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Seiryo Sugiura

Publications and source records attributed to Seiryo Sugiura.

15 recordsLinked to original sources
PubMed2006

Membrane potential of rat ventricular myocytes responds to axial stretch in phase, amplitude and speed-dependent manners.

OBJECTIVE: To elucidate the interdependence between the mechanical state of the myocardium and its electrical activity, previous studies have been performed at the cellular level. However, the information to date has been limited by the technical difficulties associated with stretching single myocytes. METHODS: We solved this problem by combining two techniques, namely a carbon fiber technique for stretching rat myocytes with wide ranges of amplitude and speed, and ratiometric measurement of a fluorescent indicator (di8-ANEPPS) for evaluating the membrane potential in the non-contact mode. RESULTS: During systole, stretching caused depolarization that prolonged the action potential duration without affecting the peak amplitude, but the effect was only significant in the late phase. Application of a stretch to quiescent myocytes depolarized the membrane potential in amplitude- and speed-dependent manners, but the response was suppressed by cytochalasin D treatment, suggesting participation of the cytoskeleton in the mechanotransduction mechanism. Finally, ion replacement experiments revealed that although Na+ was the dominant charge carrier for large amplitude stretches, Ca2+ permeation was involved in small amplitude stretches, suggesting amplitude-dependent ion selectivity. CONCLUSIONS: Application of axial stretching to rat ventricular myocytes changed the membrane potential in phase-, amplitude- and speed-dependent manners. Amplitude may also modulate the ion selectivity of stretch-activated channels.

Animals↗
PubMed2006

Expression of green fluorescent protein impairs the force-generating ability of isolated rat ventricular cardiomyocytes.

Green fluorescent protein (GFP) is widely used as a biologically inert expression marker for studying the effects of transgene expression in heart tissue, but its influence on the contractile function of cardiomyocytes has not yet been fully evaluated. We measured the contractile function of isolated rat ventricular myocytes before and after infection with a recombinant adenovirus expressing GFP (Adv-GFP). Myocytes infected with a non-transgene-containing adenovirus (Adv-Null) or uninfected myocytes (UI) served as controls. Using a carbon-fiber-based force-length measurement system for single cardiomyocytes, we evaluated the contractile function over a wide range of loading conditions including the shortening fraction (%FS) and maximal shortening velocity (Vmax) under the unloaded condition, and isometric force. At 24 hours after infection, nearly 80% of the Adv-GFP-infected myocytes expressed GFP. We found that the %FS and Vmax did not differ among the three groups, however, the isometric force showed a mild, but significant, decrease only in Adv-GFP myocytes (Adv-GFP: 29.1 +/- 4.0 mN/mm2; Adv-Null: 42.8 +/- 6.2 mN/mm2; UI: 47.1 +/- 4.8 mN/mm2; p = 0.03). An evaluation of the contractile function of isolated cardiomyocytes under high load conditions revealed impaired isometric contractility by GFP expression. Adv-GFP expression may not be an ideal control for specific gene expression experiments in myocardial tissue.

Adenoviridae↗
PubMed2005

Microtubules modulate the stiffness of cardiomyocytes against shear stress.

Although microtubules are involved in various pathological conditions of the heart including hypertrophy and congestive heart failure, the mechanical role of microtubules in cardiomyocytes under such conditions is not well understood. In the present study, we measured multiple aspects of the mechanical properties of single cardiomyocytes, including tensile stiffness, transverse (indentation) stiffness, and shear stiffness in both transverse and longitudinal planes using carbon fiber-based systems and compared these parameters under control, microtubule depolymerized (colchicine treated), and microtubule hyperpolymerized (paclitaxel treated) conditions. From all of these measurements, we found that only the stiffness against shear in the longitudinal plane was modulated by the microtubule cytoskeleton. A simulation model of the myocyte in which microtubules serve as compression-resistant elements successfully reproduced the experimental results. In the complex strain field that living myocytes experience in the body, observed changes in shear stiffness may have a significant influence on the diastolic property of the diseased heart.

