Biomedical subjects

Hitonobu Tomoike

Publications and source records attributed to Hitonobu Tomoike.

98 records · Page 6Linked to original sources

PubMed2002

Verification of 525 coding SNPs in 179 hypertension candidate genes in the Japanese population: identification of 159 SNPs in 93 genes.

Single-nucleotide polymorphisms (SNPs) located in coding regions (coding SNPs; cSNPs) with amino acid substitution can potentially alter protein function. Therefore, identification of the nonsynonymous cSNPs of the genes of common diseases is valuable in tests of association with phenotypes. In this study, we validated 525 candidate cSNPs from 179 hypertension candidate genes deposited in the publicly available database dbSNP by DNA sequencing of samples from 32 Japanese individuals. We identified a total of 143 SNPs (27%) in 93 hypertension candidate genes. We also identified 16 new SNPs, for a total of 159 SNPs. Of the 159 SNPs thus identified, 104 were nonsynonymous. We estimate that approximately 20% of the SNPs deposited in dbSNP database showed a minor allele frequency of over 5%. The candidate SNPs for hypertension identified in this study would be valuable for association studies with hypertension to accelerate the identification of hypertension genes.

Gene Frequency↗

PubMed2002

Restitution properties and occurrence of ventricular arrhythmia in LQT2 type of long QT syndrome.

INTRODUCTION: The aim of this study was to clarify the ventricular tachyarrhythmia mechanism induced by the I(Kr)-blocking agent E4031, simulating the LQT2 form. Electrophysiologic properties were examined in 13 canines before and after administration of E4031. METHOD AND RESULTS: Thirty-six needle electrodes were inserted into the anterior left ventricular wall. From each needle, local unipolar electrograms were obtained from four intramural sites. Activation time (AT) and activation-recovery interval (ARI) were measured. To evaluate the susceptibility to ventricular arrhythmia, intramural ARI dispersions and the restitution relationship between ARI and diastolic interval were calculated. After E4031 administration, ARI prolonged uniformly in each myocardial layer. However, ARI dispersion was not augmented compared with control. The slope of the ARI restitution curve after E4031 was significantly steeper than control. A steep slope may result from augmented ARI alternans. In 11 of the 13 canines, ventricular tachyarrhythmia was induced by programmed stimulation after E4031, whereas no arrhythmia was induced by the same protocol in control. CONCLUSION: Steepness of electrical restitution may play a major role in arrhythmogenicity in LQT2 hearts.

Animals↗

PubMed2002

Inward rectifier K+ channel Kir2.3 is localized at the postsynaptic membrane of excitatory synapses.

Classical inwardly rectifying K+ channels (Kir2.0) are responsible for maintaining the resting membrane potential near the K+ equilibrium potential in various cells, including neurons. Although Kir2.3 is known to be expressed abundantly in the forebrain, its precise localization has not been identified. Using an antibody specific to Kir2.3, we examined the subcellular localization of Kir2.3 in mouse brain. Kir2.3 immunoreactivity was detected in a granular pattern in restricted areas of the brain, including the olfactory bulb (OB). Immunoelectron microscopy of the OB revealed that Kir2.3 immunoreactivity was specifically clustered on the postsynaptic membrane of asymmetric synapses between granule cells and mitral/tufted cells. The immunoprecipitants for Kir2.3 obtained from brain contained PSD-95 and chapsyn-110, PDZ domain-containing anchoring proteins. In vitro binding assay further revealed that the COOH-terminal end of Kir2.3 is responsible for the association with these anchoring proteins. Therefore, the Kir channel may be involved in formation of the resting membrane potential of the spines and, thus, would affect the response of N-methyl-D-aspartic acid receptor channels at the excitatory postsynaptic membrane.

Adaptor Proteins, Signal Transducing↗

PubMed2002

Regional prolongation of ARI and altered restitution properties cause ventricular arrhythmia in heart failure.

The mechanism of arrhythmogenicity in heart failure remains poorly understood. We examined the relationship between electrical abnormalities and ventricular arrhythmia by using experimental heart failure models. Sixty unipolar electrograms were recorded from the entire cardiac surface in control dogs (n = 13) and pacing-induced heart failure dogs (n = 16). In failing hearts, activation time (AT) was delayed at the apex, and AT dispersion increased in failing hearts. Activation-recovery intervals (ARI) were prolonged mainly at the apex and ARI dispersion was significantly augmented. The slope of the ARI restitution curve, interaction of diastolic interval, and ARI in failing hearts was significantly steeper than in control hearts. Ventricular fibrillation (VF) was easily induced by programmed stimulation in failing hearts, whereas no arrhythmia occurred in control hearts. Computer simulation studies could reproduce the experimental results. Altering the ARI restitution to the steep slope causes VF in a model heart. It is suggested that electrical remodeling, especially steepness of electrical restitution, may play a role in arrhythmogenicity in failing hearts.

Animals↗

PubMed2002

Comparison of nitric oxide production in response to carbachol between macrovascular and microvascular cardiac endothelial cells.

