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D Okada

Publications and source records attributed to D Okada.

35 records · Page 2Linked to original sources
PubMed1996

Differential effects of protein kinase C on neuronal nitric oxide synthase activity in rat cerebellar slices and in vitro.

The effects on neuronal nitric oxide synthase (NOS) of protein kinase C (PKC) activation in rat cerebellar slices and of in vitro phosphorylation by PKC were compared. Incubation of slices with 1-aminocyclopentane-1,3-trans-dicarboxylic acid (trans-ACPD) or phorbol myristate acetate (PMA) in the presence of okadaic acid (OA) shifted the calcium sensitivity of neuronal NOS in the homogenate or in the cytosolic fraction. trans-ACPD promoted translocation of PKC activity to the particulate fraction in the slices. PMA in the presence of OA enhanced phosphorylation of GAP43 protein in the slices. These results ensured that both treatments activated PKC in the slice. However, when neuronal NOS in the slice treated with PMA and OA, in which GAP43 phosphorylation was detected, was immunoprecipitated by a specific antibody, no indication of neuronal NOS phosphorylation was obtained. Nevertheless, PKC phosphorylated partially purified neuronal NOS in vitro. Phosphorylated neuronal NOS showed greater activity than unphosphorylated NOS, but their calcium sensitivity was identical. These data indicated that neuronal NOS is not susceptible to PKC-dependent phosphorylation in cerebellar slices and that the calcium-sensitivity shift of neuronal NOS takes place without direct phosphorylation of neuronal NOS, suggesting the involvement of unknown proteins whose phosphorylation would regulate the calcium sensitivity of neuronal NOS in the cerebellum.

Animals↗
PubMed1995

Protein kinase C modulates calcium sensitivity of nitric oxide synthase in cerebellar slices.

The possible modulation of nitric oxide (NO) synthase (NOS) activity by protein kinase C (PKC) was investigated. Incubation of rat cerebellar slices with the specific metabotropic glutamate receptor agonist, (+/-)-1-aminocyclopentane-trans-1,3-dicarboxylate (trans-ACPD) increased cyclic GMP concentration two-fold. The increase was dose-dependently blocked by the protein kinase inhibitors staurosporine and calphostin C. Phorbol 12-myristate 13-acetate (PMA), a PKC activator, increased cyclic GMP concentration without glutamate receptor activation. The cyclic GMP increases induced by PMA and trans-ACPD were independent of extracellular calcium blocked by N omega-nitro-L-arginine, a specific NOS inhibitor, and were not additive. Measurement of citrulline formation in cerebellar slices confirmed that NOS was activated by trans-ACPD and the activation was blocked by calphostin C. These results suggest that metabotropic glutamate receptor activates NOS through PKC. The calcium dependency of NOS activation was assessed in slices incubated with PMA and okadaic acid. NOS in both PMA-treated and untreated slices had similar activities at 100 nM free calcium, whereas at 25-70 nM free calcium, NOS in PMA-treated slices was more active than that in untreated slices. These results suggest that PKC regulates NO release in resting neurons by modulating the sensitivity of NOS at low calcium concentrations.

Amino Acid Oxidoreductases↗
PubMed1992

Cerebellar long-term potentiation under suppressed postsynaptic Ca2+ activity.

To study the roles of postsynaptic Ca2+ activity in cerebellar synaptic plasticity, we used a patch-recording technique in Purkinje cell dendrites. While the combination of parallel fibre stimulation and 8-bromo cyclic guanosine monophosphate (Br-cGMP) application produced long-term depression (LTD) of the parallel fibre/Purkinje cell transmission, the same stimuli evoked long-term potentiation (LTP) during postsynaptic injection of Ethyleneglycol-bis-(beta-amino-ethylether)-N, N, N', N'-tetraacetate (EGTA). Furthermore, in the presence of alpha-aminobutyric acid (GABA), parallel fibre stimulation plus Br-cGMP produced LTP of extracellular K+ increases following parallel fibre stimulation. These results suggest that postsynaptic Ca2+ activity in Purkinje cells is negatively correlated to the direction of plastic changes and that the Ca2+ changes and cGMP play distinct roles in cerebellar synaptic plasticity.

Animals↗
PubMed1992

Two pathways of cyclic GMP production through glutamate receptor-mediated nitric oxide synthesis.

