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T Yada

Publications and source records attributed to T Yada.

At least 91 records · Page 5Linked to original sources
PubMed1997

Direct stimulation of basal insulin secretion by physiological concentrations of leptin in pancreatic beta cells.

We examined a possible mechanism underlying the link between obesity and hyperinsulinemia, focusing on leptin, a peptide released from adipocytes which affects the satiety center in the brain. The leptin receptor isoforms, Ob-Ra and Ob-Rb, are present in the pancreatic beta cell line MIN6 and in rat pancreatic islets, based on RT-PCR. A 2 hr, but not a 30 min, incubation with 1 nM recombinant mouse leptin, the concentration observed in obese subjects, stimulated basal (at 5 mM glucose) insulin secretion by approximately 40% in both MIN6 and rat islets. Stimulatory effects were not observed without glucose or when the incubation medium containing 1 nM leptin had been preincubated with the immobilized leptin antibody. In contrast to the stimulatory effects on basal insulin secretion at 1 nM, the maximally stimulated insulin secretion at 25 mM glucose was not significantly changed by 1 nM leptin in isolated rat islets. In addition, 10 and 100 nM leptin exerted small but significant inhibitory effects on 16.7 mM glucose-stimulated insulin secretion. Thus, leptin acts directly on pancreatic beta cells, and stimulation of basal insulin secretion by physiological concentrations of leptin may account in part for the fasting hyperinsulinemia observed in obese subjects.

Animals↗
PubMed1997

Automatic Gene Recognition without Using Training Data.

In this paper, we propose a new approach for gene recognition, which uses no training data for the recognizer. In this approach, we start from a simple model, which only uses the knowledge of start codons and the stop codons, then the recognition of the DNA sequences by the recognizer and the training of the parameters of the recognizer by the result of the recognition are repeated. We applied this parse and train approach to the complete genome sequence of cyanobacterium, and achieved the almost same recognition rate with the case of using the whole sequence as training data. This results open the possibility to use automatic gene annotation system in the early stage of sequencing projects.

Journal Article↗
PubMed1997

Functional prediction of B. subtilis genes from their regulatory sequences.

In bacterial cells, gene expression is regulated by multiple sigma factors, each of which has its promoter specificity, according to their conditions. Thus, if we can discriminate which sigma factor binds to the upstream region of a given coding sequence, we can predict in what condition it will be expressed. In this paper, we show this approach is feasible for the analysis of Bacillus subtilis genome. Based on our collection of known promoter sequences, we prepared 8 predictors to characterize known sigma factors using the hidden Markov model and their prediction accuracies were estimated with a cross-validation test. Furthermore, we predicted the sigma-dependencies for each of 1415 candidate genes in the genome. Our prediction results are experimentally testable and seem useful for the post-sequencing project.

Bacillus subtilis↗
PubMed1996

Detection of short protein coding regions within the cyanobacterium genome: application of the hidden Markov model.

The gene-finding programs developed so far have not paid much attention to the detection of short protein coding regions (CDSs). However, the detection of short CDSs is important for the study of photosynthesis. We utilized GeneHacker, a gene-finding program based on the hidden Markov model (HMM), to detect short CDSs (from 90 to 300 bases) in a 1.0 mega contiguous sequence of cyanobacterium Synechocystis sp. strain PCC6803 which carries a complete set of genes for oxygenic photosynthesis. GeneHacker differs from other gene-finding programs based on the HMM in that it utilizes di-codon statistics as well. GeneHacker successfully detected seven out of the eight short CDSs annotated in this sequence and was clearly superior to GeneMark in this range of length. GeneHacker detected 94 potentially new CDSs, 9 of which have counterparts in the genetic databases. Four of the nine CDSs were less than 150 bases and were photosynthesis-related genes. The results show the effectiveness of GeneHacker in detecting very short CDSs corresponding to genes.

Algorithms↗
PubMed1996

Current status of PACAP as a regulator of insulin secretion in pancreatic islets.

