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K Yamagami

Publications and source records attributed to K Yamagami.

At least 19 recordsLinked to original sources
PubMed1992

The effects of aging on muscarinic receptor/G-protein coupling in the rat hippocampus and striatum.

In the striatum and hippocampus, there is a loss of sensitivity to muscarinic agonists with age which has been traced to events early in the signal transduction pathway. Our laboratory has therefore focussed on investigations at this level. The current experiments investigate the effects of age on G-protein/receptor interactions by using competitive binding assays to measure the ability of GppNHp to decrease the proportion of receptors bound to G-proteins in the absence and the presence of added Mg2+. L-[3H]Quinuclidinyl benzilate was used as a nonselective ligand and [3H]pirenzepine as an M1 selective ligand. We find that: (1) muscarinic receptors and G-proteins in the striatum appear to become loosely coupled with age, with no change in Mg2+ sensitivity. (2) M1-receptor/G-protein complexes in the hippocampus display increased sensitivity to the presence of Mg2+ with age, with those from old but not young tissue requiring added Mg2+ in order to uncouple. This effect, however, may not be M1 specific.

Aging↗
PubMed1992

Decrement of muscarinic receptor-stimulated low-KM GTPase in striatum and hippocampus from the aged rat.

Previous studies have shown that there is an age-related loss of responsiveness in several different receptor systems (e.g. beta-adrenergic, dopaminergic and muscarinic). Our research, using perifused striatal slices and examining muscarinic agonist enhancement of K(+)-evoked dopamine release, has determined that at least part of the loss of sensitivity in muscarinic receptors (mAChR) may occur early in the post-receptor signal transduction process. The present study was carried out to further characterize and localize this deficit by examining carbachol- and oxotremorine-stimulated low-KM guanosine triphosphatase (GTPase) activity in striatal as well as hippocampal tissue obtained from adult (6 months) and old (24 months) Wistar rats. Receptor stimulated low-KM GTPase catalyzes the conversion of GTP to GDP to end the signal transduction cycle and is an indicator of receptor-G-protein coupling/uncoupling. The results showed that stimulated GTPase activity was significantly reduced in hippocampal and striatal tissue from the old animals. These findings suggest that there may be an age-related coupling/uncoupling deficit between muscarinic receptor and G-proteins, and that this deficit may contribute to the reduced mAChR responsiveness in senescence.

Aging↗
PubMed1992

Possible role of surface potential in the gating mechanism of Ca2+ channels in cat adrenal chromaffin cells: studies with fura-2 microfluorometry.

The cytosolic free Ca2+ concentration ([Ca]in) in isolated cat chromaffin cells was measured by fura-2 microfluorometry. During 30 mM KCl depolarization or sucrose substitution for NaCl, a reduction in external Ca2+ concentration under optimal conditions paradoxically caused a rise in [Ca]in and, in separate experiments, in catecholamine secretion. The results support a previously suggested role of surface potentials in the gating mechanism of Ca2+ channels.

Adrenal Medulla↗
PubMed1992

A muscarinic receptor agonist mobilizes Ca2+ from caffeine and inositol-1,4,5-trisphosphate-sensitive Ca2+ stores in cat adrenal chromaffin cells.

To gain some understanding of the characteristics of intracellular Ca2+ stores of cat adrenal chromaffin cells, we investigated the effects of ryanodine, a blocker of Ca(2+)-induced Ca2+ release channels in muscle, on both cytosolic Ca2+ concentration and catecholamine secretion induced by caffeine or methacholine. The results suggest that Ca2+ stores consist of at least two compartments, one which is sensitive to both caffeine and inositol-1,4,5-trisphosphate (IP3), and the other which is sensitive to IP3 alone.

Adrenal Glands↗
PubMed1992

Isolation of cDNAs for LCE and HCE, two constituent proteases of the hatching enzyme of Oryzias latipes, and concurrent expression of their mRNAs during development.

The hatching enzyme of medaka consists of two types of proteases (HCE, LCE). cDNA clones for LCE and HCE were isolated from a lambda gt11 cDNA library constructed with poly(A)+ RNA of Day 3 embryos. LCE cDNA is 936 bp long and contains an 813-bp open reading frame encoding a preproenzyme with a 20-amino-acid signal sequence, a 51-amino-acid propeptide, and a 200-amino-acid mature enzyme. For HCE, two distinct cDNAs (HCE21, HCE23) having nucleotide sequences with 92.8% similarity were obtained. These cDNAs contain open reading frames encoding preproenzymes of 279 and 270 amino acids, respectively. The mature enzyme forms of both consist of 200 amino acids, the similarity between them being 95.5%. On Northern blotting analysis, the transcripts of LCE and HCE genes were first detected coincidentally in Day 2 embryos shortly before the production of LCE and HCE, accumulated thereafter in parallel, and dramatically decreased after hatching. The amino acid sequence, the HExxH motif, which is known to constitute an active site in some Zn proteases, is also found in LCE and HCE. However, the sequence analyses strongly suggest that both the enzymes belong to the astacin (protease) family, being distinct from sea urchin hatching enzyme, which is reportedly similar to collagenase.