The selective agonists for the metabotropic glutamate receptor and the ionotropic non-N-methyl-D-aspartate (NMDA) glutamate receptor, (+/-)-1-aminocyclopentane-trans-1,3-dicarboxylic acid (ACPD) and (R,S)-alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate (AMPA), respectively, increased the cyclic GMP (cGMP) content in cerebellar slices prepared from adult rats. The ACPD-induced rise in cGMP level was blocked by compounds known to antagonize metabotropic glutamate receptors, such as DL-2-amino-3-phosphonopropionic acid and L-2-amino-4-phosphonobutyric acid, but not by ionotropic glutamate receptor antagonists, D-2-amino-5-phosphonovaleric acid and 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), whereas the AMPA-induced rise in cGMP level was suppressed by CNQX. Both rises in cGMP level involved nitric oxide synthase (NOS), because NG-methyl-L-arginine (NMLA), an inhibitor of NOS, blocked both cGMP level rises, and excess L-arginine reversed the effect of NMLA. After lithium chloride treatment, which could exhaust phosphatidylinositol phosphates, ACPD no longer increased cGMP levels, whereas AMPA was still effective. In a calcium-free medium, ACPD still induced a rise in cGMP level, whereas AMPA did not. When the molecular layer was isolated to determine the cGMP content separately from that in the rest of the cerebellar cortex, it was found that ACPD raised the cGMP level mainly in the molecular layer, whereas AMPA raised it in both sections.(ABSTRACT TRUNCATED AT 250 WORDS)

1-Methyl-3-isobutylxanthine↗
PubMed1991

Endogenous nitric oxide release required for long-term synaptic depression in the cerebellum.

Conjunctive stimulation of climbing and parallel fibres in the cerebellum evokes a long-term depression of parallel-fibre Purkinje-cell transmission, a phenomenon implicated as the cellular mechanism for cerebellar motor learning. It is suspected that the increase in cyclic GMP concentration that occurs after activation of climbing fibres is required to evoke long-term depression. Excitatory amino acids are known to cause the release of nitric oxide (NO), resulting in elevation of the cGMP level in the cerebellum. Here we report that endogenous NO is released after stimulation of climbing fibres, that long-term depression evoked by conjunctive stimulation of parallel and climbing fibres is blocked by haemoglobin (which strongly binds NO) or L-NG-monomethyl-arginine (an inhibitor of NO synthase), and that exogenous NO or cGMP can substitute for the stimulation of climbing fibres to cause long-term depression in rat cerebellar slices. These results demonstrate that the release of endogenous NO is essential for the induction of synaptic plasticity in the cerebellum.

6-Cyano-7-nitroquinoxaline-2,3-dione↗
PubMed1990

Long-term synaptic changes in rat cerebellar slices reflected in extracellular K+ activity.

In rat cerebellar slices, a [K+]o increase evoked locally by molecular layer stimulation was recorded by a K(+)-sensitive microelectrode. This K+ response was reduced clearly during application of low-Ca2+ medium, kynurenate or 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX). Sustained depression of the K+ response by about 20% was observed after simultaneously but not after alternately combined stimulation of the molecular layer and the white matter/granule cell layer. It is concluded from these results that long-term depression of parallel fiber-Purkinje cell transmission can be detected as depression of the K+ response.

Adaptation, Physiological↗
PubMed1990

Peri-operative immunotherapy with OK-432.

Pre- and postoperative intradermal administration of OK-432 enhanced the SU-PS skin reaction in patients with gastric cancer, but failed to prevent a fall in the NK activity induced by the operation. The change in NK activity was not associated with a change in the proportion of Leu 7-positive cells, but was related to Leu 11a-positive cells. Intradermal injection of OK-432 increased the proportion of Leu 7-positive cells in the patients in whom they accounted for less than 20% of lymphocyte population. The case was the same with Leu 11a-positive cells. Intravenous injection of OK-432 tended to increase suppressor-inducer T cells (CD4+2HA+ cells), B cells and Leu 7-positive cells. Particularly, the proportions of OK-M1-positive cells and MHC class II antigen-positive cells increased in all patients. Immunotherapy with OK-432 given intravenously at a dose of 0.1 KE appeared to be safe because no side effects were essentially observed.

Combined Modality Therapy↗
PubMed1989

Differential effects of phospholipase inhibitors in long-term potentiation in the rat hippocampal mossy fiber synapses and Schaffer/commissural synapses.