PACAP-27 and PACAP-38 as low as 10(-13) M stimulate insulin release from rat islets in a glucose-dependent manner. PACAP also glucose dependently increases cAMP and [Ca2+]i in rat islet beta cells. The [Ca2+]i and insulin secretory responses to PACAP exhibit a similar concentration-response relationship, exhibiting a peak at 10(-13) M. When the [Ca2+]i response is abolished by nitrendipine, a blocker of L-type Ca2+ channels, the insulin response is also inhibited. Insulinotropic peptides glucagon, GLP-1, and VIP also increase [Ca2+]i in beta cells, but only in the nanomolar concentration range. PACAP is 4 logs more potent that VIP, a peptide that exhibits 68% amino acid homology and shares the type II PACAP receptor with PACAP. Immunoreactivity for the type I PACAP receptor is demonstrated in rat islets. Furthermore, PACAP immunoreactivity is demonstrated in nerve fibers and islets in rat pancreas. Based on these findings, we can draw the following conclusions: (1) PACAP is localized in pancreatic nerve fibers and islets; (2) PACAP in the subpicomolar range stimulates insulin release from islets; (3) the stimulation of insulin release is mediated by the cAMP-dependent increase in [Ca2+]i in beta cells; (4) all the PACAP effects are glucose-dependent; (5) PACAP is the most potent insulinotropic hormone known, and (6) the type I PACAP receptor appears to mediate the action of PACAP in the subpicomolar range. Finally, we hypothesize that PACAP is a pancreatic peptide of both neural and islet origin and functions as an intrinsic potentiator of glucose-induced insulin secretion in pancreatic islets (FIG 6).

Animals↗
PubMed1996

Effects of intraaortic balloon pumping on septal arterial blood flow velocity waveform during severe left main coronary artery stenosis.

OBJECTIVES: We sought to evaluate the effect of intraaortic balloon pumping on the phasic blood velocity waveform into myocardium with severe coronary artery stenosis. BACKGROUND: In the presence of severe coronary artery stenosis, it is not clear whether intraaortic balloon pumping augments intramyocardial inflow during diastole or changes systolic retrograde blood flow from the myocardium to the extramural coronary arteries. METHODS: Using anesthetized open chest dogs (n=7), we introduced severe stenosis in the left main coronary artery to reduce the poststenotic pressure to approximately 60 mm Hg (>90% diameter stenosis). Septal arterial blood flow velocities were measured with a 20-MHz, 80-channel ultrasound pulsed Doppler velocimeter. Left anterior descending arterial flow, aortic pressure and poststenotic distal coronary pressure were measured simultaneously. The diastolic anterograde flow integral and systolic retrograde flow integral were compared in the presence and absence of intraaortic balloon pumping. RESULTS: Although intraaortic balloon pumping augmented diastolic aortic pressure, this pressure increase was not effectively transmitted through stenosis. Septal arterial diastolic flow velocity was not augmented, and left anterior descending arterial flow was unchanged during intraaortic balloon pumping. CONCLUSIONS: In the presence of severe coronary artery stenosis, intraaortic balloon pumping failed to increase diastolic inflow in the myocardium and did not enhance systolic retrograde flow from the myocardium to the extramural coronary artery. Thus, the major effect of intraaortic balloon pumping on the ischemic heart with severe coronary artery stenosis may be achieved by reducing oxygen demand by systolic unloading.

Analysis of Variance↗
PubMed1996

Somatostatin and insulin secretion due to common mechanisms by a new hypoglycemic agent, A-4166, in perfused rat pancreas.

