Biomedical subjects

M Yamaki

Publications and source records attributed to M Yamaki.

At least 19 recordsLinked to original sources

PubMed1992

Isozymes of cyclic-3',5'-nucleotide phosphodiesterases in renal epithelial LLC-PK1 cells.

Metabolism of cAMP and cGMP by the major types (families) of cyclic-3',5'-nucleotide phosphodiesterases (PDE) was studied in confluent renal epithelial LLC-PK1 cells grown in vitro. LLC-PK1 cells mainly contain the cAMP-specific rolipram-sensitive PDE type-IV (PDE-IV), the Ca(2+)-calmodulin dependent PDE type-I and cGMP-specific PDE type-V; all these PDEs are mainly localized in cytosol. Analysis of PDE activities in soluble extract of LLC-PK1 cell homogenate by FPLC ionex chromatography on Mono-Q column also disclosed the presence of low activities of cGMP-stimulated PDE-II and PDE-III. Moreover, activity of PDE-IV was resolved into four distinct chromatographic peaks. The increase of cAMP level in response to incubation of intact LLC-PK1 cells with vasopressin (AVP) was markedly enhanced in the presence of rolipram, but not in the presence of other PDE isozyme-specific inhibitors. Incubation with AVP and atriopeptin (ANP) together resulted in increase in cGMP and a small decrease of cAMP accumulation in LLC-PK1 cells. Results of these studies first show that the LLC-PK1 cells contain all five major types of PDE isozymes where PDE-IV, PDE-I and PDE-V are quantitatively predominant. The rolipram-sensitive PDE-IV, present in several chromatographically distinct forms, appears to be the key PDE isozyme involved in control of cAMP generated in response to stimulation by AVP in LLC-PK1 cells.

3',5'-Cyclic-AMP Phosphodiesterases↗

PubMed1992

Characterization of inorganic fillers in visible-light-cured dental composite resins.

Inorganic fillers in seven visible-light (VL)-cured dental composite resins were examined for their size, composition, phase and content, employing the following analytical instruments. SEM observations indicated that five samples could be classified into the hybrid type while the remaining two belonged to micro-filled and sub-micron types. EDX analyses revealed that five samples contained BaO while others lacked BaO. XRD analyses showed that three were in vitreous phase, two were in the crystalline phase and two were mixtures of both. DTG thermal analyses indicated that the hybrid type composites had the higher inorganic filler content (wt%) than the composites of two other types. In conclusion, wide varieties exist in the inorganic fillers in VL-cured dental composite resins currently utilized.

Aluminum Oxide↗

PubMed1992

In-vitro and in-vivo wear profile of composite resins.

The aim of this study was to evaluate in-vitro wear by two types of slurry of 10 commercial composite resin materials (seven hybrid and three microfilled composites). There was great variation in the in-vitro wear pattern by two types of slurry. The wear rate of microfilled composites was greater than that of hybrid composites, and a negative correlation was observed between wear rate and Knoop hardness values among all materials when hydroxyapatite slurry was used. In contrast, the wear rate of hybrid composites was greater than that of microfilled composites when abraded by green carborundum slurry. These abraded surfaces were compared with SEM micrographs of in-vivo composites surface after 4 years of service. The profile of in-vivo wear surfaces was found to be similar to that of in-vitro wear surfaces abraded with hydroxyapatite slurry.

Composite Resins↗

PubMed1992

Cyclic 3',5'-nucleotide diesterases in dynamics of cAMP and cGMP in rat collecting duct cells.

