E Tanaka

The Jikei University School of Medicine, Edo, Tokyo, Japan

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Publications (65)89.17 Total impact

  • K Komukai · E Tanaka · S Kurihara
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    ABSTRACT: Contraction of cardiac muscle is regulated by intracellular Ca2+ concentration ([Ca2+]i) change. The Ca2+ increased by the action potential is removed by Ca2+ removal mechanisms (sarcoplasmic reticulum, Na-Ca exchanger and Ca pump of the surface membrane) and is also bound to troponin. However, under some specific conditions which induced an overload of Ca2+, oscillatory changes in [Ca2+]i, which are considered to be due to regenerative Ca2+ release from the sarcoplasmic reticulum, appear. In Ca2+ overload, a transient increase in [Ca2+]i is observed after the falling phase of the Ca2+ transient which is induced by electrical stimulation. In accordance with the transient increase in [Ca2+¿i, the membrane transiently depolarizes (delayed after-depolarization). This membrane depolarization is considered to be due to the inward currents through the Na-Ca exchanger and non-specific cation channels. If the depolarization is large enough to reach the threshold, the action potentials are triggered (triggered activity). Thus, an increase in [Ca2+]i is one of possible factors in triggering of arrhythmia.
    No preview · Article · Sep 1996 · Nippon rinsho. Japanese journal of clinical medicine
  • E. Tanaka · N. Nohara · T. Tomitani · M. Yamamoto

