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Biomedical subjects

H Kasai

Publications and source records attributed to H Kasai.

At least 235 records · Page 13Linked to original sources
PubMed1993

Repair of 8-hydroxyguanine in DNA by mammalian N-methylpurine-DNA glycosylase.

8-Hydroxyguanine is one of the major base lesions implicated in mutagenesis induced by ionizing radiation and radiomimetic agents. This lesion appears to be repaired by human cells via multiple pathways including the one that involves a base glycosylase. Mouse N-methylpurine-DNA glycosylase, responsible for the removal of N-alkylpurines in DNA that are induced by simple monofunctional alkylating agents, also releases 8-hydroxyguanine from DNA in vitro and in vivo in Escherichia coli. The human N-methylpurine-DNA glycosylase, with a lower preference for N-alkylguanine than the mouse protein, removes the oxidized base less efficiently than the mouse protein. The recombinant mammalian glycosylases can rescue E. coli lacking MutM (Fpg) protein, the DNA glycosylase that is primarily responsible for removing 8-hydroxyguanine from the bacterial DNA.

Animals↗
PubMed1993

Evidence for two DNA repair enzymes for 8-hydroxyguanine (7,8-dihydro-8-oxoguanine) in human cells.

Two DNA repair enzymes for 8-hydroxyguanine (also known as 7,8-dihydro-8-oxoguanine; OH8Gua, oxo8Gua) have been identified in human HeLa cell nuclear extract. One is OH8Gua-glycosylase and the other is OH8Gua-endonuclease that lacks OH8Gua-glycosylase activity. They were separated by heparin-Sepharose column chromatography and characterized by endonuclease nicking assay or by measuring the OH8Gua released from substrate DNA using high pressure liquid chromatography-electrochemical detection. Both OH8Gua repair enzymes act only on the OH8Gua-containing strand of the duplex substrate DNA containing OH8Gua/C, OH8Gua/T, or OH8Gua/G. DNA containing OH8Gua/A base pair was very poor substrate for either enzymes. OH8Gua-endonuclease simultaneously cleaves phosphodiester bonds on both sides of the OH8Gua residue, leaving 5'-hydroxy and 3'-hydroxy groups.

Base Sequence↗
PubMed1993

Subcellular distribution of Ca2+ release channels underlying Ca2+ waves and oscillations in exocrine pancreas.

Agonists trigger Ca2+ waves and oscillations in exocrine gland cells. Our confocal Ca2+ imaging revealed three distinct phases during the Ca2+ waves in the rat pancreatic acinar cell. Rises in Ca2+ concentration were initiated at a small trigger zone, or T zone, in the granular area; then, Ca2+ waves rapidly spread within the area and, at high agonist concentrations, propagated slowly toward the basal pole. Injection of inositol 1,4,5-trisphosphate (IP3) or Ca2+ from patch pipettes demonstrated the presence of high sensitivity IP3 receptors at the T zone, Ca(2+)-induced Ca2+ release channels in the granular area, and low sensitivity IP3 receptors in the basal area. The IP3 receptors at the T zone appeared to generate autonomous Ca2+ spikes and to initiate patterned Ca2+ oscillations. Thus, heterogeneous cytosolic localization of Ca2+ release channels plays a key role in Ca2+ waves and oscillations.

Acetylcholine↗
PubMed1993

Agonist-induced localized Ca2+ spikes directly triggering exocytotic secretion in exocrine pancreas.

We investigated how agonist-induced patterned rises in cytosolic Ca2+ concentration ([Ca2+]i) regulate exocytotic secretion in the rat pancreatic acinar cell. The distribution of [Ca2+]i was visualized with a confocal microscope, which revealed that a Ca2+ ionophore, A23187, induced slow and homogeneous [Ca2+]i rises, while acetylcholine (ACh) always triggered primary Ca2+ spikes at the granular area which bears secretory granules. Secretion was monitored by measuring capacitance with the patch clamp method. Errors in the estimates of membrane capacitance (C) due to changes in conductance (G) were experimentally as well as theoretically evaluated to be one-tenth of the actual signals. We found that A23187 raised G without changing C at a low concentration, while it triggered asynchronous rises in G and C with lags in C, at a high concentration. By contrast, ACh triggered simultaneous rapid rises in G and C. Our results support the hypothesis that exocytotic secretion is less sensitive to Ca2+ than to ion channels and is directly caused by agonist-induced primary Ca2+ spikes at the granular area. It is therefore suggested that spatio-temporal patterns of Ca2+ oscillations could play a key role in exocytotic secretion from the exocrine acinar cell.