We studied cyclic 3',5'-nucleotide phosphodiesterase (PDE) isozymes and their role in adenosine 3',5'-cyclic monophosphate (cAMP) and cGMP metabolism in a rat inner medullary collecting duct (IMCD) cell line. The homogenized and fractionated IMCD cells of cAMP-PDE and all of cGMP-PDE activity were found in the cytosol. The majority of cytosolic cAMP-PDE (greater than 50%) was isozyme PDE-IV; the Ca(2+)-calmodulin-sensitive PDE-I was present only in cytosol. Preincubation of IMCD cells with PDE-IV inhibitor rolipram markedly (5x) enhanced levels of cAMP both basal and in the presence of [Arg8]vasopressin (AVP). Cilostamide (for PDE-III) or vinpocetine had no effect, whereas PDE-I inhibitor 8-methoxymethyl-3-isobutyl-1-methylxanthine (8-MeoM-IBMX) enhanced AVP-dependent cAMP levels. Exposure of IMCD cells to 2 microM ionomycin decreased both basal and AVP-stimulated cAMP. Depletion of Ca2+ by preincubation of IMCD cells in the Ca(2+)-free medium with ethylene glycol-bis (beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid markedly enhanced the stimulatory response of cAMP to AVP, and addition of 8-MeoM-IBMX further enhanced the AVP response. The levels of cGMP, basal or in response to atriopeptin (ANP), were not affected by PDE-V inhibitor zaprinast, but both inhibitors of PDE-I, 8-MeoM-IBMX and vinpocetine, increased basal cGMP, and 8-MeoM-IBMX also increased cGMP levels enhanced by ANP. The depletion of Ca2+ from IMCD cells alone had no effect on cGMP levels, but effects of 8-MeoM-IBMX and vinpocetine on the ANP-stimulated cGMP levels were enhanced.(ABSTRACT TRUNCATED AT 250 WORDS)

2',3'-Cyclic-Nucleotide Phosphodiesterases↗

PubMed1992

Localization of mRNAs coding for isozymes of plasma membrane Ca(2+)-ATPase pump in rat kidney.

We have studied localization of mRNAs coding isozymes of rat plasma membrane Ca(2+)-adenosinetriphosphatase pump (rPMCA) in the rat kidney, with use of reverse transcription (RT) with subsequent amplification by polymerase chain reaction (PCR). When zones of the kidney were separated by macrodissection, a large amount of mRNA coding isozyme rPMCA1 was found in all zones; mRNA for isozyme rPMCA2 was abundant in cortex and in outer medulla, and mRNA for isozyme rPMCA3 was prominent in outer medulla. The mRNAs were analyzed in microdissected cortical nephron segments by use of RT-PCR approach described previously [T. Moriyama, H. R. Murphy, B. M. Martin, and A. Garcia-Perez. Am. J. Physiol. 258 (Renal Fluid Electrolyte Physiol. 27): F1470-F1474, 1990]. We detected mRNA for isozyme rPMCA2 in microdissected distal convoluted tubules (DCT) and in cortical thick ascending limbs (CTAL) and, less consistently, also in proximal convoluted tubule and in glomeruli. The mRNA for isozyme rPMCA1 was abundant in glomeruli but was absent in all examined cortical tubular segments. Our results document that mRNAs for all three major isozymes of rPMCA are present and show a unique distribution in the three major zones of rat renal parenchyma. Specific mRNA coding for rPMCA2 was detected in cortical tubules, namely in CTAL and DCT, whereas mRNA coding isozyme rPMCA1 was found in glomeruli. We suggest that isozyme rPMCA2 might be specifically related to epithelial cells and their function, whereas rPMCA1 is probably a component of nonepithelial cells including these in glomeruli.

Animals↗

PubMed1992

Relation between recovery sequence estimated from body surface potentials and T wave shape in patients with negative T waves and normal subjects.

BACKGROUND: Advances in analytical methods of the epicardial electrical potentials allowed us to demonstrate spatial distributions of local recovery. Because local recovery will be reflected in events on body surface ECG mapping, abnormalities in recovery sequence that may be responsible for the origin of negative T waves can be detected from body surface potentials. METHODS AND RESULTS: Eighty-seven unipolar ECGs were recorded simultaneously from the entire thorax in patients having negative T waves on left anterior precordial leads and in normal subjects. These included 40 patients with anterior myocardial infarction (MI), 21 patients with left ventricular hypertrophy (LVH), and 44 male volunteers. We measured Tmax time, defined as the instant of maximal first derivative of the T wave as the index of local recovery (Wyatt's method). Parameters related to T wave potentials were positive T wave amplitude, negative T wave amplitude, and T integral. Significant correlations were observed between the Tmax time and each of the T wave potentials. The T wave potentials were dependent on Tmax times. In the anterior MI, the late Tmax times were located on the upper left anterior chest and early Tmax times on the lower right lateral chest. In the LVH, the area showing a delayed recovery was displaced in a left downward direction compared with anterior MI. CONCLUSIONS: Body surface Tmax time distributions clearly separate two negative T wave groups, i.e., anterior MI and LVH. Appearance of the negative T waves correlates well with the presence of the area with delayed Tmax time on the spatial distribution.