N-[(trans-4-isopropylcyclohexyl)-carbonyl]-D-phenylalanine (A-4166) is a nonsulfonylurea hypoglycemic agent that decreases blood glucose levels in nondiabetic and diabetic animals. In the present study, we attempted to determine the effect of A-4166 on hormone secretion from the in vitro-perfused rat pancreas and to examine the underlying secretory mechanisms. In the presence of basal glucose (3 mmol/L), A-4166 markedly stimulated insulin and somatostatin release in a concentration-dependent manner over 0.03 to 3 mmol/L. A sulfonylurea, tolbutamide, also stimulated insulin and somatostatin release. A-4166 and tolbutamide elevated the level of glucagon release; however, the change lacked a clear concentration-dependent property. A-4166 at 0.3 mmol/L and tolbutamide at 3 mmol/L exhibited maximal stimulation of insulin release to a similar extent, indicating that A-4166 is one log-order more potent than and as effective as tolbutamide. By contrast, A-4166 stimulated somatostatin release to a threefold greater extent than tolbutamide. A-4166 evoked an increase in the cytosolic free-Ca2+ concentration ([Ca2+]i) in rat pancreatic beta cells. [Ca2+]i and insulin secretory responses to A-4166 were inhibited by nitrendipine (NTD), a blocker of the L-type Ca2+ channel, and by diazoxide (DAZ), an opener of the adenosine triphosphate (ATP)-sensitive K+ channel. Furthermore, A-4166-stimulated somatostatin release was also inhibited by NTD and by DAZ. The results indicate that A-4166 and tolbutamide stimulate the release of insulin and somatostatin, and that A-4166 is much more effective than tolbutamide in releasing somatostatin, a hormone that attenuates hyperglycemia under certain circumstances. It is concluded that A-4166-induced insulin release is mediated by an increase in [Ca2+]i in beta cells. An inhibition of ATP-sensitive K+ channels and a consequent activation of L-type Ca2+ channels appear to play a key role not only in insulin secretion from beta cells, but also in somatostatin secretion from delta cells in response to A-4166.

Adenosine Triphosphate↗
PubMed1996

Transient accumulation of perisinusoidal chondroitin sulfate proteoglycans during liver regeneration and development.

After partial hepatectomy, the liver is capable of complete restoration of normal hepatic size, architecture, and function (regeneration). To study roles of the extracellular matrix in regeneration, the temporal and spatial sequences of deposition of several components, including collagen I, III, and IV, fibronectin, laminin, heparan sulfate proteoglycan (perlecan), and chondroitin sulfate proteoglycans were characterized by light microscopic immunohistochemistry in rat liver after 70% partial hepatectomy. Consistent with previous reports, there was a brisk mitosis of hepatocytes after the partial hepatectomy. Of the extracellular matrix components studied, 1B5 epitope generated by chondroitinase ABC digestion on chondroitin sulfate proteoglycans exhibited the most dramatic changes; the epitope was detectable as early as 1.5 hr after partial hepatectomy and its immunoreactivity reached a maximum at 24 hr, then declined gradually. This transient expression of the 1B5 epitope was also detected in neonatal rat liver during development. By Western blotting, the 1B5 epitope was found on two forms of the core protein of chondroitin sulfate proteoglycans with apparent molecular masses of 163 KD and 152 KD, which were also regulated in the same temporal manner.

Animals↗
PubMed1996

cAMP-signaling pathway acts in selective synergism with glucose or tolbutamide to increase cytosolic Ca2+ in rat pancreatic beta-cells.

cAMP and the insulinotropic peptides that raise cAMP glucose-dependently increase the cytosolic free Ca2+ concentration ([Ca2+]i) in pancreatic beta-cells, which is tightly linked to the potentiation of glucose-induced insulin release. We examined whether cAMP increases [Ca2+]i in specific cooperation only with glucose or also with other insulin secretagogues that act through different mechanisms. [Ca2+]i in single rat pancreatic beta-cells was measured by dual-wavelength fura-2 microfluorometry. In the presence of a stimulatory concentration of glucose (8.3 mmol/l) and the moderate elevation in [Ca2+]i induced by it, forskolin, an activator of adenylyl cyclase, or dibutyryl cAMP produced a marked additional increase in [Ca2+]i but was ineffective at the basal 2.8 mmol/l glucose. These cAMP-elevating agents also potentiated the effect of tolbutamide on [Ca2+]i. The cAMP-induced increase in [Ca2+]i was completely and selectively inhibited by a blocker of cAMP-dependent protein kinase A (PKA), and by nitrendipine, a blocker of the L-type Ca2+ channel. However, in the presence of high KCl and the [Ca2+]i elevation induced by it, a rise in cAMP failed to further increase [Ca2+]i, whereas BAY K8644, an agonist of L-type Ca2+ channels, evoked an additional increase in [Ca2+]i. Under low Na+ conditions, the [Ca2+]i response to cAMP was observed in the majority of the cells. In the cells in which glucose at 4.5-5 mmol/l was inadequate to increase [Ca2+]i, the glucose together with a rise in cAMP often increased [Ca2+]i. Likewise, tolbutamide and a rise in cAMP acted in concert to increase [Ca2+]i. Thus, cAMP left-shifted the concentration-[Ca2+]i response relationship for glucose and tolbutamide. In conclusion, the cAMP-PKA pathway acts in selective synergism with glucose and tolbutamide to initiate [Ca2+]i signals in pancreatic beta- cells. cAMP appears to regulate beta-cell sensitivity to glucose and tolbutamide. In contrast, cAMP fails to cooperate with high KCl to increase [Ca2+]i. It is suggested that cAMP acts mainly on a site that is more proximal but functionally linked to the L-type Ca2+ channel, thereby finally increasing Ca2+ influx through this channel.

