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Biomedical subjects

Y Toya

Publications and source records attributed to Y Toya.

At least 37 records · Page 2Linked to original sources
PubMed1998

Activation of angiotensinogen gene in cardiac myocytes by angiotensin II and mechanical stretch.

Circulating and cardiac renin-angiotensin systems (RAS) play important roles in the development of cardiac hypertrophy. Mechanical stretch of cardiac myocytes induces secretion of ANG II and evokes hypertrophic responses. Angiotensinogen is a unique substrate of the RAS. This study was performed to examine the regulation of the angiotensinogen gene in cardiac myocytes in response to ANG II and stretch. ANG II and stretch significantly increased the levels of angiotensinogen mRNA in cardiac myocytes. Actinomycin D completely inhibited ANG II- and stretch-mediated increases in angiotensinogen mRNA. Although CV-11974 abolished ANG II-mediated increases in mRNA level and promoter activity of the angiotensinogen gene, the inhibition of stretch-mediated activation by CV-11974 was significant but not complete. These results indicate that ANG II activates transcription of the angiotensinogen gene exclusively via ANG II type 1-receptor pathway and that stretch activates such transcription mainly via the same pathway in cardiac myocytes. Furthermore, factors other than ANG II may also be involved in stretch-mediated activation of the angiotensinogen gene in cardiac myocytes.

Angiotensin II↗
PubMed1998

Inhibition of adenylyl cyclase by caveolin peptides.

Caveolae and their principal component caveolin have been implicated in playing a major role in G protein-mediated transmembrane signaling. We examined whether caveolin interacts with adenylyl cyclase, an effector of G protein signaling, using a 20-mer peptide derived from the N-terminus scaffolding domain of caveolin-1. When tissue adenylyl cyclases were examined, cardiac adenylyl cyclase was inhibited more potently than other tissue adenylyl cyclases. The caveolin-1 peptide inhibited type V, as well as type III adenylyl cyclase, overexpressed in insect cells, whereas the same peptide had no effect on type II. The caveolin-3 scaffolding domain peptide similarly inhibited type V adenylyl cyclase. In contrast, peptides derived from the caveolin-2 scaffolding domain and a caveolin-1 nonscaffolding domain had no effect. Kinetic studies showed that the caveolin-1 peptide decreased the maximal rate (Vmax) value of type V without changing the Michaelis constant (Km) value for the substrate ATP. Studies with various truncations and point mutations of this peptide revealed that a minimum of 16 amino acid residues and intact aromatic residues are important for the inhibitory effect. The potency of inhibition was greater when adenylyl cyclase was in stimulated condition vs. basal condition. Thus, caveolin may be another cellular component that regulates adenylyl cyclase catalytic activity. Our results also suggest that the caveolin peptide may be used as an isoform-selective inhibitor of adenylyl cyclase.

Adenylyl Cyclase Inhibitors↗
PubMed1997

Regulation of adenylyl cyclase isoforms by N-alkanols.

We examined the effect of n-alkanols on adenylyl cyclase isoforms (types II and V) overexpressed in insect cells. Ethanol stimulated the type II isoform but not the type V isoform. Ethanol stimulated type II adenylyl cyclase greater than GTP gamma S, and the treatment of the membrane with GDP beta S or cholera toxin did not affect this stimulation. Other n-alkanols inhibited type V adenylyl cyclase activity in proportion to their lipophilic potency. In contrast, type II adenylyl cyclase was stimulated by weakly lipophilic n-alkanols and inhibited by strongly lipophilic n-alkanols. When solubilized membranes and purified preparations were used, all the n-alkanols inhibited type II adenylyl cyclase. Our data suggest that n-alkanols regulated adenylyl cyclase isoform-dependently. Stimulation of the type II isoform was independent from the interaction with Gs alpha but required the presence of an intact membrane structure. Our study may provide another step to understanding how membrane protein subtypes are differentially regulated by n-alkanols.

Adenylyl Cyclase Inhibitors↗
PubMed1997

Isoform-dependent activation of adenylyl cyclase by proteolysis.