Acetylcholine↗
PubMed1993

Quantitative analysis of 8-hydroxyguanine in peripheral blood cells: an application for asbestosis patients.

The quantitative analysis of 8-hydroxy-2'-deoxyguanosine (oh8dG) in human peripheral blood cells was carried out to find integrated biomarkers for estimating cancer risk. The change of the oh8dG levels over time in two healthy volunteers was measured to evaluate a intraindividual variance and each individual value was confirmed to be almost constant when they maintained usual life style. We applied this measurement to asbestosis patients who had worked in dockyard for 19-42 years. The oh8dG were detected in all samples and ranged from 0.77 to 1.28/10(5) deoxyguanosine (dG)8. No significant differences was observed in mean values of oh8dG between patients (1.00 +/- 0.17/10(5)dG) and hospital control group without asbestos exposure (1.03 +/- 0.20/10(5)dG) No association was found with the status of cigarette smoking. The oh8dG level in peripheral blood cells is therefore not a sensitive biomarker for past asbestos exposure at low levels.

Aged↗
PubMed1993

Cytosolic Ca2+ gradients, Ca2+ binding proteins and synaptic plasticity.

Trains of spikes encoded by presynaptic neurons are decoded into rises in cytosolic Ca2+ concentration both in presynaptic terminals and in postsynaptic dendrites. Intracellular [Ca2+] rises trigger neurotransmitter release and also induce short- and long-term modifications of synaptic efficacy. These modifications can be potentiation or depression depending on the intensity of stimuli. A dynamic mechanism, "dynamic decoding", is proposed to understand the multiplicity of the functions of Ca2+, based on recent knowledge of Ca2+ binding proteins and of the dynamics of Ca2+ signaling. The dynamic model is in many ways superior to static models, and may be applied to various neuronal functions including the induction of long-term plasticity in cerebral cortex.

Animals↗
PubMed1993

Induction of mutations in mouse FM3A cells by treatment with riboflavin plus visible light and its possible relation with formation of 8-hydroxyguanine (7,8-dihydro-8-oxoguanine) in DNA.

Photosensitized formation of 8-hydroxyguanine (oh8Gua; 7,8-dihydro-8-oxoguanine, oxo8Gua) in cellular DNA and its repair was examined in mouse FM3A cells. oh8Gua was generated 7-fold above the background level by 10 min irradiation with visible light in the presence of riboflavin (160 microM0 and repaired to 60-70% of initial level after 2 h post-incubation. By this treatment, mutation frequency that was measured by counting ouabain-resistant colonies, was increased 7-fold above the background frequency. The accumulation of unrepaired oh8Gua in DNA generated by treatment with riboflavin plus visible light correlates to induction of mutations. Thus, oh8Gua will contribute to the mutation induced by visible light as well as spontaneous mutations.

Animals↗
PubMed1993

Elevated level of 8-hydroxydeoxyguanosine in DNA of liver, kidneys, and brain of Long-Evans Cinnamon rats.