Animals↗
PubMed1996

Gene recognition in cyanobacterium genomic sequence data using the hidden Markov model.

We have developed a hidden Markov model (HMM) to detect the protein coding regions within one megabase contiguous sequence data, registered in a database called GenBank in eight entries, of the genome of cyanobacterium, Synechocystis sp. strain PCC6803. Detection of the coding regions in the database entry was performed by using HMM whose parameters were determined by taking the statistics from the rests of the entries. This HMM has states modeling the di-codons and their frequencies within coding regions and those modeling its base contents in the intergenic regions. Results of the cross-validation showed that the HMM recognized 92.1% of coding regions assigned in sequence annotation. In addition, it suggested 94 potential new coding regions whose length are longer than 90 bases. The recognition accuracy calculated at the level of individual bases was 90.7% for the coding regions and 88.1% for the intergenic regions. This corresponds to a correlation coefficient for coding region recognition of 0.784. Comparison with its prediction accuracy with that by GeneMark showed that the HMM has the same level of prediction accuracy as GeneMark on average. Since we can extend the HMM to utilize information such as SD sequences, the prediction accuracy of the HMM will be enhanced. It was observed that correlation was positive between the prediction rate of the coding regions and the G + C content at the third position of the codon. This suggests the possibility that the prediction rate of coding regions in the cyanobacteria sequence can be enhanced by improving the present HMM into that reflects the classification of coding regions based on the G + C content.

Cyanobacteria↗
PubMed1996

Extraction of hidden Markov model representations of signal patterns in DNA sequences.

We have developed a method to extract the signal patterns in DNA sequences. In this method, the Genetic Algorithm (GA) and Baum-Welch algorithm are used to obtain the best Hidden Markov Model (HMM) representations of the signal patterns in DNA sequences. The GA is used to search the best network shapes and the initial parameters of the HMMs. Baum-Welch algorithm is used to optimize the HMM parameters for the given network shapes. Akaike Information Criterion (AIC), which gives a criterion for the balance of adaptation and complexity of a model, is applied in the HMM evaluation. We have applied the method to the extraction of the signal patterns in human promoters and 5' ends of yeast introns. As a result, we obtained HMM representations of characteristic features in these sequences. To validate the efficiency of the method, we have performed promoter recognition using obtained HMMs. Two entries including nine promoters are selected from GenBank 76.0, and it is observed that the HMM can predicts eight promoters correctly. These results imply that the method is efficient to design preferable HMM networks, and provides reliable models for the recognition of the signal patterns.

Algorithms↗
PubMed1995

Two distinct modes of Ca2+ signalling by ACh in rat pancreatic beta-cells: concentration, glucose dependence and Ca2+ origin.

