding maize branching enzyme II (BEII) has been independently isolated from a maize endosperm cDNA library. The deduced protein sequence of maize BEII was compared with that of BE from diverse sources. The gene encoding mature BEII of maize endosperm has been expressed in E. coli using the T7 promoter. The expressed BEII was purified to near homogeneity so that amylolytic activity and bacterial BE could be completely eliminated from the BE preparation. The expressed enzyme showed very similar properties to those of BEII purified from developing maize endosperm. This result confirmed our earlier report that BEII had a lower rate of branching amylose and the rate of branching amylopectin was twice that of branching amylose. This study also showed a greater advantage of purifying BEII from the bacterial expression system than from developing maize endosperm. Most importantly, this study has established a useful tool to study the structure-function relationships of the maize BE using site-directed mutagenesis.

1,4-alpha-Glucan Branching Enzyme↗
PubMed1993

Antigenic protein specific for C3H strain mouse is a mitochondrial stress-70 protein.

Cells derived from C3H strain mouse produce an antigenic protein (CSA) specific for this strain [Kusakabe, M., et al. (1988) J. Cell Biol. 107, 257-265]. To examine the molecular basis of CSA, cDNA cloning of the antigenic protein was carried out. The deduced amino acid sequence demonstrates that CSA is the same protein as peptide-binding protein 74 (PBP74), a novel member of the stress-70 family. However, comparison of the PBP74/CSA sequences between C3H/HeN and BALB/c strain mice reveals the substitution of two amino acids in the substrate-recognition domain of the stress-70 protein. Western blot analysis indicates that one out of these two residues, arginine at residue 578 in the PBP74/CSA sequence of C3H mouse, contributes to the immunogenicity of CSA. Moreover, the subcellular localization of PBP74/CSA in mitochondria is also demonstrated by immunohistochemical analysis using anti-CSA monoclonal antibody. Thus, it is interesting that a genetic marker sequence in mice is located on the gene encoding a mitochondrial stress-70 protein.

Amino Acid Sequence↗
PubMed1993

Identification, cDNA cloning, and gene expression of soluble starch synthase in rice (Oryza sativa L.) immature seeds.

Three forms of soluble starch synthase were resolved by anion-exchange chromatography of soluble extracts from immature rice (Oryza sativa L.) seeds, and each of these forms was further purified by affinity chromatograph. The 55-, 57-, and 57-kD proteins in the three preparations were identified as candidates for soluble starch synthase by western blot analysis using an antiserum against rice granule-bound starch synthase. It is interesting that the amino-terminal amino acid sequence was identical among the three proteins, except that the 55-kD protein lacked eight amino acids at the amino terminus. Thus, these three proteins are products of the same gene. The cDNA clones coding for this protein have been isolated from an immature rice seed library in lambda gt11 using synthetic oligonucleotides as probes. The deduced amino acid sequence of this protein contains a lysine-X-glycine-glycine consensus sequence for the ADP-glucose-binding site of starch and glycogen synthases. Therefore, we conclude that this protein corresponds to a form of soluble starch synthase in immature rice seeds. The precursor of the enzyme contains 626 amino acids, including a 113-residue transit peptide at the amino terminus. The mature form of soluble starch synthase shares a significant but low sequence identity with rice granule-bound starch synthase and Escherichia coli glycogen synthase. However, several regions, including the substrate-binding site, are highly conserved among these three enzymes. Blot hybridization analysis demonstrates that the gene encoding soluble starch synthase is a single-copy gene in the rice genome and is expressed in both leaves and immature seeds. These results suggest that soluble and granule-bound starch synthases play distinct roles in starch biosynthesis of plant.

Amino Acid Sequence↗
PubMed1992

Calreticulin is present in the acrosome of spermatids of rat testis.

We have already succeeded in purifying a calcium-binding protein (CalBP) from rat spermatogenic cells [Nakamura et al., Biochem. Biophys. Res. Commun., 176 (1991) 1358]. In this study, the location of this protein within rat testis was examined, using a rabbit antisera for this protein. The antigen was localized on the developing acrosomes during spermiogenesis. The NH2-terminal amino acid sequence obtained for rat CalBP was identical to that of calreticulin obtained for the skeletal muscle of mice and closely resembled that for rabbit calreticulin. On the immunoblot analysis, the purified rat CalBP reacted with an antibody raised against rabbit skeletal muscle calreticulin. The results indicate that calreticulin is present in the acrosome of spermatids of rat testes.

