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T Yada

Publications and source records attributed to T Yada.

At least 73 records · Page 4Linked to original sources
PubMed1998

A regional gradient of cardiac intrinsic rhythmicity depicted in embryonic cultured multiple hearts.

We used optical methods to examine the spatial gradient of intrinsic rhythmicity in early-stage multiple-heart chick embryos. The latter were induced experimentally in whole-embryo culture. The embryos were cut microsurgically through the tissue of the anterior intestinal portal at the 5- to early 7-somite developmental stage. Spontaneous electrical activity in 4 to 6 segmented hearts, during the 7- to 10-somite stages of development, were monitored simultaneously by means of multiple-site optical recordings of membrane potential activity, using a voltage-sensitive merocyanine-rhodanine dye (NK2761). Each segment of the heart exhibited its own inherent rhythmicity. In quadruple hearts, the order of the rhythmicity was often left-caudal segment>right-caudal segment>left-cephalic segment>right-cephalic segment; the heart rate in the left-caudal segment was often faster than that in the other segments. An atypical pattern of "bursting" rhythm was observed in the cephalic segments suggesting that, in these segments, the development of rhythmicity is relatively poor. These findings strongly emphasize the concept that, in the early phases of cardiogenesis, the formation of a regional gradient of pacemaker activity (i.e. a spatial gradient of intrinsic rhythmicity) results in the functional self-organization of the pacemaking area.

Action Potentials↗
PubMed1998

Automatic extraction of motifs represented in the hidden Markov model from a number of DNA sequences.

MOTIVATION: Automatic extraction of motifs that occur frequently on a set of unaligned DNA sequences is useful for predicting the binding sites of unknown transcription factors. Several programs for this purpose have been released. However, in our opinion, they are not practical enough to be applied to a large number of upstream sequences. RESULTS: We propose a new program called YEBIS (Yet another Environment for the analysis of BIopolymer Sequences) which is capable of extracting a set of motifs, without any a priori knowledge, from a number of functionally related DNA sequences. Using the hidden Markov model, these motifs are represented in a more general form than other conventional methods, such as the weight matrix method. When applied to several sets of benchmark data, it was found that YEBIS had comparable capability to the existing methods, but was much faster. Moreover, it could extract all known motifs from the LTR sequences (long terminal repeat sequences) in a single run. Finally, it could be successfully applied to approximately 400 human promoter sequences and some of the extracted motifs turned out to be known cis-elements. Therefore, YEBIS could be a practical tool for exploring the upstream sequences of genomic ORFs, some of which are regulated in a similar fashion. AVAILABILITY: YEBIS will be distributed to academic users free of charge. All requests should be sent to the address below. CONTACT: E-MAIL: yada@tokyo.jst.go.jp

Algorithms↗
PubMed1998

[Ca2+]i-reducing action of cAMP in rat pancreatic beta-cells: involvement of thapsigargin-sensitive stores.

In the present study, we examined the ability of adenosine 3',5'-cyclic monophosphate (cAMP) to reduce elevated levels of cytosolic Ca2+ concentration ([Ca2+]i) in pancreatic beta-cells. [Ca2+]i and reduced pyridine nucleotide, NAD(P)H, were measured in rat single beta-cells by fura 2 and autofluorescence microfluorometry. Sustained [Ca2+]i elevation, induced by high KCl (25 mM) at a basal glucose concentration (2.8 mM), was substantially reduced by cAMP-increasing agents, dibutyryl cAMP (DBcAMP, 5 mM), an adenylyl cyclase activator forskolin (10 microM), and an incretin glucagon-like peptide-1-(7-36) amide (10(-9) M), as well as by glucose (16.7 mM). The [Ca2+]i-reducing effects of cAMP were greater at elevated glucose (8.3-16.7 mM) than a basal glucose (2.8 mM). An inhibitor of protein kinase A (PKA), H-89, counteracted [Ca2+]i-reducing effects of cAMP but not those of glucose. Okadaic acid, a phosphatase inhibitor, at 10-100 nM also reduced sustained [Ca2+]i elevation in a concentration-dependent manner. Glucose, but not DBcAMP, increased NAD(P)H in beta-cells. [Ca2+]i-reducing effects of cAMP were inhibited by 0.3 microM thapsigargin, an inhibitor of the endoplasmic reticulum (ER) Ca2+ pump. In contrast, [Ca2+]i-reducing effects of cAMP were not altered by ryanodine, an ER Ca(2+)-release inhibitor, Na(+)-free conditions, or diazoxide, an ATP-sensitive K+ channel opener. In conclusion, the cAMP-PKA pathway reduces [Ca2+]i elevation by sequestering Ca2+ in thapsigargin-sensitive stores. This process does not involve, but is potentiated by, activation of beta-cell metabolism. Together with the known [Ca2+]i-increasing action of cAMP, our results reveal dual regulation of beta-cell [Ca2+]i by the cAMP-signaling pathway and by a physiological incretin.