1. Calcium signalling by acetylcholine (ACh) in single rat pancreatic beta-cells was studied. The cytosolic free Ca2+ concentration ([Ca2+]i) was measured by dual-wavelength fura-2 microfluorometry. 2. In the presence of basal glucose (2.8 mM), 10(-6) to 10(-4) M ACh (high ACh) transiently increased [Ca2+]i. The [Ca2+]i response to 10(-5) M ACh was little altered under Ca(2+)-free conditions. Brief pulses of 10(-5) M ACh evoked successive [Ca2+]i responses, which were progressively inhibited by 0.2-0.5 microM thapsigargin, a specific inhibitor of the endoplasmic reticulum (ER) Ca2+ pump. 3. Elevation of glucose to 8.3 mM, a concentration which stimulates insulin release, increased [Ca2+]i to an initial peak followed by a sustained, moderate elevation. Addition of 10(-8) to 10(-7) M ACh (low ACh) evoked a further increase in [Ca2+]i. The [Ca2+]i response to 10(-7) M ACh was completely inhibited under Ca(2+)-free conditions by 1 microM nitrendipine, a blocker of L-type Ca2+ channels, and by 100 microM diazoxide, an opener of ATP-sensitive K+ channels. 4. In the presence of 8.3 mM glucose, [Ca2+]i responses to 10(-5) M ACh were reduced but not abolished by Ca(2+)-free conditions, nitrendipine and diazoxide. Successive [Ca2+]i transients induced by 10(-5) M ACh pulses in the presence of nitrendipine were progressively inhibited by thapsigargin. 5. The results revealed two distinct modes of Ca2+ signalling: low ACh increases [Ca2+]i by stimulating Ca2+ influx through voltage-dependent L-type Ca2+ channels only in the beta-cells in which glucose has already elevated [Ca2+]i, while high ACh increases [Ca2+]i at basal as well as stimulatory glucose concentrations by releasing Ca2+ from the ER. The former mechanism is likely to relate to the potentiator action and the latter to the initiator action of ACh on insulin release. High ACh and elevated glucose provoke both modes of Ca2+ signalling.

Acetylcholine↗
PubMed1995

Effects of thapsigargin, an intracellular CA2+ pump inhibitor, on insulin release by rat pancreatic B-cell.

This is the first report as to the effects of thapsigargin (Tg), an inhibitor of intracellular Ca2+ pumps, on insulin release by pancreatic B-cells. Tg does not alter basal insulin release by the isolated islets, with 3 mM glucose. However, it potentiates high glucose-induced insulin release: potentiation of the first phase response is dose-related in a concentration range of 1.3-40 microM. In isolated B-cells, Tg causes a minimal rise in basal cytosolic free calcium concentration ([Ca2+]i) and eliminates high glucose-induced initial lowering of [Ca2+]i. Tg does not alter glucose oxidation by the islets and the islet insulin content. An elimination of glucose-induced sequestration of Ca2+ into Tg-sensitive intracellular pool(s) is considered to be the cause of Tg potentiation of glucose effect on insulin release.

Animals↗
PubMed1995

Interplay of glucose-stimulated Ca2+ sequestration and acetylcholine-induced Ca2+ release at the endoplasmic reticulum in rat pancreatic beta-cells.

It is known that the stimulation with high glucose initially decreases as well as subsequently increases the cytosolic free Ca2+ concentration ([Ca2+]i) in pancreatic beta-cells. In the present study, we aimed at exploring the ionic mechanism and physiological role of the glucose-induced decrease in [Ca2+]i by measuring [Ca2+]i in single pancreatic beta-cells from normal rats. The glucose-induced decrease in [Ca2+]i in beta-cells was completely inhibited by thapsigargin (Tg), a specific inhibitor of the endoplasmic reticulum (ER) Ca2+ pump (Ca(2+)-ATPase). On the other hand, neither a Ca(2+)-free nor a low-Na+ condition significantly altered the glucose-induced decrease in [Ca2+]i. At basal glucose concentrations (1-4.5 mM), an insulin secretagogue acetylcholine (ACh) evoked a rather transient increase in [Ca2+]i in the presence and absence of extracellular Ca2+. A rise in glucose concentration from 1 to 4.5 mM produced a sustained decrease in [Ca2+]i and concomitantly augmented the ACh-evoked increase in [Ca2+]i. The resting [Ca2+]i level determined by glucose was tightly and reciprocally correlated with the peak of the [Ca2+]i response to ACh. Successive ACh pulses elicited repeated [Ca2+]i responses, which were progressively inhibited by Tg, suggesting that Ca2+ released by ACh was taken up by the ER Ca2+ pump and thus cycled. The results demonstrate that glucose decreases [Ca2+]i in pancreatic beta-cells mainly by activating the Ca2+ pump in ER from which ACh mobilizes Ca2+. Furthermore, the glucose-stimulated sequestration of Ca2+ by ER results in an augmented [Ca2+]i response to ACh, providing a mechanistic basis for the glucose-dependent action of ACh to initiate insulin secretion.

Acetylcholine↗