Long-Evans Cinnamon (LEC) rats, a mutant strain originating from Long-Evans rats, spontaneously develop hereditary hepatitis followed by hepatocellular carcinoma. The hepatic disorder in LEC rats is associated with their abnormal copper metabolism; metal-catalyzed reactions often give rise to oxygen radicals, which may be related to the carcinogenesis. By means of high-pressure liquid chromatography with electrochemical detection, cellular DNA damage caused by oxygen radicals can be assessed in terms of the amount of 8-hydroxydeoxyguanosine (oh8dG). We assayed the amount of oh8dG in DNA of liver, kidneys, and brain of LEC and Long-Evans Agouti (LEA) control rats in seven groups (n = 3 to 6) aged from 5 weeks to 24 months. Control rats, a healthy sibling line, were age-matched. The amount of oh8dG was correlated with the severity of the age-related clinical symptoms in LEC rats. The amount was higher in LEC rats than in the controls, especially in the liver at the acute stage of hepatitis. These findings suggest that oxygen radicals may be important in the carcinogenesis that occurs in LEC rats.

8-Hydroxy-2'-Deoxyguanosine↗
PubMed1993

Vasorelaxant mechanism of KRN2391 and nicorandil in porcine coronary arteries of different sizes.

1. The relaxant mechanisms of action of KRN2391, a novel vasodilator, and nicorandil on epimyocardial coronary artery (2.5- 3.0 mm outer diameter) and mid-myocardial coronary artery (0.8-1.0 mm outer diameter) were investigated in porcine isolated coronary arteries. In addition, the vasorelaxant responses of KRN2391 and nicorandil were compared with those of nitroglycerin and cromakalim, a K+ channel opener, in epi- and mid-myocardial coronary arteries. 2. Nitroglycerin showed a more potent relaxant effect on epi-myocardial coronary arteries than on mid-myocardial coronary arteries, whereas cromakalim produced greater relaxation responses in mid-myocardial coronary arteries. There was no difference between epi- and mid-myocardial coronary arteries in terms of the relaxant effect of KRN2391 and nicorandil. 3. Relaxation induced by KRN2391 in epi- and mid-myocardial coronary arteries was inhibited by oxyhaemoglobin, a pharmacological antagonist of nitrovasodilators, and glibenclamide, a pharmacological antagonist of K+ channel opening drugs. However, the inhibitory effect of glibenclamide on KRN2391-induced relaxation was greater in mid-myocardial coronary artery than in epi-myocardial coronary artery. 4. Relaxation induced by nicorandil was inhibited by oxyhaemoglobin alone in epi-myocardial coronary arteries and by both oxyhaemoglobin and glibenclamide in mid-myocardial coronary arteries. 5. In epi- and mid-myocardial coronary arteries, relaxation induced by cromakalim was inhibited by glibenclamide but not by oxyhaemoglobin, whereas relaxation induced by nitroglycerin was inhibited by oxyhaemoglobin but not by glibenclamide. 6. These results suggest that KRN2391 and nicorandil exhibit a dual mechanism of action acting partly as a nitrate and partly as a K+ channel opener. The mechanism of action of these drugs depend on the segment of coronary artery studied. Furthermore, the dual mechanism of action of KRN2391 and nicorandil seems to contribute to the equipotent relaxant effect between epi- and mid-myocardial coronary arteries.

Animals↗
PubMed1993

Dissimilarity in the mechanisms of action of KRN2391, nicorandil and cromakalim in canine renal artery.

In the present study, we examined the mode of action of KRN2391 (N-cyano-N'-(2-nitroxyethyl)-3-pyridinecarboximidamide monomethanesulphonate) in isolated canine renal artery compared with those of nicorandil and cromakalim. KRN2391 (10(-8)-3 x 10(-5) M), nicorandil (10(-7)-3 x 10(-4) M) and cromakalim (10(-8)-3 x 10(-5) M) relaxed renal arteries contracted by 25 mM KCl in a concentration-dependent manner. KRN2391-induced relaxation was inhibited by methylene blue (10(-5) M) and glibenclamide (10(-6) M). Nicorandil-induced relaxation was inhibited by methylene blue, but not by glibenclamide. The concentration-relaxation curve for cromakalim displayed a rightward parallel shift in the presence of glibenclamide. In the control observation, KRN2391 and nicorandil also produced full relaxation, but cromakalim did not. The present results suggest that KRN2391 acts as both a nitrate and a potassium channel opener, and nicorandil acts only as a nitrate and only in canine renal artery.