Animals↗
PubMed2005

Contractile dysfunction of cardiomyopathic hamster myocytes is pronounced under high load conditions.

To understand the pathophysiology of hereditary cardiomyopathy, the contractile function of cardiomyopathic hamsters has been studied at the cellular level. However, most of the studies to date have described the cell shortening under the unloaded condition. Using a novel force-length measurement system for single cardiomyocytes, we studied the contractile function of cardiomyopathic hamster myocytes over a wide range of loading conditions. Cardiomyocytes were isolated from the ventricles of eight- to 10-week-old cardiomyopathic (CMP) hamsters (Bio TO-2 strain), as well as control (CTRL) Syrian hamsters. A pair of carbon fibers was attached to both ends of single cardiomyocytes and their contractile characteristics were recorded while changing the after-load by controlling the fiber motion. Under the unloaded condition, the shortening fraction (CMP 9.2+/-0.5% vs. CTRL 10.7+/-0.8%, P=0.06) and maximum shortening velocity (CMP 98.2+/-7.3 microm/s vs. CTRL 147.2+/-6.5 microm/s, P<0.05) were decreased in CMP hamster myocytes. The peak force under the isometric condition (CMP 35.8+/-2.2 mN/mm2 vs. CTRL 69.0+/-8.4 mN/mm2, P<0.05) and external work (CMP 898+/-130 J/m3 vs. CTRL 3058+/-576 J/m3, P<0.05) under physiologically loaded conditions were also decreased, but the differences were more pronounced under the loaded conditions. Calcium transients measured by Indo-1 revealed elevated diastolic level, decreased peak level, and slower diastolic decay in CMP myocytes thus being consistent with the observed contractile dysfunction. These results clearly indicate the importance of the loading conditions in evaluating the contractile function of CMP hamster myocytes, and may provide insights into the mechanism of contractile dysfunction in this disease.

Animals↗
PubMed2004

Three-dimensional simulation of calcium waves and contraction in cardiomyocytes using the finite element method.

To investigate the characteristics and underlying mechanisms of Ca(2+) wave propagation, we developed a three-dimensional (3-D) simulator of cardiac myocytes, in which the sarcolemma, myofibril, and Z-line structure with Ca(2+) release sites were modeled as separate structures using the finite element method. Similarly to previous studies, we assumed that Ca(2+) diffusion from one release site to another and Ca(2+)-induced Ca(2+) release were the basic mechanisms, but use of the finite element method enabled us to simulate not only the wave propagation in 3-D space but also the active shortening of the myocytes. Therefore, in addition to the dependence of the Ca(2+) wave propagation velocity on the sarcoplasmic reticulum Ca(2+) content and affinity of troponin C for Ca(2+), we were able to evaluate the influence of active shortening on the propagation velocity. Furthermore, if the initial Ca(2+) release took place in the proximity of the nucleus, spiral Ca(2+) waves evolved and spread in a complex manner, suggesting that this phenomenon has the potential for arrhythmogenicity. The present 3-D simulator, with its ability to study the interaction between Ca(2+) waves and contraction, will serve as a useful tool for studying the mechanism of this complex phenomenon.

Animals↗
PubMed2004

Single cell mechanics of rat cardiomyocytes under isometric, unloaded, and physiologically loaded conditions.