Animals↗
PubMed1998

Recognition of human genes by stochastic parsing.

A gene finding system, GeneDecoder, based on a parsing technique using a stochastic grammar and dictionary of genetic words is introduced. The structure of human genes are expressed by a stochastic grammar and a dictionary, whose components are the genetic words consisting of genetic phonemes, built as hidden Markov models (HMMs). The HMMs represent the nucleotide acid bases, the codons, and the amino acids. The genetic words in the dictionary are described by the sequence of these HMMs and represent exons, introns, intergenic regions, tRNA regions and signals in DNA sequences. The statistics between these regions are expressed by the grammar, which is a stochastic network of the genetic words. Using the same kind of technique of speech recognition by HMMs with a word dictionary and a grammar, the stochastic network of genetic words enables the motif dictionary to be used during the parsing of the DNA sequences. At the same time, stochastic features of donor/acceptor sites, information of the di-codon statistics, and other important features are integrated into stochastic scores during the parsing. As a result, while the system parses DNA sequences and finds the exon/intron structures, the protein motifs are automatically annotated in the regions. It helps to identify the functions of the genes and reduces the cost of homology search for each hypothetical coding regions. This method is different from simply using the information of homology search. This method uses the information of the motif patterns during the parsing process, but searching the motif patterns after/before finding the coding regions cannot directly affect the parsing process itself. Experimental results have shown that this method reasonably finds and annotates the motifs in the exons in the DNA sequence of human.

Amino Acid Sequence↗
PubMed1997

Pituitary adenylate cyclase-activating polypeptide (PACAP) is an islet substance serving as an intra-islet amplifier of glucose-induced insulin secretion in rats.

1. We examined whether pituitary adenylate cyclase-activating polypeptide with 38 or 27 residues (PACAP-38 or PACAP-27) serves as an intra-islet regulator of glucose-induced insulin secretion in rats. PACAP antiserum specific for PACAP-38 and PACAP-27 was used to neutralize the effect of endogenous PACAP in islets. PACAP release from islets was bioassayed using the response of cytosolic Ca2+ concentration ([Ca2+]i) in single beta-cells, monitored by dual-wavelength fura-2 microfluorometry. Expression of PACAP mRNA was studied by reverse transcription-polymerase chain reaction (RT-PCR), while expression of PACAP was studied by metabolic labelling and immunoblotting. Localization of PACAP receptors was studied immunohistochemically. 2. High glucose-stimulated insulin release from isolated islets was attenuated by PACAP antiserum but not by non-immune sera. 3. The islet incubation medium with high glucose (Med) possessed a capacity, which was neutralized by PACAP antiserum, to increase [Ca2+]i in beta-cells. PACAP antiserum also neutralized the [Ca2+]i-increasing action of synthetic PACAP-38 and PACAP-27, but not that of vasoactive intestinal polypeptide (VIP) and glucagon. 4. Both Med and synthetic PACAP increased [Ca2+]i in beta-cells only in the presence of stimulatory, but not basal, glucose concentrations. In contrast, ATP, a substance that is known to be released from beta-cells, increased [Ca2+]i in beta-cells at both and stimulatory glucose concentrations. 5. Expression of PACAP mRNA and biosynthesis of PACAP-38 were detected in islets and a beta-cell line, MIN6. 6. Immunoreactivity for PACAP-selective type-I receptor was observed in islets. 7. [Ca2+]i measurements combined with immunocytochemistry with insulin antiserum revealed a substantial population of glucose-unresponsive beta-cells, many of which were recruited by PACAP-38 into [Ca2+]i responses. 8. These results indicate that PACAP-38 is a novel islet substance that is synthesized and released by islet cells and then, in an autocrine and/or paracrine manner, potentiates and arouses beta-cell responses to glucose, thereby amplifying glucose-induced insulin secretion in islets.

