Biomedical subjects

S Ishiwata

Publications and source records attributed to S Ishiwata.

At least 55 records · Page 3Linked to original sources

PubMed1998

Regulatory roles of MgADP and calcium in tension development of skinned cardiac muscle.

We investigated the regulatory roles of MgADP and free Ca2+ in isometric tension development in skinned bovine cardiac muscle. We found that, in the relaxed state without free Ca2+, MgADP elicited a sigmoidal increase in active tension, as is the case in skeletal muscle (ADP-contraction). The critical MgADP concentration, at which the tension increment became half-maximal, increased in proportion to MgATP concentration, with a slope of approximately 1 for cardiac and 4 for skeletal muscle. Raising the free Ca2+ concentration decreased the critical MgADP concentration in proportion to the free Ca2+ concentration. In addition, the apparent Ca2+ sensitivity of tension development increased with MgADP, while decreasing with inorganic phosphate (Pi); MgADP suppressed the Ca(2+)-desensitizing effect of Pi in a concentration-dependent manner. These activating effects of MgADP were quantitatively assessed by means of a model based upon the kinetic scheme of actomyosin ATPase. These experimental results and model simulation suggest that the state of thin filaments is synergistically regulated by both the binding of Ca2+ to troponin and the formation of the actomyosin-ADP complex.

Actomyosin↗

PubMed1998

Long-term outcome in triple-vessel coronary artery disease in medically treated Japanese patients.

The long-term outcome in 198 patients with triple-vessel disease (TVD) treated medically was investigated. The patients, who underwent coronary angiography between September 1973 and February 1984, had significant (75% or more) stenotic lesions in all three major coronary arteries. The mean follow-up period was 8.4 years. The 5- and 10-year survival rates were 80.7% and 64.2%, respectively. Cardiac death occurred in 73 patients (36.9%) and nonfatal cardiac events developed in 60 patients (30.9%) during follow-up. When cardiac death and nonfatal myocardial infarction (MI) were defined as cardiac events, the annual attrition rate was 4.7%. There was no difference in survival with regard to the presence or absence of MI, the site of infarction, or the presence of total occlusion. In the AP group, however, the survival rate decreased as the number of totally-occluded arteries increased. In the MI group, the survival rate was not altered by the number of totally-occluded arteries, but was affected by the ejection fraction (EF). The 5-year survival rate was better in patients with good left ventricular function (EF > or = 60%) than in those with impaired left ventricular function (EF < 60%), although the 10-year survival rate was similarly low in both groups. Revascularization such as PTCA or CABG might improve the long-term outcome in patients with TVD.

Angina Pectoris↗

PubMed1998

[Relationship between evolution of ischemic heart disease and changes in lipid profile].

The relationship between the evolution of ischemic heart disease and changes in lipid profile was investigated in 115 of 11,875 patients underwent coronary angiography (CAG). The 115 patients had no significant stenosis on initial CAG and underwent repeat CAG for several reasons. Changes in lipid profile and other coronary risk factors were compared in 30 patients who developed ischemic cardiac events (Group E) and 85 patients who did not (Group NE). Ischemic cardiac events were defined as ischemic chest symptoms with ST-T changes or appearance of significant angiographic stenosis. At initial CAG, smoking was significantly more common in Group E (23.3% vs 4.7%, p < 0.01) and high-density lipoprotein cholesterol was significantly lower in Group E (42 +/- 11 vs 48 +/- 15 mg/dl, p < 0.05). At repeat CAG, smoking continued to be significantly more common in Group E (26.7% vs 10.6%, p < 0.05), and serum cholesterol (219 +/- 36 vs 193 +/- 34 mg/dl, p < 0.01) and low-density lipoprotein cholesterol (141 +/- 33 vs 115 +/- 29 mg/dl, p < 0.01) were also significantly higher in Group E. Multivariate analysis revealed only the increase of serum cholesterol at repeat CAG was a significant factor in the evolution of coronary artery disease (p = 0.026). Two patients from Group E died of cardiac causes within 1 year after repeat CAG but no patients in Group NE died (6.7% vs 0%, p < 0.05). Increased serum cholesterol level is related to the evolution of ischemic heart disease and cardiac death.