One of the most salient characteristics of the heart is its ability to adjust work output to external load. To examine whether a single cardiomyocyte preparation retains this property, we measured the contractile function of a single rat cardiomyocyte under a wide range of loading conditions using a force-length measurement system implemented with adaptive control. A pair of carbon fibers was used to clamp the cardiomyocyte, attached to each end under a microscope. One fiber was stiff, serving as a mechanical anchor, while the bending motion of the compliant fiber was monitored for force-length measurement. Furthermore, by controlling the position of the compliant fiber using a piezoelectric translator based on adaptive control, we could change load dynamically during contractions. Under unloaded conditions, maximal shortening velocity was 106 +/- 8.9 microm/s (n = 13 cells), and, under isometric conditions, peak developed force reached 5,720 nN (41.6 +/- 5.6 mN/mm(2); n = 17 cells). When we simulated physiological working conditions consisting of an isometric contraction, followed by shortening and relaxation, the average work output was 828 +/- 123 J/m(3) (n = 20 cells). The top left corners of tension-length loops obtained under all of these conditions approximate a line, analogous to the end-systolic pressure-volume relation of the ventricle. All of the functional characteristics described were analogous to those established by studies using papillary muscle or trabeculae preparations. In conclusion, the present results confirmed the fact that each myocyte forms the functional basis for ventricular function and that single cell mechanics can be a link between subcellular events and ventricular mechanics.

Animals↗
PubMed2004

Amlodipine increases nitric oxide production in exhaled air during exercise in patients with essential hypertension.

BACKGROUND: Endothelial production of nitric oxide (NO) is attenuated in patients with essential hypertension. We investigated whether treatment with amlodipine increased exhaled NO output (VNO) at rest and during exercise in patients with essential hypertension. METHODS: We studied the effect of amlodipine in seven untreated hypertensive patients. Cardiopulmonary exercise testing and NO measurement of exhaled air were performed on these patients before and after 2 months of amlodipine treatment. RESULTS: Amlodipine decreased blood pressure (BP) both at rest and during exercise (at rest: 147.1 +/- 6.4 [SEM]/89.9 +/- 4.4 v 133.6 +/- 5.4/82.7 +/- 3.9 mm Hg, P <.05; at peak exercise: 224.9 +/- 8.0/113.1 +/- 5.3 v 207.0 +/- 6.0/100.7 +/- 5.0 mm Hg, P <.05) without affecting heart rate (at rest: 67.6 +/- 3.9 v 70.4 +/- 4.5 beats/min, P =.33; peak exercise: 146.4 +/- 7.4 v 144.0 +/- 7.2 beats/min, P =.49). Amlodipine did not affect minute ventilation (VE) at rest or during exercise. It did not alter anaerobic threshold, peak oxygen uptake (peak VO(2)), or peak workload. However, after amlodipine treatment, VNO was significantly greater both at rest (130.8 +/- 19.4 v 180.4 +/- 24.8 nL/min, P <.05) and at peak exercise (380.0 +/- 47.5 v 582.6 +/- 74.3 nL/min, P <.05). CONCLUSIONS: Amlodipine increased NO production, at least in the pulmonary circulation, in patients with essential hypertension. In addition to its antihypertensive effect, the enhancement of NO production by amlodipine in the vasculature of other organs may contribute to its beneficial effects on the cardiovascular system.

Adult↗
PubMed2004

Role of Ca2+ in determining the rate of tension development and relaxation in rat skinned myocardium.

To clarify the roles of Ca2+ and crossbridge kinetics in determining the cardiac contraction profile, we analyzed the rate of tension development following nitrophenyl-EGTA photolysis and the rate of relaxation following diazo-2 photolysis in the absence and presence of phosphate (Pi, 5 mM) in rat skinned ventricular trabeculae. The rate of tension development was fitted with a single exponential function. The rate constant (kc) increased not only with an increase in prephotolysis tension (initial activation level) under the same postphotolysis tension (final Ca2+ level), but also with an increase in postphotolysis tension under the same prephotolysis tension. Pi increased kc, though decreased both the prephotolysis and postphotolysis tension greatly. The rate of relaxation was fitted with a double-exponential function. The rate constants of both initial rapid phase (kr1), which was higher than kc, and subsequent slow (kr2) relaxation were almost independent of either the prephotolysis tension or the postphotolysis tension (i.e. the extent of relaxation). Pi increased both kr1 and kr2 by about twofold. These results apparently contradicting both the "steric blocking model" and the "kinetic model", and can be explained in terms of the changes in number of tension-generating crossbridges through the Ca2+-dependent cooperative thin filament activation/inactivation associated with the Pi-modulated changes in number of tension-generating crossbridges. The thin filament activation kinetics seems to be slower than its inactivation.