    No preview · Chapter · Jan 1996
  • T Tanaka · K Komukai · M Kawai · E Tanaka · S Kurihara
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    ABSTRACT: We investigated the effects of thapsigargin (TG) (0.1-1 microM) on the relation between intracellular Ca2+ concentration and tension in ferret papillary muscles using aequorin-injected and skinned preparations. Aequorin was injected into the superficial cells of ferret papillary muscles; the Ca2+ signals of aequorin and tension in twitch and those with the application of 15 mM caffeine were simultaneously measured. The alteration of Ca2+ sensitivity of the contractile elements was examined by measuring the pCa-tension relation in Triton-X-treated skinned preparations. TG decreased the peak of the Ca2+ signal accompanied by a prolonged decay time. However, the tension was scarcely altered even at 1 microM TG. TG inhibited the caffeine-induced Ca2+ signal. Prolongation of decay of the Ca2+ signal by TG in twitch was further enhanced by isoprenaline (10 nM). The pCa-tension relation of the skinned preparation was slightly but significantly shifted to the right by TG. The apparent dissociation of the effects of TG on the Ca2+ signal and tension in intact preparations is not a result of alteration of the Ca2+ sensitivity of the myofilaments. The effects of TG in multicellular preparations are probably limited to the outer layer of the preparation. The slower time course of the Ca2+ signal induced by TG is due to the inhibition of Ca2+ uptake by sarcoplasmic reticulum, which is more significantly observed when the intracellular Ca2+ transient is increased by isoprenaline.
    No preview · Article · Oct 1995 · Cardiovascular Research
  • S Kurihara · K Hongo · T Tanaka · E Tanaka
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    ABSTRACT: We investigated the effects of a newly synthesized dihydropyridine (DHP) derivative (NZ-105) on intracellular Ca transients and contraction in ferret ventricular muscles, using the aequorin method. Low concentrations of NZ-105 (10(-9)-10(-7) M) showed no significant effects on the light signal of aequorin and tension in twitch. High concentrations of NZ-105 (10(-6)-10(-5) M) inhibited the peaks of the light signal and tension without altering their time courses. The relation between the peaks of the light signal and tension in twitch, measured in solutions with varying Ca2+ concentrations, was shifted to the left by NZ-105. The relation between [Ca2+]i and tension measured in tetanic contraction was also shifted to the left by NZ-105. These results suggest that the inhibitory effect of NZ-105 on contraction in mammalian cardiac muscle is curtailed by an increase in Ca sensitivity of the contractile elements.
    No preview · Article · Sep 1994 · Journal of Cardiovascular Pharmacology
  • K Shimizu · N Satoh · H Uchida · E Tanaka
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    ABSTRACT: We are developing a time-of-flight (TOF) multiprobe imaging system, which is used to determine the distribution of the administered tracer substances labeled with positron emitting nuclides. A prototype system has eight detector probes, each that consists of a BaF<sub>2</sub> scintillator and a fast photomultiplier tube. The system construction is simple compared to positron emission tomographs by virtue of using TOF information of annihilation. We have studied the time resolution for different shapes of BaF<sub>2</sub> scintillators by Monte Carlo simulations and experiments, and found that truncated pyramid shaped crystals provided good time resolution with reasonable sensitivity. Coincidence time resolution of 180 to 200 ps were obtained with 16 combinations of the detectors in the system. An iterative algorithm for image reconstruction using TOF data was proposed. By introducing a proper deblurring algorithm into the image reconstruction process, the spatial resolution can be improved by a factor of two without significant amplification of noise, which corresponds to a spatial resolution of 1.5 cm
    No preview · Conference Paper · Jun 1994
  • Source
    Y Saeki · S Kurihara · K Hongo · E Tanaka
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    ABSTRACT: 1. To study the effects of mechanical constraints on the calcium (Ca2+) affinity of cardiac troponin C, we analysed the tension and aequorin light (AL, intracellular Ca2+) transients in response to a step length change in aequorin-injected ferret right ventricular papillary muscles. The muscle preparations were continuously activated with ouabain (10(-4) M) (ouabain contracture) or with high frequency stimuli in the presence of ryanodine (5 microM) (tetanic contraction). 2. The tension transient in response to either the release or stretch was oscillatory: tension decreased rapidly during the release and then increased, after which it lapsed into a new steady level in a series of damped oscillations. The opposite was true for the stretch. The oscillatory responses were conspicuous and less damped in ouabain-activated preparations (oscillation frequency of 2.2-2.3 Hz at 22 degrees and 4.5-4.6 Hz at 30 degrees C) and much more damped in ryanodine-treated preparations. 3. The transient AL response was also oscillatory, the time course of which corresponded to that of the transient tension response. Regardless of the difference in the time course of the transients in two different preparations and at two different temperatures, the increase in AL corresponded to the decrease in tension, likewise the decrease in AL to the increase in tension. 4. The mean level of AL after release was lower than the control level present just prior to the release in ouabain-activated preparations, but the AL after release finally returned to the nearly control level in ryanodine-treated preparations. 5. When the ryanodine-treated muscle was further treated with 2,3-butanedione monoxime (BDM) (20 mM), the tetanic tension decreased remarkably without affecting the AL signal. The tension transient of this preparation was quite similar to that of the resting muscle, which changed in a nearly stepwise fashion; AL was hardly affected by step length changes, as in the resting muscle, in spite of the higher AL level. 6. These results suggest that the Ca2+ affinity of cardiac troponin C is increased with an increase in tension (i.e. the cross-bridge attachment) and decreased with a decrease in tension i.e. the cross-bridge detachment), and that the mean [Ca2+]i is lowered by release, at least in a Ca(2+)-overloaded condition, mainly through the sarcoplasmic reticulum.
    Full-text · Article · May 1993 · The Journal of Physiology
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    K Hongo · E Tanaka · S Kurihara