Animals↗
PubMed1993

Comparison of the effects of KRN2391 and other coronary dilators on porcine isolated coronary arteries of different sizes.

The present study was performed to determine whether KRN2391 (N-cyano-N'-(2-nitroxyethyl)-3-pyridinecarboximidamide monomethanesulphonate), a novel vasodilator, shows different effects on porcine isolated coronary arteries of different sizes. The vasodilating effects of KRN2391 on porcine large (2.5-3.0 mm outer diam.) and small (0.8-1.0 mm) coronary arteries were also compared with those of cromakalim, nicorandil, nifedipine, nitroglycerin and adenosine. The relaxant effects of these drugs were examined in coronary arteries contracted by 25 mM KCl. Nitroglycerin caused greater relaxation in large vessels than in small vessels. In contrast, adenosine, nifedipine and cromakalim caused greater relaxation in small vessels. However, there was no difference between large and small vessels in the relaxing effects of KRN2391 and nicorandil. These unique features of KRN2391 and nicorandil appear to be beneficial in ischaemic heart disease.

Adenosine↗
PubMed1993

Inotropic effects of staurosporine, NA 0345 and H-7, protein kinase C inhibitors, on rabbit ventricular myocardium: selective inhibition of the positive inotropic effect mediated by alpha 1-adrenoceptors.

The influence of protein kinase C (PKC) inhibitors, staurosporine, NA 0345 and H-7, on the alpha 1- and beta-adrenoceptor-mediated positive inotropic effect (PIE) was studied in rabbit ventricular myocardium. Staurosporine (1-10 nM), NA 0345 (10-100 nM) and H-7 (1-10 microM) selectively attenuated the PIE mediated by alpha 1-adrenoceptors at concentrations that did not affect the beta-mediated PIE and basal force of contraction. Staurosporine at higher concentrations (> 10 nM) decreased the basal force, while NA 0345 and H-7 did not. In membrane fractions derived from rabbit ventricular muscle, neither staurosporine, NA 0345 nor H-7 modified the specific [3H]prazosin binding at the concentrations that elicited the functional modulation. Accumulation of [3H]inositol monophosphate (IP1) induced by alpha 1-adrenoceptor stimulation was not affected by the PKC inhibitors. Phorbol 12,13-dibutyrate (PDBu), a PKC activator, also selectively attenuated the alpha 1-mediated PIE, but in association with the inhibition of the alpha 1-mediated IP1 accumulation. Staurosporine (1 nM), but not H-7, antagonized the PDBu-induced inhibitory action on the alpha 1-mediated PIE. These findings indicate that staurosporine, NA 0345 and H-7 produce a selective inhibition of the alpha 1-mediated PIE, probably through inhibition of the alpha 1-adrenoceptor-mediated activation of PKC. On the contrary, externally administered phorbol ester may act by uncoupling of alpha 1-adrenoceptors to activation of phospholipase C through a pathway different from endogenous diacylglycerol to lead to a selective inhibition of the alpha 1-mediated PIE.

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗
PubMed1993

[Detection of chromosomal numerical aberration in glioma by FISH (fluorescence in situ hybridization)].

FISH method with chromosome specific DNA probe to interphase nuclei has been useful for the analysis of chromosomal numerical aberration in human brain tumor. We applied the FISH method to 9 gliomas and one glioma cell line (KMU-100) with 4 kinds of chromosomes of number 7, 9, 10 and 17. The predominant specific aberration in glioma were revealed the increased signal numbers of chromosome 7&17 and the decreased signal numbers of chromosome 9&10. The inactivation of tumor suppressor genes and the activation of oncogenes have been suggested as the principal mechanism of tumorigenesis in human cancer. The definite oncogenes have not still been identified on chromosome 7&17 and tumor suppressor genes on chromosome 9&10. We discussed the mechanism of tumorigenesis with one or more oncogenes on chromosome 7&17 and of one or more tumor suppressor genes on chromosome 9&10 in glioma.

Adult↗