Adult↗

PubMed1992

Spectral analysis of 87-lead body surface signal-averaged ECGs in patients with previous anterior myocardial infarction as a marker of ventricular tachycardia.

BACKGROUND: There were few studies on the relation between the body surface distribution of high- and low-frequency components within the QRS complex and ventricular tachycardia (VT). METHODS AND RESULTS: Eighty-seven signal-averaged ECGs were obtained from 30 normal subjects (N group) and 30 patients with previous anterior myocardial infarction (MI) with VT (MI-VT[+] group, n = 10) or without VT (MI-VT[-] group, n = 20). The onset and offset of the QRS complex were determined from 87-lead root mean square values computed from the averaged (but not filtered) ECG waveforms. Fast Fourier transform analysis was performed on signal-averaged ECG. The resulting Fourier coefficients were attenuated by use of the transfer function, and then inverse transform was done with five frequency ranges (0-25, 25-40, 40-80, 80-150, and 150-250 Hz). From the QRS onset to the QRS offset, the time integration of the absolute value of reconstructed waveforms was calculated for each of the five frequency ranges. The body surface distributions of these areas were expressed as QRS area maps. The maximal values of QRS area maps were compared among the three groups. In the frequency ranges of 0-25 and 150-250 Hz, there were no significant differences in the maximal values among these three groups. Both MI groups had significantly smaller maximal values of QRS area maps in the frequency ranges of 25-40 and 40-80 Hz compared with the N group. The MI-VT(+) group had significantly smaller maximal values in the frequency ranges of 40-80 and 80-150 Hz than the MI-VT(-) group. These three groups were clearly differentiated by the maximal values of the 40-80-Hz QRS area map. CONCLUSIONS: It was suggested that the maximal value of the 40-80-Hz QRS area map was a new marker for VT after anterior MI.

Electrocardiography↗

PubMed1992

Dipyridamole electrocardiography test for the assessment of the severity of coronary artery disease.

The purpose of this study was to investigate the relationship of dipyridamole-induced ST changes to the severity of coronary artery disease. The subjects were 100 patients without myocardial infarction who underwent coronary arteriography for the diagnosis of coronary artery disease. The dipyridamole injection test (D) (0.568 mg/kg/4 min), and symptom-limited treadmill exercise test (T) were performed separately. Body surface electrocardiographic mapping of 87 leads was performed in both tests. The incidences of significant ST depression greater than or equal to 0.10 mV, number of leads showing significant ST depression (nST) and the maximal voltage of ST depression (maxST) in D and T were compared to the number of diseased coronary arteries. In patients without significant coronary stenosis (0VD group), the incidence of ST depression in the dipyridamole test was significantly lower than that in the treadmill test (D 9% vs T 47%, p less than 0.01). While, in one vessel disease (1VD), two vessel disease (2VD), and three vessel disease (3VD) groups, there was no significant difference in the incidence of ST depression between the dipyridamole test and the treadmill test (in 1VD, D 44% vs. T 65%; in 2VD, D 67% vs. T 93%; and in 3VD, D 93% vs. T 96%). In the dipyridamole test, nST was 0.6 +/- 2.4 in 0VD, 4.5 +/- 6.9 in 1VD, 4.1 +/- 4.5 in 2VD, and 10.6 +/- 8.1 in 3VD. Significant differences were found between 0VD and 1VD (P less than 0.05), 0VD and 3VD (P less than 0.01), 1VD and 3VD (P less than 0.01), and 2VD and 3VD (p less than 0.01). The maxST in the dipyridamole test was 0.02 +/- 0.04 mV in 0VD, 0.10 +/- 0.12 mV in 1VD, 0.13 +/- 0.11 mV in 2VD, and 0.22 +/- 0.11 mV in 3VD. Significant differences were found between 0VD and 1VD (p less than 0.01), 0VD and 2VD (p less than 0.01), 0VD and 3VD (p less than 0.01), 1VD and 3VD (p less than 0.01), and 2VD and 3VD (P less than 0.01). For the diagnosis of 3VD, the dipyridamole ECG test had as high a sensitivity (93% vs 96%), higher specificity (68% vs 38%, p less than 0.01), and higher predictive accuracy (75% vs 54%, p less than 0.01) than the treadmill test.(ABSTRACT TRUNCATED AT 400 WORDS)

Adult↗

PubMed1992

Dipyridamole electrocardiography test for the detection of severe coronary artery stenoses.