Cholesterol↗

PubMed1997

Redifferentiation of smooth muscle cells after coronary angioplasty determined via myosin heavy chain expression.

BACKGROUND: The pathophysiology of phenotypic modulation of smooth muscle cells (SMCs) involved in restenosis after angioplasty is not well understood. Smooth muscle myosin heavy chain (SM MHC) isoforms (SM1 and SM2) are specific markers for SMC differentiation. In particular, SM2 is useful as a marker of mature SMCs. SMemb is a nonmuscle myosin heavy chain (NM MHC) whose expression is upregulated in immature or activated SMC. METHODS AND RESULTS: To determine SMC phenotypes in neointimal tissues after percutaneous transluminal coronary angioplasty (PTCA), we performed immunohistochemistry on human coronary arteries with antibodies against alpha-SM actin, SM1, SM2, and SMemb. Tissues were obtained from six autopsied patients and from atherectomy specimens from 16 patients who had undergone PTCA. Medial SMCs were positive for alpha-actin, SM1, and SM2. Expression of SM1 and SM2 in the neointima varied with the time after intervention, whereas alpha-actin was constitutively expressed in all cases studied. Neointimal cells at 16 and 20 days after PTCA contained alpha-actin but little or no SM1 or SM2, indicating that these cells modulated their phenotype to the immature state. Neointimal SMCs recovered SM MHC expression, first SM1 and then SM2, by 6 months after PTCA. Increased expression of SMemb was found in the neointima but without apparent relationship to the time after PTCA. CONCLUSIONS: Neointimal SMCs show features of an undifferentiated state, indicated by altered expression of SM MHC, and undergo redifferentiation in a time-dependent manner. The expression of SM MHC isoforms provides insight into the biology of healing after angioplasty and furnishes useful tools for the understanding of the roles of differentiation and phenotypic modulation of SMCs in human vascular lesions.

Aged↗

PubMed1997

Axial rotation of sliding actin filaments revealed by single-fluorophore imaging.

In the actomyosin motor, myosin slides along an actin filament that has a helical structure with a pitch of approximately 72 nm. Whether myosin precisely follows this helical track is an unanswered question bearing directly on the motor mechanism. Here, axial rotation of actin filaments sliding over myosin molecules fixed on a glass surface was visualized through fluorescence polarization imaging of individual tetramethylrhodamine fluorophores sparsely bound to the filaments. The filaments underwent one revolution per sliding distance of approximately 1 microm, which is much greater than the 72 nm pitch. Thus, myosin does not "walk" on the helical array of actin protomers; rather it "runs," skipping many protomers. Possible mechanisms involving sequential interaction of myosin with successive actin protomers are ruled out at least for the preparation described here in which the actin filaments ran rather slowly compared with other in vitro systems. The result also indicates that each "kick" of myosin is primarily along the axis of the actin filament. The successful, real-time observation of the changes in the orientation of a single fluorophore opens the possibility of detecting a conformational change(s) of a single protein molecule at the moment it functions.

Actins↗

PubMed1997

Mechanical efficiency in hypertrophic cardiomyopathy assessed by positron emission tomography with carbon 11 acetate.

This study was performed to assess the relation between the regional work and oxidative metabolism in hypertrophic cardiomyopathy (HCM). By using carbon 11 acetate as a tracer of myocardial blood flow (%A(0)) and oxygen consumption (k value), 12 patients with HCM with asymmetric septal hypertrophy and 10 normal subjects were studied. Regional work rate (RWR) of the left ventricle was estimated by wall stress and wall thickness. %A(0) in hypertrophied septum was similar to that in nonhypertrophied free wall (92.6% +/- 2.8% vs 93.5% +/- 3.8%; p = not significant). However, oxygen consumption was significantly lower in hypertrophied septum than in nonhypertrophied free wall (0.043 +/- 0.011 vs 0.057 +/- 0.013 min(-1); p < 0.001). The k value in nonhypertrophied free wall was similar to the value observed in normal subjects (0.062 +/- 0.013). Average values for RWR in hypertrophied septum, nonhypertrophied free wall, and normal subjects were 0.26 +/- 0.07,0.62 +/- 0.02,and 1.98 +/- 0.15 J/cm3/ min, respectively. Furthermore, the analysis of covariance, in which the effect of RWR was removed as a covariate, revealed that the overall RWR-corrected k value was much larger in patients with HCM (0.109 vs 0.062, p < 0.0001) than expected from the decreased regional myocardial work, suggesting that there was a diffused inefficiency in oxygen consumption. We concluded, therefore, that the relative value of oxidative metabolism in patients with HCM is significantly higher than that of the normal subjects, suggesting the presence of reduced mechanical efficiency.