Cardiac microvascular endothelial cells (EC) play an important role in the physiological regulation of coronary blood flow, but their function has not been rigorously examined, because suitable in vitro models have not been available. Cardiac macrovascular and microvascular EC were isolated and cultured from 14-16-week-old Sprague-Dawley rats to examine the pharmacological responses of carbachol-induced nitric oxide (NO) production using a Griess method. Carbachol-induced NO production was only detected in cardiac macrovascular EC, which suggests that endothelial production of NO differs between macrovascular and microvascular EC. Next, cardiac microvascular EC was treated with either vehicle, angiotensin-converting enzyme (ACE) inhibitor (captopril, 10 micromol/L) or angiotensin II type 1 (AT1) receptor antagonist (CV11974, 10 micromol/L) for 4 days. Carbachol-induced NO production was improved by captopril (136+/-45nmol, p<0.01 vs vehicle) and CV11974 (146+/-30nmol, p<0.01 vs vehicle). Angiotensin II concentration in the culture medium and protein expressions of endothelial nitric oxide synthase and AT1 receptor in the EC were similar among the 3 groups. Interestingly, the level of muscarinic subtype 3 (M3) receptor was significantly increased in the EC treated with captopril (214%, p<0.01) and CV11974 (296%, p<0.01). When cardiac microvascular EC were treated with neomycin (non-selective phospholipase C inhibitor), carbachol-induced NO production was also improved (146+/-35nmol, p<0.01, neomycin I mmol/L) together with increased expression of M3 receptor (p<0.01). These data suggest that the upregulation of the M3 receptor by captopril or CV11974 occurs via a phospholipase C-dependent pathway. Cardiac microvascular EC also produced NO constitutively, as did the macrovascular EC, but carbachol-induced NO production was decreased. The present data suggest that the upregulation of the M3 receptor by the ACE inhibitor and AT1 receptor antagonist is a new beneficial effect of these drugs on microvascular endothelial function.

Angiotensin II↗

PubMed2002

Aldehyde dehydrogenase 2 gene is a risk factor for myocardial infarction in Japanese men.

In epidemiological studies, moderate alcohol consumption has been consistently associated with a reduced risk of myocardial infarction (MI). About half of Japanese show an extremely high sensitivity to alcohol (ethanol), which is due to a missense mutation from glutamic acid (Glu) to lysine (Lys) at codon 487 in an isoenzyme of aldehyde dehydrogenase (ALDH2) with a low Km. We obtained a preliminary result that subjects homozygous for the Lys 487 allele had higher risk for myocardial infarction. The purpose of the present study was to assess this hypothesis by employing a larger cohort of subjects with MI. The experimental group consisted of 342 male subjects with demonstrated MI who were selected randomly from our outpatient clinic. As controls, we employed 1,820 male subjects with no cardiovascular complications who were selected from the Suita Study. All subjects provided their written informed consent to participate in the genetic analyses. Subjects with MI were older and had higher body mass index, higher prevalence of diabetes mellitus, higher prevalence of smoking habit, higher prevalence of the Lys/Lys genotype (homozygous for Lys 487 allele), and lower high density lipoprotein (HDL) cholesterol level (HDL-C). The ALDH2 genotype affected the level of alcohol consumption, and HDL-C. Multiple logistic analyses indicated that the odds ratio of the Lys/Lys genotype to the Lys/Glu+Glu/Glu genotype was 1.56 (p=0.0359). Inclusion of HDL-C as one of the independent variables downplayed the importance of the ALDH2 genotype. This may indicate that the ALDH2 genotype affects MI via its effects on HDL-C. In conclusion, the ALDH2 Lys/Lys genotype is a risk factor for myocardial infarction in Japanese men due to its influence on HDL cholesterol level.

Alcohol Drinking↗

PubMed2002

A single-nucleotide polymorphism in C-type natriuretic peptide gene may be associated with hypertension.

We conducted an association study between genetic variants of C-type natriuretic peptide gene (CNP) and hypertension in a Japanese population. We found four genetic variants, two in the promoter region, one missense mutation, and one in the 3'-untranslated region (3'-UTR), and genotyped all four variants in 2,006 subjects recruited from the Suita study. One of the variants, G2628A in 3'-UTR, was found to be associated with blood pressure. Multiple logistic analyses indicated that the genotype of the G2628A polymorphism (GG=1, GA+AA=2) (p=0.0034), sex (p=0.0288), alcohol consumption (p=0.0002), age (p<0.0001), and body mass index (p<0.0001) were predictors of hypertension. The odds ratio of the GA+AA genotype over the GG genotype for hypertension was 1.40 (p=0.0034, 95% confidence interval (CI) 1.12-1.75). Multiple logistic analyses in a younger subpopulation aged below 65 years indicated that the odds ratio of the GA+AA genotype over the GG genotype for hypertension was 1.58 (p=0.0024, 95%CI 1.18-2.12). Thus, the CNP G2628A polymorphism made an even greater contribution to hypertension in the younger subpopulation.

Age Distribution↗

PubMed2002

The Na+-Ca2+ exchanger contributes to beta-adrenoceptor mediated positive inotropy in mouse heart.

The L-type Ca2+ current (I(Ca,L)) plays an important role in the regulation of cardiac contractility. However, there is little data with regard to the significance of the I(Ca,L)-independent mechanism of beta-adrenoceptor mediated positive inotropy. The effects of isoproterenol (ISO) on I(Ca,L) and contractility in the presence of Ca2+ channel blockers (nifedipine, verapamil) were examined in adult mouse ventricular myocytes. ISO increased contractility over the level before the administration of Ca2+ channel blocker, although it had a very limited effect on I(Ca,L). The positive inotropy of ISO disappeared after administration of Ni2+, an inhibitor of the Na+-Ca2+ exchanger. The addition of ISO after nifedipine pretreatment also increased the [Ca2+]i transient over the control level and the application of Ni2+ or KB-R7943, a selective Na+-Ca2+ exchange inhibitor (reverse mode), abolished the increase in [Ca2+]i transient. Therefore, an I(Ca,L)-independent mechanism plays a significant role in beta-adrenoceptor mediated positive inotropy. The Na+-Ca2+ exchanger is necessary for the development of this action.

Animals↗