Adenosine Triphosphate↗
PubMed1997

Pituitary adenylate cyclase-activating polypeptide (PACAP): a novel regulator of vasopressin-containing neurons.

Pituitary adenylate cyclase-activating polypeptide (PACAP) was localized in nerve terminals that innervate arginine-vasopressin (AVP)-containing neurons in the rat hypothalamic supraoptic nucleus (SON). PACAP receptor (PACAPR) mRNA was expressed at high-levels in AVP-containing neurons in the SON, but at very low-levels in oxytocin-containing neurons. PACAPR-like immunoreactivity was found in SON and it was observed in the post-synaptic membranes as well as on the rough endoplasmic reticulum and cytoplasmic matrices in the magnocellular neurons. Doses of PACAP in the nanomolar range increased cytoplasmic Ca2+ concentrations ([Ca2+]i) in AVP-containing neurons; the increase in [Ca2+]i was inhibited by a protein kinase A blocker. These findings suggest that PACAP serves as a transmitter and/or modulator and the activation of PACAPR stimulates a cAMP-protein kinase A pathway which in turn evokes the Ca2+ signaling system. It is hypothesized that PACAP regulates the functions of AVP-containing neurons which participate in the control of plasma osmolarity and blood pressure.

Animals↗
PubMed1997

Prediction of translation initiation sites on the genome of Synechocystis sp. strain PCC6803 by Hidden Markov model.

We developed a computer program, GeneHackerTL, which predicts the most probable translation initiation site for a given nucleotide sequence. The program requires that information be extracted from the nucleotide sequence data surrounding the translation initiation sites according to the framework of the Hidden Markov Model. Since the translation initiation sites of 72 highly abundant proteins have already been assigned on the genome of Synechocystis sp. strain PCC6803 by amino-terminal analysis, we extracted necessary information for GeneHackerTL from the nucleotide sequence data. The prediction rate of the GeneHackerTL for these proteins was estimated to be 86.1%. We then used GeneHackerTL for prediction of the translation initiation sites of 24 other proteins, of which the initiation sites were not assigned experimentally, because of the lack of a potential initiation codon at the amino-terminal position. For 20 out of the 24 proteins, the initiation sites were predicted in the upstream of their amino-terminal positions. According to this assignment, the processed regions represent a typical feature of signal peptides. We could also predict multiple translation initiation sites for a particular gene for which at least two initiation sites were experimentally detected. This program would be effective for the prediction of translation initiation sites of other proteins, not only in this species but also in other prokaryotes as well.

Bacterial Proteins↗
PubMed1997

Citrulline-argininosuccinate-arginine cycle coupled to Ca2+-signaling in rat pancreatic beta-cells.

Pancreatic beta-cells possess nitric oxide (NO) synthases (NOSs) which synthesize NO and L-citrulline from L-arginine. The present study was designed to explore the mechanism of citrulline and arginine metabolism in beta-cells and its possible coupling to beta-cell functions. The enzymes involved in citrulline-arginine metabolism, argininosuccinate synthetase (ASS), argininosuccinate lyase (ASL), and NOS were expressed in rat islets and insulinoma HIT T15 cells. In the presence of stimulatory glucose, L-citrulline and L-argininosuccinate at physiological concentrations (0.1-1 mM) increased cytosolic Ca2+ concentration ([Ca2+]i) in rat beta-cells. The citrulline-induced [Ca2+]i increase was inhibited by a NOS inhibitor, N(G)-monomethyl-L-arginine (NMMA). L-citrulline also stimulated NO production in HIT cells, which was inhibited by NMMA. In conclusion, L-citrulline is metabolized by ASS-ASL-NOS cycle to produce NO, which in turn increases [Ca2+]i in beta-cells.

Animals↗
PubMed1997

Noradrenaline activates vasopressin neurons via alpha1-receptor-mediated Ca2+ signaling pathway.