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    ABSTRACT: 1. We investigated the mechanism of signal transduction during the effect of muscarinic receptor stimulation on Ca2+ transients, tension, Ca2+ sensitivity and the cross-bridge cycling rate (CCR). 2. Membrane-permeable derivatives of cyclic GMP (8-bromo-cyclic GMP and dibutyryl cyclic GMP) did not cause any significant changes in the peaks of Ca2+ transients and tension and the time courses of either signal modulated by isoprenaline (Iso) (0.1 microM). 3. Nitroprusside (0.1-1 mM) likewise did not change the peaks or the time courses of Ca2+ transients and tension in the Iso-treated preparations. 4. In papillary muscles excised from ferrets treated with pertussis toxin (islet-activating protein, IAP), which is known to abolish the function of GTP-binding proteins (Gi, Go and Gt), similar changes in Ca2+ transients and tension produced by treatment with Iso (0.1 microM) were noted as in non-IAP-treated preparations. However, no effects of acetylcholine (ACh; 1 microM) on either signal were observed. 5. The relation between [Ca2+]i and tension measured during the steady state of tetanic contraction was shifted to the right by Iso (0.1 microM), and cyclic GMP derivatives (1 mM) did not change the altered relation. In the IAP-treated preparations, ACh (1 microM) did not influence the relation altered by Iso (0.1 microM). 6. Cyclic GMP derivatives (1 mM) did not alter the Iso (0.1 microM)-increased CCR measured by perturbation analysis. ACh (1 microM) did not restore the Iso-increased CCR in the IAP-treated preparations. 7. These results suggest that signal transduction in muscarinic receptor stimulation is primarily mediated by inhibition of adenylate cyclase via IAP-sensitive GTP-binding proteins, and that cyclic GMP does not play an important role in the effect of muscarinic receptor stimulation on Ca2+ transients, tension, Ca2+ sensitivity or CCR.
    Full-text · Article · Mar 1993 · The Journal of Physiology
  • Source
    K Hongo · E Tanaka · S Kurihara
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    ABSTRACT: 1. To clarify the mechanism which regulates the time course of twitch tension when beta- and muscarinic receptors are stimulated, intracellular Ca2+ transients, Ca2+ sensitivity of the contractile element and the cross-bridge cycling rate (CCR) were measured in ferret ventricular muscles. 2. Isoprenaline (Iso; 0.1 microM) increased peaks of Ca2+ transients measured with aequorin and tension, and abbreviated the time courses of both signals. Addition of acetylcholine (ACh; 0.01-1 microM) to the Iso-treated preparation dose dependently decreased the peaks of both signals and restored the time course of Ca2+ transients. However, the time course of tension was not recovered by the addition of ACh, and the relaxation time in particular, was further shortened by ACh. Carbachol (1 microM) applied to the Iso-treated preparation yielded similar results. 3. [Ca2+]i and tension at a quasi-steady level of tetanic contraction, which was produced by ryanodine (5 microM) and repetitive stimulation, were measured and Ca2+ sensitivity of the contractile element was estimated. Iso (0.1 microM) decreased the Ca2+ sensitivity and the addition of ACh (1 microM) completely recovered it to the control level. 4. In order to measure CCR, the perturbation analysis method was applied to steady-state tension of tetanic contraction. The CCR was not altered even when the tetanic tension level was decreased to 50% by decreasing [Ca2+]o. Iso (0.1 microM) slightly decreased the tetanic tension level and increased the CCR from 2.73 to 3.25 Hz. The effect of Iso was observed when the Iso-decreased tension was recovered by an increase in [Ca2+]i. The addition of ACh (1 microM) recovered the CCR which was increased by Iso, to the control level. Atropine (10 microM) blocked the effect of ACh, and carbachol (1 microM) restored the CCR increased by Iso to the control level. 5. The time course of Ca2+ transients, Ca2+ sensitivity and CCR were antagonistically regulated by beta- and muscarinic receptor stimulation, but the time course of tension did not parallel the changes in these parameters. Therefore, these results suggest that the time course of tension, particularly the relaxation time, is not determined by the time course of Ca2+ transients, Ca2+ sensitivity and the CCR, and that other factors might be involved in the regulation of the time course of tension when beta- and muscarinic receptors are stimulated.
    Full-text · Article · Mar 1993 · The Journal of Physiology
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    ABSTRACT: In the PET system a block detector, which is a position-sensitive photomultiplier (PMT) tube coupled to four arrays of 1.7-mm-wide BGO crystals, is utilized. Fifteen block detectors are positioned to form a 35-cm-diameter ring, with four BGO arrays coupled to each PMT. This provides four detector rings, giving the system a 7-slice imaging capability. The gantry head tilts up to +/-90 degrees , and is capable of moving up and down by 30 cm. These positioning capabilities allow flexibility and great ease of use in subject positioning. A gantry entrance size of 22 cm in diameter allows studies ranging from rats and mice to primates such as Rhesus and squirrel monkeys. The physical performance of the system has been evaluated.
    No preview · Article · Feb 1992 · IEEE Transactions on Medical Imaging
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    ABSTRACT: A high-resolution positron emission tomograph (PET) for brain studies has been developed. It consists of five detector rings (240 BGOs/ring). New multisegment photomultiplier tubes (PMTs) were adopted for the system with 5-mm-wide BGOs. The system is designed to examine a patient sitting or lying down on a chair/bed couch. The functions of PMT auto gain control and real-time image display are implemented in the system. The physical performance of the system was evaluated: the spatial resolution is 3.5 mm in the transaxial plane and 5.7 mm in the axial direction, and the total system sensitivity is 109 kcps/μCi/ml for a uniform phantom 20 cm in diameter with a pulse height threshold of 350 keV
    No preview · Article · May 1990 · IEEE Transactions on Nuclear Science
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    ABSTRACT: A simple time-of-flight (TOF) positron imaging method is proposed in which the spatial resolution obtained with TOF information is improved by a novel iterative algorithm. The prototype has a pair of opposed detectors using BaF<sub>2</sub> (2×2×2 cm<sup>3</sup>) and photomultiplier tubes (18.5-mm diameter). The measured TOF resolution full width at half maximum was 330 ps, which corresponds to 5.0 cm of spatial resolution for source localization between the detectors. Eight iterations with the algorithm improve the spatial resolution by a factor of about two for a point source. The algorithm is based on modifications of a Bayesian deconvolution algorithm. For more complex sources, it takes more iterations (e.g. 80); however the algorithm is about five times faster than the original Bayesian algorithm
    No preview · Article · Mar 1989 · IEEE Transactions on Nuclear Science
  • H Murayama · E Tanaka · N Nohara · T Tomitani · M Yamamoto