Bath application of the inhibitors of phospholipases, nordihydroguaiaretic acid (NDGA) and p-bromo-phenacyl bromide (BPB), to the rat hippocampal slices suppressed long-term potentiation (LTP) in Schaffer/commissural-CA1 pyramidal synapses. On the other hand, neither of the two inhibitors suppressed LTP in mossy fiber-CA3 pyramidal cell synapses. BPB did not suppress phosphatidylinositol-specific phospholipase C (PI-PLC) activity of the slices. These results suggested that the mechanisms of LTP were quite different in the CA1 and CA3 subfields of rat hippocampus: in CA1, the involvement of an arachidonate metabolism was strongly suggested, whereas in CA3, an arachidonic acid cascade may not be necessary for LTP.

Acetophenones↗
PubMed1989

Transducin activation by molecular species of rhodopsin other than metarhodopsin II.

Decay of metarhodopsin II was accelerated by hydroxylamine treatment or dark incubation of metarhodopsin II at 30 degrees C. The products thus obtained after decay of metarhodopsin II induced GTPase activity on transducin as well as metarhodopsin II suggesting that rhodopsin could activate transducin after the decay of metarhodopsin II intermediate. After urea-treated bovine rod outer segment membrane was completely bleached, rhodopsin in the membrane was regenerated by the addition of 11-cis retinal at various temperatures between 0 and 37 degrees C. The capacity to induce GTPase activity on transducin and phosphate incorporating capacity catalyzed by rhodopsin kinase were measured on such rhodopsins. The results showed that: (1) Regeneration of alpha band of rhodopsin was complete regardless of regeneration temperature; (2) When regenerated at temperatures below 10 degrees C, rhodopsins induced a GTPase activity on transducin in the dark even after treatment with hydroxylamine, whereas rhodopsins after regeneration at temperatures above 13 degrees C did not; (3) When regenerated at 0 degrees C, rhodopsin was phosphorylated if incubated with rhodopsin kinase and ATP in the dark, whereas the spectrally regenerated rhodopsin at 30 degrees C was not. The complete quenching of functions of photoactivated rhodopsin was achieved by recombination with 11-cis retinal at temperatures above 13 degrees C but not below 10 degrees C suggesting the existence of a low temperature intermediate upon regeneration.

Animals↗
PubMed1989

[A significance of dual parameter flow cytometric DNA analysis using the anti-keratin antibody].

Flow cytometric DNA analysis using the anti-cytokeratin antibody was carried out in order to estimate more reliable measurement in single cell suspension obtained from solid tumors. It was difficult to detect a DNA aneuploidy with DI of 2.0 by one parameter analysis of DNA. Whereas it could be detected easily by using dual parameter analysis of cytokeratin and DNA. And also, the pattern of DNA multiploidy could be selected for cytokeratin positive cell population by gate analysis.

Antibodies↗
PubMed1989

[Study of fluorescence in situ hybridization for detection of chromosome aberration].

The authors applied fluorescence in situ hybridization (FISH) technique for the detection of chromosome aberration in interphase nuclei using the probe specific to alphoid repeats on chromosome 11 and X. Chromosome 11 specific probe showed two major spots in lymphocyte nuclei, while X specific probe showed single spot in male and double spots in female respectively. On the other hand three spots were detected in most of the nuclei from HeLa cells with 11 and X specific probes. We concluded that FISH with the use of chromosome specific probe may become a useful and reliable tool for the detection of chromosome aberration in interphase nuclei.

Cell Nucleus↗
PubMed1988

Pertussis toxin suppresses long-term potentiation of hippocampal mossy fiber synapses.

The long-term potentiation (LTP) was studied using rat hippocampal slices in vitro. LTP in mossy fiber-CA3 pyramidal cell synapses was markedly suppressed in slices prepared from rats which had previously received intraventricular injection of pertussis toxin (PTX), compared with the bovine serum albumin-injected controls, suggesting the involvement of G-proteins in the mechanism of LTP in mossy fiber synapses. In contrast, LTP in Schaffer/commissural-CA1 pyramidal synapses was not affected by PTX pretreatment.

Action Potentials↗
PubMed1988

Purification method of bovine rhodopsin kinase using regeneration of rhodopsin.

We report a rapid and high-yield purification method of bovine retinal rhodopsin kinase. According to our method, 500 micrograms of rhodopsin kinase was purified from 100 bovine retinae within 12 h. Rhodopsin kinase bound to bleached rhodopsin was extracted effectively from rod outer segment membranes after regeneration of rhodopsin by the incubation with exogenous 11-cis-retinal. Subsequent DE52 column chromatography further purified the protein to homogeneity on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The purified rhodopsin kinase had an apparent molecular weight of 68,000 and phosphorylated rhodopsin at the rate of 10 nmol phosphate/min/mg of the enzyme.

Animals↗