Amino Acid Sequence↗
PubMed1992

Two constituent proteases of a teleostean hatching enzyme: concurrent syntheses and packaging in the same secretory granules in discrete arrangement.

Formation, accumulation, and storage of two components of the Oryzias latipes hatching enzyme, high and low choriolytic enzymes (HCE and LCE), were examined by immunocytochemical and immunoblotting methods. Both of the enzymes were found to be formed specifically in the hatching gland cells at the stages of lens formation to eye pigmentation and their accumulation proceeded markedly and concurrently up to Day 5.5 embryos (the stage just before hatching). The amount of HCE formed was more abundant than that of LCE. In the hatching gland cells, HCE and LCE were found to be packaged in the same secretory granules but in distinct arrangement; HCE is localized to the inside of granules whereas LCE is situated at the periphery of the same granules. Their segregated arrangement is compatible with their relative quantities formed per embryo. The results provide not only the cellular and developmental basis for a view that this hatching enzyme is an enzyme system composed of HCE and LCE but also a clue to the regulatory mechanism of concurrent syntheses of two different specific proteins in the same embryonic cell.

Animals↗
PubMed1992

Possible regulation of caffeine-induced intracellular Ca2+ mobilization by intracellular free Na+.

To gain some understanding of the regulatory mechanism involved in caffeine-induced Ca2+ release in adrenal chromaffin cells, we took advantage of the paradoxical observation that removal of divalent cations potentiated the secretory response to caffeine. We measured the concentration of cytosolic free Ca2+ ([Ca]in) in isolated cat chromaffin cells, by fura-2 microfluorometry, to see whether there was any correlation between the secretory response and the rise in [Ca]in. The caffeine-induced [Ca]in rise and catecholamine secretion were increased by treatment of cells with a divalent cation-deficient solution. These potentiated responses were strongly inhibited either by pretreatment with ryanodine, by the reduction of the external Na+ concentration, or by the addition of Ca2+ channel blockers. Removal of divalent cations caused a large rise in the cytosolic free Na+ concentration ([Na]in), which was measured using SBFI microfluorometry. This rise in [Na]in was reduced either by adding Ca2+ channel blockers or by reducing the external Na+ concentration. These results show a good correlation between caffeine-induced Ca2+ release and [Na]in at the time of stimulation, suggesting that caffeine-induced Ca2+ release is regulated by [Na]in.

Animals↗
PubMed1992

[The influence of paraquat on cell cycle--analysis of cell kinetics using DNA/BrdU staining].

We examined the in vitro and in vivo effects of paraquat on the cell cycle. After we exposed paraquat to the cultured cell (MDCK), we examined cell kinetics by flow cytometry with BrdU-PI double staining. And we administered paraquat intravenously to the rats, we collected and separated rat's liver and pulmonary cells, and we examined the cell kinetics by same method. Consequently our study found that the cells in the S-phase were noted to be abundant, and we suggested that paraquat apparently arrested the cell cycle at S time, and that DNA damage was importance in the mechanism of paraquat toxicity.

Animals↗
PubMed1992

[Hatching enzyme].

Explore the source record for details and available documents.

Amino Acid Sequence↗
PubMed1991

Antitumor activity of 2'-deoxy-2'-methylidenecytidine, a new 2'-deoxycytidine derivative.

The antitumor activity of 2'-deoxy-2'-methylidenecytidine (DMDC), an inhibitor of DNA synthesis, was examined and compared with that of 1-beta-D-arabinofuranosylcytosine (ara-C) against various murine tumors and human tumor xenografts. Against P388 murine leukemia, repeated treatments of DMDC were more effective than its single administration. Interestingly, DMDC was effective against colon 26 murine carcinoma, M5076 murine reticulum cell sarcoma, LX-1 human lung cancer xenograft, and SK-Mel-28 human melanoma xenograft, which are less sensitive or refractory to ara-C, while DMDC was not more potent against murine leukemias P388 and L1210 than ara-C. The in vitro cytotoxic effects of DMDC and ara-C against L1210 leukemia cells were prevented dose dependently by deoxycytidine, suggesting that DMDC, like ara-C, may require phosphorylation by deoxycytidine kinase for antitumor activity. DMDC was effective against human and murine experimental tumor models, especially nonleukemic tumors refractory to ara-C, suggesting that DMDC will be a promising agent for the treatment of cancer.