    No preview · Article · Jul 1987 · Kaku igaku. The Japanese journal of nuclear medicine
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    ABSTRACT: This paper describes evaluation and correction of count rate characteristics of POSITOLOGICA II, a multi-slice whole body positron emission tomography system. The present study was performed using three phantoms; a 5 cm inner diameter, water-filled lucite cylinder, a 20 cm inner diameter, water-filled lucite cylinder and a chest phantom. After injection of high activity (about 1.85 GBq (50 mCi] of 13N ammonia into each phantom, rates of true coincidence, random coincidence and single photon detections were measured during decay of the isotope through more than two orders of magnitude of activity. At very high levels of activity, count rate characteristics of the system were saturated and limited to 660 kcps of total coincidence rate, which was the sum of rates in on-time and off-time windows, by the FIFO (first-in first-out) output frequency. Below those levels of activity the relationship between count loss and true coincidence rate was not unique but depended on the phantom configurations, suggesting that count loss correction using the above relationship was inadequate for quantitative study. However, the relationship between count loss and single rate was almost independent of the phantom configurations. Thus in conclusion count loss could be corrected using single rate for POSITOLOGICA II. A practical method of count loss correction was also proposed.
    No preview · Article · May 1987 · Radioisotopes
  • Norimasa Nohara · Hideo Murayama · Eiichi Tanaka
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    ABSTRACT: Single photon emission computed tomography (SPECT) systems are proposed which provide images with improved signal-to-noise ratio. The systems consist of gamma cameras equipped with collimators which view an object to be imaged with an increased sampling density in the vicinity of the center of a field-of-view. The detection systems produce weighted projection data. Evaluation was made with respect to noise characteristics in images resulting from such systems. Simulation studies showed that dual and quadruple camera systems equipped with a combination of fan beam collimators result in noise reduction of about 37% at the center of image and uniform noise over an image area, compared with systems equipped with parallel hole collimators. This suggests that the proposed systems have a possibility of improvement on quantitation of SPECT.
    No preview · Article · Mar 1987 · IEEE Transactions on Nuclear Science
  • H Murayama · N Nohara · E Tanaka