Acetates↗

PubMed1997

Postangioplasty restenosis: platelet activation and the coagulation-fibrinolysis system as possible factors in the pathogenesis of restenosis.

We investigated the relationship between changes in hemostatic factors and postangioplasty restenosis by evaluating plasma levels of P-selectin, beta-thromboglobulin (BTG), and other markers of the coagulation-fibrinolysis system. Seventy-three consecutive patients (56 men and 17 women) undergoing elective percutaneous transluminal coronary angioplasty (PTCA) were enrolled in this study. Patients with acute myocardial infarction within the previous month, unstable angina pectoris, chronic total occlusion, target lesions involving saphenous vein grafts, or coronary artery bypass grafting within the previous 6 months were excluded. Fasting blood samples were obtained before elective PTCA and at follow-up coronary angiography. In patients with restenosis, plasminogen activator inhibitor type-1 (PAI-1) levels were significantly higher (88.2 +/- 36.1 vs 118.5 +/- 50.0 ng/dl; p< 0.05) and plasmin-plasmin inhibitor complex (PIC) levels were significantly lower (0.76 +/- 0.26 vs 0.61 +/- 0.26 microg/ml; p < 0.02) than at baseline. P-Selectin levels were also significantly higher (192 +/- 68 vs 239 +/- 99 ng/ dl; p<0.01) and a positive correlation existed between P-selectin and BTG levels (r= 0.43; p< 0.05). The higher PAI-1 and lower PIC levels in patients with postangioplasty restenosis suggest that impaired fibrinolysis may play a role in the pathogenesis of restenosis, whereas the positive correlation between P-selectin and BTG levels implies a role for activated platelets in restenosis.

Angioplasty, Balloon, Coronary↗

PubMed1997

Interhead distances in myosin attached to F-actin estimated by fluorescence energy transfer spectroscopy.

Fluorescence resonance energy transfer (FRET) spectroscopy has been used to determine distances between probes attached to the most reactive sulfhydryl (SH1) group on individual myosin "heads." We measured intramolecular and intermolecular interhead distances as well as the distance between one head of heavy meromyosin (HMM) mixed with subfragment-1 (S1) heads attached to F-actin under rigor conditions. The SH1 cysteine was specifically labeled with either a donor (5-((((2-iodoacetyl)amino)ethyl)amino)naphthalene-1-sulfonic acid) or an acceptor probe (5-iodoacetamidofluorescein). In free solution, the distance between these probes was too large to allow significant FRET, but in the rigor complex with F-actin, intermolecular interhead distances between S1 molecules, HMM molecules, or S1 and HMM were determined to be 6.0-6.3 nm. The radial coordinate of the labels relative to F-actin was 5.0-6.4 nm. However, the intramolecular interhead distance in HMMs in which the two heads were labeled with D and A probes was estimated to be larger. The binding affinity of the second head of HMM(D/A) to F-actin may be reduced because of heterogeneous modification of the SH1 groups, such that the probability of single-head binding is increased.

Actins↗

PubMed1997

Two-dimensional arrangement of a functional protein by cysteine-gold interaction: enzyme activity and characterization of a protein monolayer on a gold substrate.

We have characterized the functional protein, myosin subfragment 1 (S1), attached to a gold substrate by the sulfhydryl groups of cysteine in proteins. The amino groups of the regulatory light chain (RLC) isolated from myosin were labeled with a radioisotope (125I), and the labeled RLC was incorporated into S1 from which the RLC had been removed. The radiation from 125I showed that S1 molecules had attached to the gold and, through the interference effect of the monochromatic radiation from 125I, provided information about the position of labeled RLC sites in the S1 monolayer. The interference fringes showed that the RLC was located close to the gold surface and that all of the adsorbed S1 molecules had the same orientation. We confirmed that the motor function of S1 on the gold surface is maintained by observing sliding movement at low ionic strength and by observing the detachment at high ionic strength of fluorescent actin filaments in the presence of ATP. We also found that the adsorbed S1 molecules were not removed from the Au surface by a reducing agent. Thus the Au-S bond is more stable than the S-S bond.