Animals↗
PubMed1991

GABA inhibits the rise in cytosolic free calcium concentration in depolarized immature cerebellar Purkinje cells.

gamma-Aminobutyric acid (GABA) reduced the peak rise or slowed the rate of rise in cytosolic free calcium concentration ([Ca]in) induced by quisqualate, kainate, or high KCl in immature cerebellar Purkinje cell bodies. The sustained rise or repeated transient of [Ca]in induced by tetraethylammonium, veratridine, or Bay-K-8644 was lowered to the basal level by adding GABA, although the inhibition by GABA of Bay-K-8644-induced rise in [Ca]in was only slight and transient in some cells. These findings indicate that GABA inhibits the rise in [Ca]in by hyperpolarizing the membrane potentials at Purkinje cell bodies.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗
PubMed1991

Internal Ca2+ mobilization by muscarinic stimulation increases secretion from adrenal chromaffin cells only in the presence of Ca2+ influx.

The cytosolic free Ca2+ concentration ([Ca2+]in) in single cat and bovine adrenal chromaffin cells was measured to determine whether or not there was any correlation between the [Ca2+]in and the catecholamine (CA) secretion caused by muscarinic receptor stimulation. In cat chromaffin cells, methacholine (MCh), a muscarinic agonist, raised [Ca2+]in by activating both Ca2+ influx and intracellular Ca2+ mobilization with an accompanying CA secretion. In bovine cells, MCh elevated [Ca2+]in by mobilizing intracellular Ca2+ but did not cause CA secretion. The MCh-induced rise in [Ca2+]in in cat cells was much higher than that in bovine cells, but when Ca2+ influx was blocked, the rise was reduced, with a concomitant loss of secretion, to a level comparable to that in bovine cells. Intracellular Ca2+ mobilization due to muscarinic stimulation substantially increased secretion from depolarized bovine and cat cells, where a [Ca2+]in elevated above basal values was maintained by a continuous Ca2+ influx. These results show that Ca2+ released from internal stores is not effective in triggering secretion unless Ca2+ continues to enter across the plasma membrane, a conclusion suggesting that secretion depends on [Ca2+]in in a particular region of the cell.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗
PubMed1991

Correlations between IL-2 enhancing activity and clinical parameters in patients with rheumatoid arthritis and systemic lupus erythematosus.

In a previous paper (Tomura, K. et al. Tohoku J. Exp. Med., 1989, 159, 171-183), we discovered IL-2 enhancing factor(s) designated B cell derived-growth enhancing factor-2 (BGEF-2), which enhanced IL-2 dependent cell proliferation, and reported that BGEF-2 was produced by B cells of the patients with rheumatoid arthritis (RA) and systemic lupus erythematosus (SLE) only when they were in the active stage of the disease. In this paper, we studied relationship between each IL-2 enhancing activity from B cell supernatant of the patients with these diseases and clinical parameters. IL-2 enhancing activities did not correlate with erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP), but correlated with plasma concentrations of gamma-globulin from the patients with RA and SLE in the active stages. IL-2 enhancing activities correlated with hypocomplementemia and leukocytopenia in the patients with SLE, and also correlated with RAHA titer in the patients with RA. Moreover, on several patients with RA or SLE in the active stages, diminution of IL-2 enhancing activity was found when they were in the remission stage after treatments. These findings suggested that IL-2 enhancing activity (i.e., BGEF-2 activity) correlated with activity of these diseases and supported the hypothesis that BGEF-2 played an important role in the polyclonal B cell activation and autoantibody production in patients with these diseases.

Adult↗
PubMed1990

Tetraethylammonium stimulates adrenomedullary secretion by causing fluctuations in a cytosolic free Ca concentration.

Tetraethylammonium (TEA) caused marked fluctuations in a cytosolic free Ca concentration, which was measured by fura-2 microfluorimetry in bovine adrenal chromaffin cells. At the same time. TEA stimulated catecholamine secretion from cat and bovine chromaffin cells. Present results suggest that TEA indirectly increases the Ca2+ influx by depolarizing the cell membrane and consequently stimulates catecholamine secretion.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗
PubMed1979

Ca2+ binding sites in plasma membranes of rat liver and hepatoma cells, and effect of concanavalin A on the Ca2+ binding sites and cellular uptake of Ca2+.

1. Plasma membranes isolated from rat livers and ascites hepatoma cells (AH-130, AH-7974) were assayed for specific Ca2+ binding sites using 45Ca2+ and a Millipore filtration technique. The presence of higher (Kd = 1.4--1.5 . 10(-5) M) and lower (Kd = 0.9--1.0 . 10(-4) M) affinity sites in both liver and hepatoma membranes was observed. The hepatoma plasma membranes however, showed 1.4--2.1-fold as many Ca2+ binding sites (higher and lower affinity sites) as the liver plasma membranes on the basis of protein. 2. Concanavalin A stimulated the specific Ca2+ binding to liver and hepatoma plasma membranes, showing a maximal stimulation (3--5-fold) at 100 microgram/ml. Succinyl concanavalin A was less effective, whereas wheat germ agglutinin and ricinus lectin were ineffective. 3. Concanavalin A stimulated the Ca2+ uptake by AH-7974 cells. The concanavalin A-mediated stimulation of Ca2+ uptake showed lectin-concentrations and Ca2+-concentration dependencies similar to those in the concanavalin A-mediated stimulation of Ca2+ binding.

Animals↗