To investigate the relationship between dipyridamole-induced ST depression and the severity of coronary artery stenosis, the dipyridamole injection test (D) at 0.568 mg/kg/4 min, and the symptom limited treadmill exercise test (T) were performed separately in 16 normal volunteers and 167 patients who underwent coronary arteriography [91 patients without myocardial infarction (non-MI group) and 76 patients with previous myocardial infarction (MI group)]. Standard 12-lead electrocardiogram and body surface mapping of 87 leads were recorded in both tests. None of the normal volunteers had significant ST depression (greater than or equal to 0.10 mV) in D or T. Regarding the non-MI group, D had as high an incidence of ST depression as T (83% vs 93%) in patients with maximal coronary stenosis greater than or equal to 90%, while in those with maximum coronary stenosis less than 90%, D had a lower incidence of ST depression than T (16% vs 48%, p less than 0.01). For the MI group, the incidence of ST depression was compared to the maximal coronary artery stenosis supplying the non-infarcted area. In patients with maximal coronary artery stenosis greater than or equal to 90%, D had as high an incidence of ST depression as T (71% vs 64%). While, D had a lower incidence of ST depression than T (19% vs 35%, p less than 0.05) in those with maximum coronary artery stenosis less than 90%. For the diagnosis of coronary artery stenosis of greater than or equal to 90%, D had as high sensitivity (non-MI group, 82% vs 93%; MI group, 71% vs 64%) and higher specificity (non-MI group, 84% vs 52%, p less than 0.01; MI group, 81% vs 65%, p less than 0.05) compared with T. This study demonstrated that dipyridamole ECG is a sensitive and specific test to detect severe coronary artery stenosis.

Adult↗

PubMed1992

Presence of lower temperature-dependent antibody with low avidity to C100-3 (HCV) antigen in voluntary blood donors.

Serum samples with lower temperature-dependent antibody with low avidity to C100-3 (HCV) antigen were found in 0.19% of 23,197 voluntary blood donors at this blood center. They showed positive C100-3 antibody activity at 24 C but not at 37 C. The antibody activity bound to C100-3 antigen at lower temperature disappeared after incubation for 60 min at 37 C or treatment with 8 M urea. Other markers of hepatitis C virus infection, especially the presence of HCV-RNA were demonstrated in some of these serum samples and the importance of this phenomenon is discussed with regard to virus screening of blood donors for hepatitis C.

Antibody Affinity↗

PubMed1991

Signal-averaged body surface mapping for the assessment of low-amplitude potentials. Detailed maps during early ventricular activation in normal subjects.

Body surface isopotential maps around early ventricular activation were investigated in 30 normal subjects by the use of the authors' signal-averaged body surface mapping system. The number of beats averaged was 96-154 (mean, 127). Two distinct patterns were recognized in the appearance of a maximum at the onset of ventricular activation: the maximum in the first type (n = 16) was located on the right anterior chest; the maximum in the second type (n = 14) was on the central or left anterior chest. The site of the earliest ventricular activation was considered to be different in each of these types. During early ventricular activation, 25 subjects (83%) had two minima: one was on the left lateral chest and the other was on the left back. The two minima probably reflect two different receding activation fronts in the ventricles. The data in the present study are important to the understanding of the early ventricular activation process, as well as the diagnosis of heart diseases in which this process is disturbed.

Adolescent↗

PubMed1991

Cutting effectiveness and wear of carbide burs on eight machinable ceramics and bovine dentin.