Actins↗

PubMed1997

Effects of haloperidol and cocaine pretreatments on brain distribution and kinetics of [11C]methamphetamine in methamphetamine sensitized dog: application of PET to drug pharmacokinetic study.

Repeated administration of methamphetamine (MAP) causes behavioral sensitization in animals. We previously reported that the maximum accumulation level of [11C]MAP in the MAP-sensitized dog brain was 1.4 times higher than that in the control. In behavioral studies, haloperidol (a dopamine D2 receptor antagonist) prevents MAP-induced behavioral sensitization, and cocaine (a dopamine reuptake blocker) has the cross-behavioral sensitization with MAP. In the present study, to elucidate the relation between the MAP-induced behavioral sensitization and the pharmacokinetics of MAP, we investigated the effects of haloperidol and cocaine pretreatments on brain regional distribution and kinetics of [11C]MAP using positron emission tomography (PET). A significant increase of [11C]MAP uptake into the sensitized dog brain was prevented by haloperidol and cocaine pretreatments. These pharmacokinetic changes were not due to the changes in the rate of MAP metabolism. These results suggest haloperidol and cocaine can change the cerebral pharmacokinetic profile of MAP in the behavioral-sensitized dog. The variations of MAP-accumulation may affect the development or expression of MAP-induced behavioral sensitization.

Animals↗

PubMed1997

Determination of ascorbic acid in human vitreous humor by high-performance liquid chromatography with UV detection.

PURPOSE: Ascorbic acid (AA) accumulates in vitreous at a concentration several times higher than in plasma. It has been suggested that AA may serve as an antioxidant that protects ocular tissues from free radical attack. There are many reports about the concentration of AA in ocular tissues. However, AA in adult human vitreous humor has not been determined. We measured concentrations of AA from pathologic human vitreous samples and compared the results. METHODS: AA was measured by high-performance liquid chromatography (HPLC) with UV detection. Human vitreous humor was collected from patients undergoing pars plana vitrectomy. RESULTS: AA was quantified in vitreous humor of proliferative diabetic retinopathy (PDR), proliferative vitreoretinopathy (PVR), macular hole (MH), idiopathic premacular fibrosis (PMF), and Terson syndrome (Terson). The concentrations of AA were 120.9 +/- 36.3 micrograms/ml (mean +/- SD), 129.8 +/- 36.6, 311.5 +/- 126.7, 446.9 +/- 154.2 and 406.0 +/- 22.0, respectively. There was no significant difference between the PDR and the PVR groups (unpaired t-test). Patients with PDR and PVR showed significantly lower concentrations of AA than those with MH, PMF, and Terson (p < 0.01). CONCLUSIONS: These findings suggest that increased oxidative stress may be produced in the ocular tissues of eyes with PDR and PVR, and AA appears to be consumed (oxidized) in performing its protective role.

Ascorbic Acid↗

PubMed1997

Alteration of DNA methylation levels in MRL lupus mice.

Recent reports suggest that DNA methylation is involved in the cause of autoimmune disease. We investigated the alteration of DNA methylation levels in lupus strains of mice, MRL/lpr as a model, which develop an age-dependent lymphadenopathy and autoimmune disease. DNA methylation levels of thymus and axillary lymph nodes in 20-week-old MRL/lpr mice, which are in an autoimmune disease state, were lower than those of 4-week-old MRL/lpr mice with no symptoms as yet. No significant changes were observed in MRL/+ strain mice, which seemed normal at least 20 weeks, while DNA methylation levels in the spleen of both strains of mice increased significantly from the age of 4 to 20 weeks. However, no significant changes of DNA methylation levels in peripheral blood were observed with ageing in MRL strains. Moreover, we clarified that administration of 5-azacytidine had a strong effect on longer survival of MRL/lpr mice and reduced DNA methylation levels in the axillary lymph nodes and spleen. The possible relevance of DNA methylation levels to the progression of autoimmune disease is discussed.