Recent findings have suggested that the cellular proteolytic system plays a major role in the regulation of various intra- and extra-cellular signaling. It was previously shown that proteolytic treatment of adenylyl cyclase leads to the activation of this enzyme. We demonstrate that this activation occurs in an adenylyl cyclase isoform-dependent manner. The type II isoform was strongly activated (approximately 500%), the type III isoform was modestly activated (approximately 30%),and the type V isoform was inhibited by trypsin. Activation of type II adenylyl cyclase occurred in trypsin dose- and time-dependent manners and was blocked by a trypsin inhibitor in a dose-dependent manner. Other proteases, such as thrombin and plasminogen, similarly activated the type II isoform, but not the others. Our data suggest that proteolytic activation is an isoform- and thus cell type-dependent mechanism of altering adenylyl cyclase catalytic activity.

Adenylyl Cyclases↗
PubMed1997

Isoform-specific regulation of adenylyl cyclase by oxidized catecholamines.

Both epinephrine and manganese are known to stimulate cAMP production in cardiac homogenates. When added together, however, they inhibited adenylyl cyclase catalytic activity. Type V adenylyl cyclase, the major isoform in the heart, was also inhibited when an increasing concentration of epinephrine was added in the presence of manganese. Inhibition was not dependent on the condition of stimulation or preparation of the enzyme. However, this inhibition was abolished in the presence of anti-oxidant. Other catecholamines, including dopamine and isoproterenol, as well as adrenochrome, an oxidized product of epinephrine, similarly inhibited the activity of this enzyme. Kinetic analyses revealed that the K(m) for the substrate ATP was unchanged, but the V(max) was significantly decreased. In contrast, type II adenylyl cyclase, a non-cardiac isoform, was resistant to such inhibition by adrenochrome and was somewhat stimulated by it. Thus, catecholamines, when oxidized, directly interacted with adenylyl cyclase in an isoform-specific manner in the absence of G proteins. Our findings suggest that adenylyl cyclase isoforms have different sensitivity to various stresses, including oxidative stress.

Adenylyl Cyclases↗
PubMed1997

Downregulation of caveolin by chronic beta-adrenergic receptor stimulation in mice.

Caveolae, flask-shaped invaginations of cell membranes, are believed to play pivotal roles in transmembrane transportation of molecules and cellular signaling. Caveolin, a structural component of caveolae, interacts directly with G proteins and regulates their function. We investigated the effect of chronic beta-adrenergic receptor stimulation on the expression of caveolin subtypes in mouse hearts by immunoblotting and Northern blotting. Caveolin-1 and -3 were abundantly expressed in the heart and skeletal muscles, but not in the brain. Continuous (-)-isoproterenol, but not (+)-isoproterenol, infusion via osmotic minipump (30 micrograms.g-1.day-1) for 13 days significantly downregulated both caveolin subtypes in the heart. The expression of caveolin-1 was reduced by 48 +/- 6.1% and that of caveolin-3 by 28 +/- 4.0% (P < 0.01, n = 8 for each). The subcellular distribution of caveolin subtypes in ventricular myocardium was not altered as determined by sucrose gradient fractionation. In contrast, the expression of both caveolin subtypes in skeletal muscles was not significantly changed. Our data suggest that the expression of caveolin subtypes is regulated by beta-adrenergic receptor stimulation in the heart.

Adrenergic beta-Agonists↗
PubMed1997

[Catecholamine and dopamine].

Almost all the genes of the enzymes which synthesize and metabolize the catecholamines (dopamine, norepinephrine, epinephrine) have been cloned and the gene targeting technology have been applied to introduce the gene knockout mouse such as thyrosine hydroxylase and dopamine beta hydroxylase. At least nine adrenergic receptors and five dopamine receptors have been cloned, which include alpha 1A-, alpha 1 B-, alpha 1 D-, alpha 2 A-, alpha 2B-, alpha 2C-, beta 1-, beta 2-, beta 3-adrenergic receptors and D1-, D2-, D3-, D4-, D5-dopamine receptors. Transgenic mouse as well as gene knockout mouse of these genes have been also produced. Furthermore, intracellular signal transduction systems of the catecholamines have been clarified using molecular techniques, including nine subtypes of adenylyl cyclase. Using these cloned genes and transgenic and gene knockout mouse, more detailed features of the catecholamine systems and those receptors and intracellular signal transduction systems will be clarified in near future.