As a first approach in evaluating the feasibility of industrial machinable ceramics in dentistry, we performed weight-load-cutting tests on eight machinable ceramics and bovine dentin, using #1557 carbide burs driven by an air-turbine handpiece. While the transverse load applied to the bur was cyclically varied between 20 and 80 g, we measured the cutting speed (i.e., the steady-state handpiece speed during cutting) and the cutting volume. The greater the applied load, the more the cutting speed decreased and the cutting volume increased. The degree of this trend, however, differed among the workpieces. When dentin and mica-based glass ceramics were being cut, the cutting speed was moderately reduced, the cutting effectiveness of the bur remained high, and the wear of the bur was small. When other ceramics--such as AIN-based, Si3N4-based, and CaO.SiO2-based ceramics--were being cut, however, the cutting speed was less diminished, and the cutting efficiency of the bur was smaller and decreased rapidly, along with extensive wear of the bur. We speculate that mica-based glass ceramics could be used as the substitute for dentin in the pre-clinical cutting exercise, and that another potential use of machinable ceramics examined might be in the production of future machined dental prostheses.

Animals↗

PubMed1991

Subcellular distribution of thyroxine 5'-monodeiodinase activity in rabbit kidney.

Thyroxine 5'-monodeiodinase is located in the proximal tubules of the rabbit kidney. To estimate the subcellular distribution of 5'-monodeiodinase activity, we prepared subcellular fractions, a basolateral membrane fraction and a brush border membrane fraction, from kidneys of Japanese white rabbits. Each fraction (0.5 mg protein) was incubated at 37 degrees C for 60 min with 0.5 micrograms T4 in the presence of 5 mM DTT. The T3 generated in the reaction mixture was extracted with cold ethanol and measured by RIA. For analysis of propylthiouracil-insensitive thyroxine 5'-monodeiodinase, we examined its kinetic behavior at nanomolar concentrations of the substrate, T4, in the presence of 100 microM propylthiouracil. In order of decreasing activity, basolateral membrane, microsomal fraction, mitochondrial fraction, cytosolic fraction, brush border membrane and nuclear fraction were capable of converting T4 to T3. Upon addition of 10(-5) M propylthiouracil to the reaction mixture, 5'-monodeiodinase activities of basolateral membrane and brush border membrane were inhibited by more than 90%, but that of microsomes was inhibited by only about 50%. In addition, kinetic analysis of microsomal 5'-monodeiodinase activity at nanomolar T4 concentrations in the presence of 10(-4) M propylthiouracil suggested on apparent Km of 3.8 nmol. These results indicate that there is high-Km 5'-monodeiodinase activity (PTU-sensitive) in the basolateral and brush border membranes and also high-Km and low-Km 5'-monodeiodinase (PTU-insensitive) in the microsomes of rabbit kidney.

Animals↗

PubMed1991

Residual monomers (TEGDMA and Bis-GMA) of a set visible-light-cured dental composite resin when immersed in water.

Rods of a visible-light-cured dental composite resin were photo-polymerized and immersed in water at 37 degrees C for 7 days. The residual monomers (TEGDMA and Bis-GMA) trapped in the set composite and those eluted into water were analysed by gas-liquid chromatography. It became evident that minor amounts of the residual monomers dissolved in water, but that most residual monomers remained in the set composite. Extension of the irradiation period contributed to the significant reduction in the residual monomer level and its elution into water.

Bisphenol A-Glycidyl Methacrylate↗

PubMed1991

Cellular mechanism of lithium-induced nephrogenic diabetes insipidus in rats.

One of the mechanisms by which Li evokes polyuria is thought to be impairment of arginine vasopressin (AVP)-sensitive adenylate cyclase (AdC) in cells of the renal collecting duct. To investigate how AdC is influenced by chronic administration of Li, we created nephrogenic diabetes insipidus (NDI) in rats and microdissected the medullary collecting tubule from both control and NDI rats. In the NDI group, the 10(-6) M AVP-stimulated cAMP contents failed to increase completely, and the levels were significantly lower than that of the control group (10.4 +/- 1.4 vs. 48.4 +/- 4.7 fmol/mm, P less than 0.001). Pretreatment with pertussis toxin (PT), an inhibitor of inhibitory G protein (Gi), did not affect the basal cAMP levels in both groups, although it increased AVP-stimulated cAMP production in the NDI group in a dose- and time-dependent manner. AVP-stimulated cAMP production with over 100 ng/ml PT in the NDI group reached the levels observed in the control group. Incubation with cholera toxin, an agonist of stimulatory G protein (Gs), increased the cAMP content in the two groups to almost equal levels. To exclude the possibility that prostaglandin E2 (PGE2) is involved in the cellular mechanism of Li-induced NDI, the effect of indomethacin (Indo) on PT action was examined. However, Indo (10(-5) M) did not influence either the basal or AVP-dependent cAMP contents. From these results it is suggested that Li impairs AVP-sensitive AdC not through inhibition of Gs but through activation of Gi and that PGE2 may not be involved in the cellular pathogenesis of NDI at least in the rat at the step of cAMP formation.