Animals↗

PubMed1997

Myocardial blood flow and metabolism in patients with hypertrophic cardiomyopathy--a study with carbon-11 acetate and positron emission tomography.

The underlying pathophysiology of hypertrophic cardiomyopathy (HCM) is still unclear. positron emission tomography is a suitable and promising technique for the detection of possible metabolic consequences of the disease. To assess regional myocardial blood flow and metabolism, 19 asymptomatic or only mildly symptomatic patients with HCM and 10 normal control subjects were studied using carbon-11 acetate and fluorine-18-labelled deoxyglucose (FDG) as tracers of myocardial blood flow (Ao), oxygen consumption (k), and exogenous glucose utilization. In the patients, regional Ao in the hypertrophied septum and apex (H) was similar to that in the nonhypertrophied free wall (N) (91.3 +/- 3.9% vs 92.9 +/- 3.1%; p = NS). However, the k values were significantly lower in H than in N (0.044 +/- 0.012 vs 0.060 +/- 0.016/min, p < 0.0001). The k value in N and normal control subjects (0.062 +/- 0.013) was similar. Postprandial FDG uptake was lower in H than in N (70 +/- 16 vs 91 +/- 7%; p < 0.0001) in 16 patients and slightly higher in 3 patients. Fasting FDG study showed increased FDG uptake in H in 3 out of 13 patients, suggesting a disorder of the myocardial microvascular circulation. A relative decrease in hypertrophied septal and apical oxidative metabolism and glucose utilization without any corresponding perfusion defect could reflect abnormal regional aerobic metabolism in the disproportionately thickened myocardium in patients with HCM. This suggests that a primary myocardial metabolic defect might be present in patients with HCM.

Adolescent↗

PubMed1997

Long-term outcome in double-vessel coronary artery disease in Japanese patients.

The long-term (average: 10 years) outcome in 220 patients with double-vessel disease (DVD) treated medically was investigated. The patients underwent coronary angiography between September 1973 and February 1984, and significant (75% or more) stenosis was detected in each of two major coronary arteries. These patients showed relatively good 5-year and 10-year survival rates of 94.5% and 87.4%, respectively. Cardiac death occurred in 31 patients (14.1%) and nonfatal myocardial infarction (MI) developed in 16 patients (7.3%) during follow-up. When these were defined as cardiac events, the annual attrition rate was 3.1%. A comparison of the outcome with regard to the presence or absence of MI revealed worse results for the MI group, but no difference was observed between different sites of infarction. There was also no difference in outcome with regard to the presence or absence of lesions in the left anterior descending artery (LAD). In the MI group, patients with impaired left ventricular function (ejection fraction < or = 40%) had inferior survival to those with good left ventricular function. Thus, DVD associated with good left ventricular function had a relatively good outcome when treated medically, while patients with impaired left ventricular function might benefit from revascularization.

Angioplasty, Balloon, Coronary↗

PubMed1997

[Clinical analysis of infective endocarditis with aneurysmal formation of the mitral or aortic valve].

Echocardiographic findings, clinical features, and pathophysiology of mitral and aortic valve aneurysms were evaluated in four patients with pathologically proven aneurysms of the mitral and/or aortic valves associated with infective endocarditis. These four were selected from 20 patients hospitalized in our institute from April 1990 to May 1995 because of infective endocarditis. All four patients had received repeated, inadequate antibiotic treatments at other medical institutions prior to admission, and underwent surgical repair because of acute hemodynamic exacerbation associated with aneurysmal perforation. Six aneurysms (three mitral and three aortic valve aneurysms) were detected before surgery, including two by transthoracic echocardiography and four by transesophageal echocardiography. The echocardiographic findings typical of aortic valve aneurysm were: ringed echo at the level of the aortic annulus in the short-axis view; turbulent flow within the ringed echo; and dome formation of the aortic valve that persisted throughout the cardiac cycle. All mitral valve aneurysms were true aneurysms without active inflammatory changes or significant destructive lesions, and were associated with severe infective aortic regurgitation. Histologic examination of the aortic valve in these patients showed active inflammation and extensive destruction, suggesting that these valves were the primary focus of infection. One patient had an aortic valve aneurysm without apparent mitral involvement, indicating that another mechanism had mediated aneurysmal formation. We conclude that: diagnosis of mitral or aortic valve aneurysms in patients with infective endocarditis has important therapeutic implications, and therefore, transesophageal echocardiographic examination should be done in such patients: there are three key echocardiographically diagnostic findings of aortic valve aneurysm as mentioned above; and several unknown factors may contribute to aneurysmal formation of the mitral or aortic valve in patients with infective endocarditis.