    No preview · Article · Oct 1986 · Kaku igaku. The Japanese journal of nuclear medicine
  • E Tanaka · N Nohara · T Tomitani · M Yamamoto · H Murayama
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    ABSTRACT: Feasibility of stationary positron emission tomography (PET) using discrete detectors has been investigated by simulation studies. To enable full utilization of detector resolution, a "bank array" of detectors is proposed and an EM algorithm is adopted for image reconstruction. The bank array consists of an odd number of detector banks arranged on a circular ring with a gap equal to one half the detector width. The EM algorithm [11] is used with some modifications for reducing the quantity of computation, improving the convergence speed, and suppressing statistical noise, so as to meet the present purpose. Simulation studies involving several phantoms show that the stationary PET with the new detector array provides image quality which is good enough for clinical applications. For fast dynamic studies with low spatial resolution, the convolution-backprojection method is efficient, but for high-resolution static imaging, resolution enhancement by an iterative method is required. Problems arising in the corrections for attenuation of photons and detector sensitivity, etc., are also discussed. A totally stationary PET avoids the mechanical problems associated with accurate movement of heavy assemblies and is particularly advantageous in gated cardiac imaging or in fast dynamic studies. Elimination of a scan along the detector plane allows a quick scan in the axial direction to achieve three-dimensional imaging with a small number of detector rings.
    No preview · Article · Feb 1986 · IEEE Transactions on Medical Imaging
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    ABSTRACT: A single ring high resolution positron CT for animal studies was developed which utilizes 64 gridded rectangular photomultipliers (l3mm square) and 128 rectangular Bismuth Germanate crystal (4mm wide, 10mm high and 20mm long). A photomultiplier is incorporated with a grid near the photocathode which controls photoelectron transport of half part of a tube. This enalbes us the identification of the fired crystal out of two coupled to a photomultiplier. Detector ring, animal port and field of view diameters are 265, 135 and 128mm, respectively. Detector arrangement was determined by POSITOLOGY. The spatial resolutions in fwhm after unfolding source spread (2mm dia.) were 2.2mm at center and 3.3mm (tangential) and 3.6mm(radial) at 60mm from the center. Hardware out-of-FOV event rejector was implemented which rejects events outside the field of view and reduces event rate by a factor of 3 in the case of calibration measurements.
    No preview · Article · Mar 1985 · IEEE Transactions on Nuclear Science
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    ABSTRACT: Performance of positron emission computed tomographs having spatial resolution as high as 3 mm FWHM was analytically evaluated. Increases in widths of line spread functions due to positron range and angular deviation were estimated. The slice thickness should be thin in accordance with the resolution in transverse axial plane. Singles rate, true coincidence rate, and scattered coincidence rate with high resolution tomographs of small diameter detector rings were estimated for three types of thin slice collimators. Feasibility of high resolution positron tomographs with small detector rings was discussed with applications to animal study.
    No preview · Article · Mar 1985 · IEEE Transactions on Nuclear Science
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    ABSTRACT: Twin BGO detectors and timing pulse shape discriminators for crystal identification have been developed for high spatial resolution positron emission tomography. Each detector consists of two BGO crystals and one single photomultiplier tube. The tube has a grid covering half the area of the photocathode window, and opposite to which stands one of the BGO crystals. The amplitude of the anode signals for the scintillation events in the grid side crystal is modulated by supplying negative pulses to the grid. Crystal identification is achieved by pulse shape discrimination for the detector signals.The design criteria of the electronic system and the performance are described. With suitable pulse shape discrimination, the erroneous positioning due to statistical noise is negligible and the coincidence time resolution for annihilation photon pairs is about 5.8 ns fwhm.
    No preview · Article · Apr 1984 · Nuclear Instruments and Methods in Physics Research
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    ABSTRACT: A 3-detector ring, 5-slice whole-body positron CT has been developed and is being tested. The PCT, POSITOLOGICA-II, has a total of 480 BGO's (160/ring), and employs continuous rotation scan (0.5rps). By using a 15mm wide BGO, a 9.2mm FWHM spatial resolution for reconstructed image is obtained at the center of FOV. Measured phantom diameter dependence of the true count rate shows good agreement with theoretically anticipated characteristics, including maximum sensitivity at around 30cm dia. Sensitivities for 20cm dia. phantom are 28 and 38 kcps/¿Ci/ml for in-plane and cross-plane, respectively, including scattered coincidences. Relative system detection efficiency measured with a line source at FOV center is 96% at 15ns time window (90% at 12ns), basing on 100% efficiency in 20-24ns.
    No preview · Article · Mar 1983 · IEEE Transactions on Nuclear Science

Publication Stats

624 Citations
89.17 Total Impact Points

Institutions

  • 1994-1995
    • The Jikei University School of Medicine
      • Department of Cell Physiology
      Edo, Tokyo, Japan
  • 1992
    • HAMAMATSU Photonics K.K.
      Hamamatu, Shizuoka, Japan
  • 1964-1990
    • National Institute of Radiological Sciences
      Tiba, Chiba, Japan
  • 1982
    • Chiba Institute of Science
      Tiba, Chiba, Japan