Adenylyl Cyclases↗
PubMed1996

Soluble adenylyl cyclase from Spodoptera frugiperda (Sf9) cells. Purification and biochemical characterization.

An insect ovarian cell, Spodoptera frugiperda (Sf9), has been widely used to express recombinant proteins, including adenylyl cyclase, as a host cell in the baculovirus expression system. We report the presence and characterization of a soluble adenylyl cyclase (sAC) distinct from a membrane-bound form of adenylyl cyclase (mAC) that is also present in Sf9 cells. sAC was purified 3,500-fold to near homogeneity; a single band at 25 kDa on SDS-polyacrylamide gel electrophoresis correlated well with adenylyl cyclase catalytic activity. The purified enzyme had a catalytic activity of 0.1 micromol/min.mg and the Km of 0.55 mM for the substrate ATP. In contrast to mAC, sAC was heat-stable. Enzymatic activity of sAC was not stimulated by forskolin and was inhibited by salts at high concentrations. sAC utilized both manganese- and magnesium-ATP as substrate. Di- or triphosphate-containing nucleotides, such as GTP and GDP, as well as pyrophosphate, noncompetitively inhibited sAC. Our data suggest that the physical and biochemical characteristics of sAC are different from those of mAC in Sf9 cells as well as from those of other known forms of adenylyl cyclase in animal cells; sAC in Sf9 cells may constitute a new member of adenylyl cyclase found in animals.

Adenylyl Cyclase Inhibitors↗
PubMed1996

Regulation of type V adenylyl cyclase by PMA-sensitive and -insensitive protein kinase C isoenzymes in intact cells.

Abstract Type V adenylyl cyclase (AC) was stably over-expressed in HEK293 cells (293AC-V). Forskolin-stimulated cAMP accumulation in 293AC-V was 5 times as great as that in control cells. PMA, a protein kinase C (PKC) activator, enhanced cAMP accumulation in 293AC-V cells dose-and time-dependently and this enhancement was abolished by staurosporine. Insulin also enhanced cAMP accumulation in 293AC-V cells. Co-transfection of PKC-zeta, but not PKC-alpha, potentiated the effects of insulin. These data suggest that type V AC activity is regulated in cells by PKC isoenzymes through different extracellular stimuli.

Adenylyl Cyclases↗
PubMed1996

Adenosine A1 receptor and its gene expression in ventricles from spontaneously hypertensive rats.

We characterized the adenosine A1 receptor and the levels of its mRNA expression in the ventricles of 6- and 13-wk-old Wistar-Kyoto rats (WKY) and spontaneously hypertensive rats (SHR). The binding of 2-chloro-[3H]cyclopentyladenosine ([3H]CCPA), an A1 agonist ligand, to ventricular membranes was saturable and reversible. The receptor density was significantly lower in SHR than in WKY at 13 wk. The dissociation constant values were not different among these groups. In Northern blot analysis using rat A1 receptor cDNA, levels of mRNA did not differ significantly in the two groups at 13 wk, but the level in SHR significantly exceeded that in WKY at 6 wk. Because plasma adenosine levels were reported to be increased at 13 wk in SHR and we found mRNA levels were similar at this age, the discrepancy between A1 receptor density and its mRNA levels might be related to the desensitization of A1 receptors. Although the implication of this decreased density of A1 receptors is not known, it may involve an increased susceptibility to ischemia.

Animals↗
PubMed1995

Alpha 1-adrenergic receptors in cardiac ventricles of Dahl rats.