Adult↗

PubMed1996

Ca(2+)-induced tension development in the stalks of glycerinated Vorticella convallaria.

We have developed a method of measuring the isometric tension in glycerinated stalks of Vorticella convallaria. Using this method, we measured tension vs. pCa relations in glycerinated V. convallaria stalks. The maximum isometric tension was 4 x 10(-8) N on average. The Hill's parameter, n, which is the number of calcium ions bound simultaneously and cooperatively to a contractile element (a force generating element), is approximately 3.2 when the Ca2+ concentration is increased and 2.5 when it is decreased. In order to estimate the efficiency of the energy conversion of Ca2+ binding to mechanical work, we measured the Ca(2+)-induced Carnot cycle in the Vorticella stalk. The energy efficiency was tentatively estimated to be about 7%. With this method, we have also succeeded in measuring the isometric tension of isolated spasmoneme, the rubber-like contractile fibrous organelle in the stalk. The maximum tension of spasmoneme was approximately one tenth that of the glycerinated stalk. We speculate that the isolated spasmoneme was only partially functional due to damage sustained when it was pulled out of the stalk.

Animals↗

PubMed1996

Structural and functional reconstitution of thin filaments in the contractile apparatus of cardiac muscle.

The muscle contractile apparatus has a highly ordered liquid crystalline structure. The molecular mechanism underlying the formation of this apparatus remains, however, to be elucidated. Selective removal and reconstitution of the components are useful means of examining this mechanism. In addition, this approach is a powerful technique for examining the structure and function of a specific component of the contractile system. In this study we have achieved the structural and functional reconstitution of thin filaments in the cardiac contractile apparatus. First, all thin filaments other than short fragments at the Z line were removed by treatment with gelsolin. Under these conditions no active tension could be generated. By incorporating exogenous actin into these thin filament-free fibers, actin filaments were reconstituted, and active tension, which was insensitive to Ca2+, was restored. The active tension after the reconstitution of thin filaments reached 135 +/- 64% of the original level. The augmentation of tension was attributable to the elongation of reconstituted filaments. As another possibility for augmented tension generation, we suggest the presence of an inhibitory system that was not reconstituted. In any case, the thin filaments of the cardiac contractile apparatus are considered to be assembled so as not to develop the highest degree of tension. Incorporation of the tropomyosin-troponin complex fully restored Ca2+ sensitivity without affecting maximum tension. The present results indicate that a muscle contractile apparatus with a higher order structure and function can be constructed by the self-assembly of constituent proteins.

Actins↗

PubMed1996

Preparation of bead-tailed actin filaments: estimation of the torque produced by the sliding force in an in vitro motility assay.

By coating covalently the surface of a polystyrene bead (diameter = 1 micron) with gelsolin, we have succeeded in attaching the bead selectively at the barbed end of an actin filament and forming a 1:1 bead-actin filament complex. On a layer of heavy meromyosin on a nitrocellulose-coated coverglass, this bead-actin filament complex slid smoothly, trailing the bead at its end. Therefore we called this preparation "bead-tailed" actin filaments. The sliding velocity was indistinguishable from that of nonbeaded filaments. With use of this system, we tried to detect the axial rotation (rotation around the filament axis) in a sliding actin filament. Although a single bead at the tail end did not serve as the marker for the axial rotation, we occasionally found another bead bound to the tail bead. In this case, the orientation of the bead-aggregate could be followed continuously with a video monitor while the filament was sliding over heavy meromyosin. We observed that actin filaments slid over distances of many tens of micrometers without showing a complete turn of the bead-aggregates. On the basis of the calculation of rotational friction drag on the bead-aggregate, we estimate that the rotational component of the sliding force and the torque produced on a sliding actin filament (length < or = 10 microns) did not accumulate > 1 pN and 5 pN.nm, respectively. In the present system of randomly oriented heavy meromyosin lying on a nitrocellulose film without an external load.

Actins↗