Animals↗
PubMed2004

Multiphysics simulation of left ventricular filling dynamics using fluid-structure interaction finite element method.

To relate the subcellular molecular events to organ level physiology in heart, we have developed a three-dimensional finite-element-based simulation program incorporating the cellular mechanisms of excitation-contraction coupling and its propagation, and simulated the fluid-structure interaction involved in the contraction and relaxation of the human left ventricle. The FitzHugh-Nagumo model and four-state model representing the cross-bridge kinetics were adopted for cellular model. Both ventricular wall and blood in the cavity were modeled by finite element mesh. An arbitrary Lagrangian Eulerian finite element method with automatic mesh updating has been formulated for large domain changes, and a strong coupling strategy has been taken. Using electrical analog of pulmonary circulation and left atrium as a preload and the windkessel model as an afterload, dynamics of ventricular filling as well as ejection was simulated. We successfully reproduced the biphasic filling flow consisting of early rapid filling and atrial contraction similar to that reported in clinical observation. Furthermore, fluid-structure analysis enabled us to analyze the wave propagation velocity of filling flow. This simulator can be a powerful tool for establishing a link between molecular abnormality and the clinical disorder at the macroscopic level.

Biophysical Phenomena↗
PubMed2003

Myosin light chain isoforms modify force-generating ability of cardiac myosin by changing the kinetics of actin-myosin interaction.

OBJECTIVE: To investigate the functional role of myosin light chain (MLC) isoforms in cardiac muscles, we examined the motor function of two different myosins the structure of which differed only in the MLC. METHODS: We purified myosin from atria (A-myosin) and ventricles (V-myosin) of young rats, which contained atrial-type and ventricular-type MLCs, respectively, but having identical alpha-heavy chain isoform. Actin filament velocity (Vel) was determined in the in vitro motility assay. Average force of myosin molecules (F) was estimated and single events of actin-myosin interaction were recorded with the laser trap technique. RESULTS: Vel was slightly higher in A-myosin than in V-myosin, while actin-activated ATPase activity was not different. F, determined from force versus actin filament length relation, was approximately 60% higher in V-myosin (3.3 vs. 2.1 pN/microm). The mean duration of isometric force events was longer in V-myosin than in A-myosin (323+/-13 vs. 294+/-30 ms, p<0.05), while the amplitudes of unitary displacement and force of a single myosin molecule did not differ between them. CONCLUSION: The MLC isoform can be a determinant of force-generating ability of cardiac myosin by modulating crossbridge kinetics without affecting the catalytic activity.

Actin Cytoskeleton↗
PubMed2003

Unloaded shortening increases peak of Ca2+ transients but accelerates their decay in rat single cardiac myocytes.

It is of paramount importance to investigate the relation between the time-dependent change in intracellular Ca2+ concentration ([Ca2+]i) (Ca2+ transients) and the mechanical activity of isolated single myocytes to understand the regulatory mechanisms of heart function. However, because of technical difficulties in performing mechanical measurements with single myocytes, the simultaneous recording of Ca2+ transients and mechanical activity has mainly been performed with multicellular cardiac preparations that give conflicting results concerning Ca2+ transients during isometric twitches and during twitches with unloaded shortening. In the present study, we coupled intracellular Ca2+ measurement optics with a force measurement system using carbon fibers to examine the relation between Ca2+ transients and the mechanical activity of rat single ventricular myocytes over a wide range of load. To minimize the possible load dependence of sarcoplasmic reticulum Ca2+ loading, contraction mode was switched at every twitch from unloaded shortening to isometric contraction. During a twitch with unloaded shortening, the Ca2+ transients exhibited a higher peak and a higher rate of decay than transients during an isometric twitch. Similarly, when we changed the contraction mode in every pair of twitches, Ca2+ transients were dependent only on the mode of contraction. Mechanical uncoupling with 2,3-butanedione monoxime abolished this dependence on the mode of contraction. Our results suggest that Ca2+ transients reflect the affinity of troponin C for Ca2+, which is influenced by the change in strain on the thin filament but not by the length change per se.