This study was designed to examine the effects of sex, age, and a high-salt diet on cardiac alpha 1-adrenoceptors in an animal model of genetic hypertension, the Dahl salt-sensitive rat. Ventricular alpha 1-adrenoceptors were measured by radioligand binding with [3H]prazosin in membrane fractions in Dahl S and R rats of 7, 12, and 15 weeks of age. In both S and R rats, the maximal binding (Bmax) of alpha 1-adrenoceptor binding was greater in male than in female rats. The Bmax decreased with age in both the S and R strains; at 12 weeks of age, Bmax was approximately one-half of that observed at 7 weeks of age in both S and R strains. In the rats fed a high-salt diet, the Bmax tended to be greater in S rats than in R rats at 12 weeks of age and this difference became significant at 15 weeks of age. A significant positive correlation was found between the Bmax and the heart-to-body weight ratio in the Dahl S and R rats. The dissociation constant (Kd) was not different between male S and R rats at each age. These results suggest that the ventricular alpha 1-adrenoceptor may be involved in cardiac hypertrophy in Dahl rats.

Aging↗
PubMed1994

Identification of adenosine A2 receptor-cAMP system in human aortic endothelial cells.

The involvement of endothelial adenosine A2 receptor-cAMP system in A2 receptor-mediated vasodilation in human aortic endothelial cells (HAEC) was investigated. Reverse transcription-polymerase chain reaction (RT-PCR) revealed the expression of both A2a and A2b receptors mRNA in HAEC. In HAEC, YT-146 (selective A2 receptor-agonist) produced a dose-dependent increase of cAMP production. This increase was inhibited by theophylline. YT-146 also showed a vasodilatory action in isolated rat aorta. The removal of endothelium significantly attenuated this vasodilatory effect. Our results provide the first evidence for the expression of both subtypes of the A2a and A2b receptors which regulate cAMP production in human endothelial cells. The present results also suggest that A2 receptor-cAMP system was involved in the endothelium-dependent vasodilatory actions and may play important roles in regulating vascular functions of HAEC.

Acetylcholine↗
PubMed1994

Antihypertensive effects of 2-octynyladenosine (YT-146), a selective adenosine A2 receptor agonist, in Dahl salt-sensitive rats.

The antihypertensive effects of a novel adenosine A2 receptor agonist, 2-octynyl adenosine (YT-146), were evaluated in Dahl salt-sensitive rats. After rats were fed a high-salt (8% NaCl) diet for 2 or 3 weeks, they received oral YT-146 (0.1 or 1.0 mg/kg) or vehicle as a single dose (acute study) or once daily for 10 days (chronic study). In the acute study, tail-cuff blood pressure (BP) and pulse rate (PR) were measured before and 3, 6, and 24 h after administration, and blood samples were collected 3 h after administration. In the chronic study, BP and PR were measured 3 and 24 h after administration and urine was collected for 24 h on day 9. Blood samples were also collected 3 h after administration on day 10. BP was significantly lowered by 1.0 mg/kg of YT-146 in either the acute study (from 184 +/- 3 to 152 +/- 5 mm Hg, P < .01) or the chronic study (from 226 +/- 4 to 201 +/- 2 mm Hg, P < .01), while an increase in PR was not observed (acute study: from 382 +/- 8 to 366 +/- 3 beats/min; chronic study: from 420 +/- 8 to 411 +/- 8 beats/min). YT-146 had no effect on plasma renin activity (PRA), plasma aldosterone, vasopressin (ADH), and atrial natriuretic peptide (ANP) in the acute study.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine↗
PubMed1994

Slow hemodialysis performed during the day in managing renal failure in critically ill patients.

Slow hemodialysis (HD) was performed for 10 h during the day in 11 critically ill patients with renal failure. The dialysis method was a modification of the pump-driven continuous venovenous HD. A nonsterile bicarbonate-containing hemodialysate was passed into the EVAL membrane dialyzer at a flow rate of 30 ml/min. No patient developed further hemodynamic instability during the treatment. The serum urea level was maintained below 20 mmol/l within 4 days of initiating the treatment. It allowed the patients to rest without interruption at night. This method was safely conducted by general nursing staff under the supervision of nephrologists on duty during the day. This schedule offers an approach to renal replacement therapy for hemodynamically unstable patients without any potential problem in the extracorporeal circulation at night.