Acrosome↗
PubMed1992

Identification of the fourth member of the mammalian endoprotease family homologous to the yeast Kex2 protease. Its testis-specific expression.

We used the polymerase chain reaction to identify a mouse testis cDNA that represented another member of a growing class of mammalian endoproteases involved in the processing of precursor proteins. This cDNA encoded a 655-residue protein, designated PC4, containing a bacterial subtilisin-like catalytic domain closely related to those of the recently characterized precursor-processing endoproteases, furin, PC1/PC3, PC2, and Kex2. Within this domain, the amino acid sequence of PC4 was 70, 58, 55, and 45% identical with those of mouse furin, mouse PC1/PC3, mouse PC2, and yeast Kex2, respectively. Northern blot analysis indicated that the PC4 mRNA was detectable only in the testes after the 20th day of postnatal development. Moreover, this message was mainly expressed in the round spermatids. These data suggest that PC4 represents a prime candidate for a precursor-processing endoprotease in the testicular germ cells and that its gene expression is regulated during spermatogenesis.

Amino Acid Sequence↗
PubMed1992

Response of microglial cells to experimental rat glioma.

The response of indigenous CNS microglia to an experimentally induced glioma has been studied in rat brain using lectin histochemistry with the Griffonia simplicifolia B4-isolectin. The study was undertaken 2 weeks after tumor cell injection when tumor size was near maximal. Reactive microglial cells formed a dense band that surrounded most of the well-circumscribed tumor mass, and extended along the corpus callosum into the contralateral cerebral hemisphere. From the periphery inward, reactive microglia extended into the tumor tissue, where large numbers of them were found to be present as microglia-derived macrophages. The lectin stain, which also labels endothelial cells, revealed a highly vascularized tumor with ongoing neovascularization apparent as vascular sprouts. Moderate numbers of lectin-stained blood monocytes were localized primarily inside the vessel lumina. Our results show that microglial cells react to brain tumors; however, it remains to be determined whether the microglial response represents an active antitumor defense mechanism that could be manipulated during immunotherapeutic approaches.

Animals↗
PubMed1992

Genetics of neurofibromatosis 1 in Japan: mutation rate and paternal age effect.

We have performed formal genetic studies on 26 patients (14 males, 12 females) with neurofibromatosis 1 (von Recklinghausen's disease, NF1) in Japan. Family studies of 74 members of 18 kindreds revealed that 50% of the cases were caused by a new mutation; the mutation rate was assumed to be 7.3-10.5 x 10(-5). A tendency of paternal age effect, which was not accounted for by the maternal age effect, was observed, but live-birth order had no significant effect. Genetic linkage of neurofibromatosis 1 to the NF1 gene or the genetic marker in the pericentric region of chromosome 17 was established in 3 informative families.

Age Factors↗
PubMed1992

Immunophenotypic analysis of infiltrating leukocytes and microglia in an experimental rat glioma.

The appearance and cellular distribution of major histocompatibility complex (MHC), as well as lymphocytic and macrophage antigens has been studied in a fully developed experimental rat forebrain glioma. Activated microglial cells and microglia-derived macrophages expressing CR3 complement receptor molecules and MHC class II (Ia) antigen were found throughout the tumor, and with increased density along the tumor's periphery. MHC class I antigen expression was entirely absent from tumor cells, and found only occasionally on microglia. The expression of leukocyte common antigen, and CD4 and CD8 antigens was conspicuous throughout the tumor, and associated with lymphocytes, perivascular cells, and microglia. Cells expressing the ED2 macrophage epitope were almost exclusively of the perivascular type and revealed a distribution dissimilar to that of cells positive for Ia antigen. The ED2 epitope was found sporadically on ramified microglial cells. The results show that despite heavy infiltration with blood mononuclear and CNS microglial cells, the tumor showed no evidence of destruction caused by inflammatory cells. Possible mechanisms of tumor immunosuppressive activity preventing the full immunological activation of microglia and blood mononuclear cells are discussed.

Animals↗