Noradrenaline (NA) (1-10 microM), dibutyryl-cAMP (1-5 mM), and forskolin (10-20 microM) increased cytosolic Ca2+ concentration ([Ca2+]i) in isolated arginine-vasopressin (AVP)-containing neurons in the hypothalamic supraoptic nucleus (SON). The NA-induced increase in [Ca2+]i in AVP-containing neurons was abolished by a specific alpha1-antagonist, prazosin (1 microM) and was markedly reduced when treated with a protein kinase A (PKA) blocker, H89 (40 microM). The NA-induced [Ca2+]i was not altered by a protein kinase C (PKC) inhibitor, calphostin C (0.1 microM) and a PKC activator, TPA (100 nM). In general, NA, a known neurotransmitter in the SON, activates AVP-containing neurons via alpha1-receptor which is linked to stimulation of cAMP-PKA-regulated Ca2+ signaling pathway.

Animals↗
PubMed1997

Analysis of sequence patterns surrounding the translation initiation sites on Cyanobacterium genome using the hidden Markov model.

Sequence patterns surrounding the translation initiation sites of Cyanobacterium were precisely analyzed by the hidden Markov model (HMM) based on the actual translation initiation sites. In a previous study, 72 actual protein coding regions and their translation initiation sites on the genome of Synechocystis sp. strain PCC6803 were determined by Sazuka et al. using protein two-dimensional electrophoresis and microsequening. In this work, we extracted the sequence patterns surrounding translation initiation sites as HMM using the computer program YEBIS. The constructed HMM could recognize all but one translation initiation site. The HMM contains an AG-rich region (5.7 bp on average), as the Shine-Dalgarno sequence exclusively contains purines, upstream of the translation initiation site (-9.7 position on average) and a CT rich region (4.2 bp on average) just upstream from the translation initiation site. In addition, we found that the second amino acid (-4.5,6) could be classified into two types, one of which had C as their second codon while another of which has a nucleotide distribution relatively similar to the distribution among amino acids in the 72 proteins. This fact corresponds well to our earlier finding that when the second nucleotide of the second amino acid of a translated protein was C, an initial methionine was processed and that otherwise the methionine was intact with high frequency.

Base Sequence↗
PubMed1997

Nicotine increases cytosolic Ca2+ in vasopressin neurons.

Strong immunoreactivity for neuronal nicotinic acetylcholine receptor alpha4 subunit was detected in neurons of the supraoptic nucleus (SON). At the ultrastructural level, immunoreactivity for alpha4 was detected in the post-synaptic membranes as well as in the cytoplasmic matrices in the magnocellular neurons. Nicotine (1-10 microM) increased cytosolic Ca2+ concentrations ([Ca2+]i) in isolated arginine-vasopressin (AVP)-containing neurons in the rat SON. Nicotine (10 microM) was less potent in increasing [Ca2+]i in AVP-containing neurons than noradrenaline (1 microM), a known neurotransmitter in the SON. The nicotine-induced [Ca2+]i increase in AVP-containing neurons was markedly reduced when pre-treated with a protein kinase A (PKA) blocker, H89 (40 microM). These findings suggest that nicotine, a known neurotransmitter in the SON, activates AVP-containing neurons via nicotinic acetylcholine receptor which is linked to stimulation of cAMP-PKA-regulated Ca2+ signaling pathway.

Animals↗
PubMed1997

The ability of a new hypoglycaemic agent, A-4166, compared to sulphonylureas, to increase cytosolic Ca2+ in pancreatic beta-cells under metabolic inhibition.

1. N-(trans-4-isopropylcyclohexanecarbonyl)-D-phenylalanine (A-4166) is a new non-sulphonylurea oral hypoglycaemic agent which stimulates insulin release by increasing cytosolic Ca2+ concentration ([Ca2+]i) in beta-cells. 2. We studied comparative effects of A-4166 and sulphonylureas on [Ca2+]i, measured by dual-wavelength fura-2 microfluorometry, in single rat pancreatic beta-cells under normal conditions and conditions where glucose metabolism was inhibited. 3. A glucokinase inhibitor, mannoheptulose (10 mM), a mitochondrial respiratory inhibitor, KCN (100 microM), and uncouplers, dinitrophenol (DNP, 50 microM) and carbonyl cyanide p-trifluoromethoxyphenylhydrazone (FCCP, 0.3 microM), were used to abolish glucose-induced increases in [Ca2+]i in a reversible manner. 4. Under control conditions, A-4166 was one order more potent than tolbutamide in increasing [Ca2+]i, and maximal responses were evoked by 30 microM A-4166 and 300 microM tolbutamide. These equipotent concentrations were employed for the comparative study where glucose metabolism was inhibited. 5. In the presence of mannoheptulose, [Ca2+]i responses to tolbutamide, but not those to A-4166, were attenuated in a reversible manner. 6. KCN, DNP and FCCP inhibited [Ca2+]i responses to tolbutamide to a much greater extent than those to A-4166. Responses to tolbutamide even at 3.3 times the equipotent concentration (1000 microM) were also markedly attenuated by these inhibitors. Responses evoked by another sulphonylurea, gliclazide, were inhibited by DNP to a larger extent than A-4166-induced responses. 7. The results indicate that A-4166 acts more effectively than sulphonylureas to increase [Ca2+]i in beta-cells during metabolic inhibition.