Acute Kidney Injury↗
PubMed1994

Association analysis of restriction fragment length polymorphism for alpha 2-adrenergic receptor genes in essential hypertension in Japan.

Recently, restriction fragment length polymorphism (RFLP) of alpha 2-adrenergic receptor gene (alpha 2-C10) digested with Bsu36I restriction enzyme has been reported in US populations. Therefore, we examined the association of this RFLP with essential hypertension by comparing the frequency of specific alleles for this gene in Japanese populations. The distribution of this RFLP was compared with that in US populations. Subjects were hypertensive patients with a family history of essential hypertension (n = 56) and normotensive subjects whose parents had no history of essential hypertension (n = 46). DNA was prepared from leukocytes. RFLP was determined by use of Southern blot analysis with an alpha 2-C10 probe and Bsu36I. The frequencies of the major (12-kb) and minor (5.8-kb) alleles were 0.30 and 0.70 in hypertensive patients and 0.38 and 0.62 in normotensive subjects, respectively. The difference between observed alleles in all subjects in each group was not significant (chi 2 = 1.33, P > .1). The difference between the overall allelic frequency in Japan and that reported in US populations was significant. This study found no evidence for an association between alpha 2-adrenergic receptor gene/Bsu36I RFLP and essential hypertension in Japan. However, the findings showed that the allele frequency in Japan differed from that reported in US populations.

Adult↗
PubMed1994

Cardiac pheochromocytoma. A case report and review of the literature.

A case of intrapericardial pheochromocytoma which secreted predominantly norepinephrine is reported. A tumor at the posterior wall of the left atrium was demonstrated by computed tomographic and magnetic resonance imaging scan. Tumor blush arising from the left circumflex branch was visualized by coronary angiography. The tumor (4 x 3.5 x 2 cm) was resected with adherent atrial wall and the defect reconstructed with the patients own pericardium under general anesthesia with artificial cardiopulmonary bypass. His subsequent postoperative recovery was uneventful. At the time of discharge, 8 weeks after operation, his blood pressure and plasma norepinephrine remained normal. The value of magnetic resonance imaging scan for the topographic diagnosis of cardiac pheochromocytoma is emphasized.

Adult↗
PubMed1993

Identification and characterization of adenosine A1 receptor-cAMP system in human glomeruli.

Although adenosine is known to affect renal function through stimulating adenosine receptors, little is known about A1 receptors in human glomeruli. Thus, we attempted to identify the adenosine A1 receptor-cyclic AMP (cAMP) system in human glomeruli. Normal renal cortical tissues were obtained at nephrectomy of patients with renal cell carcinoma. Glomeruli were isolated using a graded sieving method or dissected manually under a stereomicroscope. Radioligand binding assay using 2-chloro-N-[3H] cyclopentyl adenosine ([3H]CCPA, an A1 agonist ligand) was performed at 30 degrees C for 90 minutes. Cyclic AMP (cAMP) produced in glomeruli was measured after incubation with different concentrations of N6-cyclohexyladenosine (CHA; A1 agonist) and a phosphodiesterase inhibitor. The specific binding was saturated within 60 minutes and reversible by adding 1 mM of theophylline. Scatchard plot analysis revealed a single class of binding site (Kd = 1.78 +/- 0.21 nM, Bmax = 271.7 +/- 35.8 fmol/mg protein). The specific binding was inhibited dose-dependently by various agents in an order suggesting A1 receptor specificity. CHA inhibited the production of cAMP in microdissected human glomeruli. This inhibitory effect was antagonized by 8-cyclopentyl-1,3-dipropylxanthine (DPCPX; A1 antagonist). This is the first study revealing the presence of the A1 receptor-cAMP system in human glomeruli using a radioligand binding assay method and by measuring the cAMP production.

Adenosine↗