Animals↗
PubMed2003

Measurement of force developed by a single cardiac myocyte using novel carbon fibers.

In order to study the mechanical activity of a single cardiac myocyte under a wide range of load, we have developed a novel force measurement system using carbon fibers. Newly fabricated Graphite Reinforced by Carbon (GRC) fibers greatly facilitate the firm attachment of cell membrane to the fibers. A pair of fibers was attached to both ends of the cell; the rigid fiber as a mechanical ground and the compliant fiber for the strain gauge. By connecting the compliant fiber to the piezoelectric translator and applying the position signal to the driver, we could make the myocyte contract under isometric condition. Feedback control of the system also enabled us to study the relation between work output and the load. This system can be a useful tool in studying the mechanical activity of the cardiac myocyte under genetic as well as pharmacological interventions.

Animals↗
PubMed2003

[Regulatory role of mechanical stress response in cellular function: development of new drugs and tissue engineering].

The investigation of mechanotransduction in the cardiovascular system is essentially important for elucidating the cellular and molecular mechanisms involved in not only the maintenance of hemodynamic homeostasis but also etiology of cardiovascular diseases including arteriosclerosis. The present review summarizes the latest research performed by six academic groups, and presented at the 75th Annual Meeting of the Japanese Pharmacological Society. Technology of cellular biomechanics is also required for research and clinical application of a vascular hybrid tissue responding to pulsatile stress. 1) Vascular tissue engineering: Design of pulsatile stress-responsive scaffold and in vivo vascular wall reconstruction (T. Matsuda); 2) Cellular mechanisms of mechanosensitive calcium transients in vascular endothelium (M. Oike et al.); 3) Cross-talk of stimulation with fluid flow and lysophosphatidic acid in vascular endothelial cells (K. Momose et al.); 4) Mechanotransduction of vascular smooth muscles: Rate-dependent stretch-induced protein phosphorylations and contractile activation (K. Obara et al.); 5) Lipid mediators in vascular myogenic tone (I. Laher et al.); and 6) Caldiomyocyte regulates its mechanical output in response to mechanical load (S. Sugiura et al.).

Animals↗
PubMedDate not supplied

Reduced myocardial flow reserve in anatomically normal coronary arteries due to elevated baseline myocardial blood flow in men with old myocardial infarction.

BACKGROUND: Decreased myocardial flow reserve (MFR) in angiographically normal coronary arteries in patients with old myocardial infarction (OMI) has been reported. METHODS AND RESULTS: To clarify factors for the reduced MFR in OMI and to compare them with those in angina pectoris (AP), baseline myocardial blood flow (MBF) and MBF during dipyridamole administration were measured with nitrogen 13 ammonia positron emission tomography, after which MFR was calculated for 13 men with AP, 18 men with OMI, and 15 age-matched male control subjects. MFR was compared among the 3 groups in segments perfused by nonstenotic arteries. Baseline MBF in patients with OMI was significantly higher than that in patients with AP and control subjects. MBF during dipyridamole administration in patients with OMI was significantly lower than that in control subjects. MFR in patients with AP was 2.50 +/- 0.91 (P <.05 vs control subjects [3.47 +/- 1.25]), and that in patients with OMI was 1.83 +/- 0.61 (P <.01 vs control and AP groups). Ejection fraction (EF) in patients with OMI was significantly decreased compared with that in patients with AP. However, there was no significant difference in the mean score of the individual risk factors between patients with AP and those with OMI. In the pooled data with AP and OMI, baseline MBF and EF were significant for the reduced MFR. CONCLUSIONS: MFR and EF in patients with OMI were significantly decreased compared with those in patients with AP. Increased baseline MBF and decreased EF were significant factors for the reduced MFR in patients with AP and OMI.

Aged↗