Animals↗
PubMed1997

Comparative effects of hypotension due to isoflurane, nitroglycerin, and adenosine on subendocardial microcirculation: observation of the in situ beating swine heart under critical stenosis.

BACKGROUND: Although isoflurane may cause subendocardial hypoperfusion in the presence of coronary stenosis because of its coronary arteriolar dilatory effects, it is not known how the subendocardial microcirculation is affected. The authors examined the effects of isoflurane on poststenotic subendocardial microvessels with coronary stenosis. METHODS: The authors observed subendocardial microvessels in in situ beating swine hearts with or without critical stenosis of the left anterior descending coronary artery (LAD) with a needle-type videomicroscope during isoflurane- (ISO-H), adenosine- (ADE-H), and nitroglycerin- (NTG-H) induced hypotension (mean arterial pressure, 55 mmHg). Regional myocardial function, oxygen balance, and lactate metabolism in the region perfused by the LAD also were determined. RESULTS: In swine with stenosis, there were no differences in heart rate, cardiac output, and LAD blood flow among the three types of hypotension. Regional lactate production and anterior interventricular venous pO2 were similar during ISO-H and NTG-H but higher during ADE-H. With videomicroscopy, about half as many subendocardial microvessels could be visualized during ADE-H as with ISO-H and NTG-H. The average decrease in the systolic diameter of subendocardial microvessels of greater than 100 microm was 9 +/- 6% during ISO-H and 12 +/- 5% during NTG-H, but no consistent phasic diameter changes were observed during ADE-H. In swine without stenosis, a systolic diameter decrease was observed during all three types of hypotension. CONCLUSIONS: These findings suggest that hypotension induced by isoflurane or nitroglycerin preserves phasic diameter changes in subendocardial microvessels in the presence of critical coronary stenosis, whereas that induced by adenosine does not.

Adenosine↗
PubMed1997

Stimulatory roles of muscarinic acetylcholine receptors on T cell antigen receptor/CD3 complex-mediated interleukin-2 production in human peripheral blood lymphocytes.

It is known that there are some bidirectional interactions between the nervous and the immune systems via neurotransmitters and cytokines. To clarify whether any neurotransmitters modulate lymphocyte functions, we examined the effects of oxotremorine-M (Oxo-M) on interleukin-2 (IL-2) production in human peripheral blood lymphocytes by using enzyme-linked immunosorbent assays, Northern blot analyses, reverse transcriptase-polymerase chain reaction, and fluorescence-activated cell sorter. Pretreatment of cells with Oxo-M (10 nM to 10 microM) for 4-24 hr enhanced phytohemagglutinin (PHA)-induced IL-2 mRNA expression and markedly increased IL-2 production compared with those induced by PHA alone. Oxo-M alone did not affect IL-2 mRNA expression and IL-2 production. In CD3-positive T cells, pretreatment with Oxo-M for 24 hr enhanced PHA-induced IL-2 production. Furthermore, pretreatment with Oxo-M enhanced PHA-induced mRNA expression of the alpha and beta subunits of IL-2 receptors and DNA synthesis. Cytometric analysis showed Oxo-M treatment did not up-regulate expression of cell surface molecules such as CD3, CD2, CD4, CD8, and IL-2 receptors. These results suggest that activation of muscarinic receptors enhances T cell antigen receptor/CD3-induced IL-2 production.

Antigens, CD↗