1-Methyl-3-isobutylxanthine↗

PubMed1991

Effect of altered activation sequence on epicardial QRST area and refractory period in dogs.

BACKGROUND: We investigated the effects of activation sequence on cardiac surface QRST areas and refractory periods in experiments on dogs. METHODS AND RESULTS: Right and left ventricular pacings were performed, and the pacing site was altered every 6 minutes. After 4 minutes of a given pacing, 54 unipolar electrograms distributed over the entire cardiac surface were recorded. Next, refractory periods at electrode sites near pacing electrodes were measured. Paired right ventricular/left ventricular (RV/LV) pacing data were obtained six or seven times in each sample. Although the QRST isoarea maps during the two activation orders were qualitatively similar, it was recognized consistently from the right ventricle-left ventricle difference map that leads around the RV free wall had positive values and that leads around the LV free wall and apex had negative values. Compared with the same leads at RV and LV pacing, QRST areas were larger when pacing sites were near the leads. The local QRST areas of individual leads at which we measured local refractory period were consistently larger during drive from proximal pacing sites than during drive from distant pacing sites. Refractory periods were consistently longer during proximal pacing than during distal pacing, and there was a positive correlation between change in local QRST area and change in refractory period (r = 0.64) during altered activation sequence, whereas there was an inverse correlation between change in QRST area and change in refractory period (r = -0.91) during localized myocardial warming. CONCLUSIONS: Both local QRST areas and local refractory periods were dependent on the activation sequence, and there was a positive correlation between QRST areas and refractory periods during various activation sequences compared with localized myocardial warming.

Animals↗

PubMed1991

Refractive-index-adjustable fillers for visible-light-cured dental resin composites: preparation of TiO2-SiO2 glass powder by the sol-gel process.

New fillers have been prepared for visible-light-cured (VL) dental resin composites with the refractive index adjustable to that of the resin phase. These SiO2 glass powders containing TiO2 up to 20 wt% were formed by heating to 1000 degrees C ground gels made from a mixture of Ti[OCH(CH3)2]4 and Si(OC2H5)4. With increasing TiO2 content, the refractive index of the prepared power increased linearly, while the optical transmittance at 467 nm decreased linearly. The experimentally formulated VL-cured resin composites, consisting of (TEGDMA and Bis-GMA) monomer mixture and TiO2-SiO2 glass filler, had greater transmittance when the refractive index of the filler matched that of the monomer mixture, resulting in a greater degree of monomer conversion upon irradiation with VL.

1-Propanol↗

PubMed1991

Signal-averaged body surface mapping for the assessment of low-amplitude potentials. Relation between ventricular depolarization and repolarization in normal subjects.

To examine the relation between ventricular depolarization and repolarization, body surface isopotential maps at the end of the QRS complex were studied in 32 normal subjects using a signal-averaged body surface mapping system. The number of beats averaged was 96-154 (mean 126.2). In this study, there were 8 types of isopotential map patterns at the end of the QRS complex. Mean +/- SD of QRS duration, appearance time of repolarization, and disappearance time of depolarization were 82.0 +/- 8.7 msec, 71.8 +/- 10.5 msec, and 79.7 +/- 9.4 msec, respectively. Time duration of overlapping depolarization and repolarization was 8.6 +/- 6.4 msec. The early repolarization was widely distributed on the left anterior chest and the upper sternal region. These results demonstrated the difference between the appearance time of repolarization and the disappearance time of depolarization for each lead. We concluded that it is difficult to evaluate ECG waves in the terminal portion of the QRS complex with the dipolar theory only.

Adolescent↗