Juichiro Shimizu

Electric currents applied during the refractory period can modulate cardiac contractility in vitro and in vivo.

Daniel Burkhoff MD PhD , Itzik Shemer , Bella Felzen , Juichiro Shimizu , Yuval Mika , Marc Dickstein , David Prutchi , Nissim Darvish 3 and Shlomo A. Ben-Haim 2,5 Divisions of Circulatory Physiology and Cardiology, Cardiac Physiology Laboratory, Department of Medicine, Columbia University, N.Y., Impulse Dynamics, Tirat HaCarmel 39120, Israel, Department of Physiology and Biophysics, The Bruce Rappaport Faculty of Medicine, Technion-Israel Institute of Technology, P.O.B. 9649, Haifa 31096, Israel, Department of Anesthesiology, Columbia University, N.Y., Harvard-Thorndike Arrhythmia Institute, Beth-Israel Hospital, 330 Brookline Ave, Boston, Massachusetts 02215, USA

Rescue of Ca2+ overload-induced left ventriclur dysfunction by targeted ablation of phospholamban

In failing hearts, a deficiency in sarco(endo)plasmic reticulum Ca2+ -ATPase (SERCA)2a results in abnormal Ca2+ handling and diminished contraction. In addition, a decrease in the phosphorylation of phospholamban (PLB) has been reported. Gene transfer of antisense PLB (asPLB) can improve contractile function in the failing human myocardium. Gene transfer of SERCA2a improves survival and the energy potential in failing hearts. The aim of present study was to evaluate whether enhancement of SERCA2a function prevents acute Ca2+ overload-induced left ventricular (LV) dysfunction in rat hearts. We ablated PLB using adenoviral gene transfer of asPLB by a new and less invasive gene delivery method, which involved a percutaneous technique. Experiments were performed on 13 excised cross-circulated rat hearts: 5 rats underwent sham operations, 4 rats underwent gene transfer of the reporter gene beta-galactosidase (Ad.beta-gal), and 4 rats underwent gene transfer of asPLB (Ad.asPLB). After clearance of high Ca2+ infused into the coronary, there was LV contractile dysfunction associated with the decreased myocardial O2 consumption per beat (Vo2) intercept (equal to decreased Vo2 for Ca2+ handling in excitation-contraction coupling) of the Vo2-systolic pressure-volume area (PVA; total mechanical energy per beat) linear relation in the hearts that underwent sham operation and had been infected with Ad.beta-gal. Hearts that had been infected with Ad.asPLB were rescued from LV contractile dysfunction associated with an unchanged Vo2 intercept of the Vo2-PVA linear relation. We conclude that SERCA2a function enhanced by adenoviral gene transfer of asPLB prevents Ca2+ overload-induced LV contractile dysfunction in terms of mechanical work and especially energetics.

A new integrative method to quantify total Ca2+ handling and futile Ca2+ cycling in failing hearts

Ca2+ handling in excitation-contraction coupling requires considerable O2 consumption (Vo 2) in cardiac contraction. We have developed an integrative method to quantify total Ca2+ handling in normal hearts. However, its direct application to failing hearts, where futile Ca2+ cycling via the Ca2+-leaky sarcoplasmic reticulum (SR) required an increased Ca2+handling Vo 2, was not legitimate. To quantify total Ca2+ handling even in such failing hearts, we combined futile Ca2+ cycling with Ca2+ handling Vo 2 and the internal Ca2+ recirculation fraction via the SR. We applied this method to the canine heart mechanoenergetics before and after intracoronary ryanodine at nanomolar concentrations. We found that total Ca2+ handling per beat was halved after the ryanodine treatment from ∼60 μmol/kg left ventricle before ryanodine. We also found that futile Ca2+ cycling via the SR increased to >1 cycle/beat after ryanodine from presumably zero before ryanodine. These results support the applicability of the present method to the failing hearts with futile Ca2+ cycling via the SR.

Radio frequency transmyocardial revascularization enhances angiogenesis and causes myocardial denervation in canine model.

Transmyocardial revascularization (TMR) relieves angina and improves exercise tolerance in patients. Angiogenesis and myocardial denervation have been proposed as factors contributing to these benefits. To test whether radio frequency transmyocardial revascularization (RF‐TMR) enhances angiogenesis and causes myocardial denervation.

X-ray Diffraction from a Left Ventricular Wall of Rat Heart

We studied x-ray diffraction from the left ventricular wall of an excised, perfused whole heart of a rat using x rays from the third-generation synchrotron radiation facility, SPring-8. With the beam at right angles to the long axis of the left ventricle, well-oriented, strong equatorial reflections were observed from the epicardium surface. The reflections became vertically split arcs when the beam passed through myocardium deeper in the wall, and rings were observed when the beam passed into the inner myocardium of the wall. These diffraction patterns were explained by employing a layered-spiral model of the arrangement of muscle fibers in the heart. In a quiescent heart with an expanded left ventricle, the muscle fibers at the epicardium surface were found to have a (1,0) lattice spacing smaller than in the rest of the wall. The intensity ratio of the (1,0) and (1,1) equatorial reflections decreased on contraction with a similar time course in all parts of the wall. The results show that it is possible to assign the origin of reflections in a diffraction diagram from a whole heart. This study offers a basis for interpretation of x-ray diffraction from a beating heart under physiologically and pathologically different conditions.

O2 cost of contractility but not of mechanical energy increases with temperature in canine left ventricle

We investigated the effects of myocardial temperature on left ventricular (LV) mechanoenergetics in the excised, cross-circulated canine heart. We used the framework of the LV contractility ( E max)-pressure-volume area (PVA; a measure of total mechanical energy)-myocardial oxygen consumption (Vo 2) relationship. We have shown this framework to be useful to integrative analysis of the mechanoenergetics of a beating heart. In isovolumic contractions at a constant pacing rate, increasing myocardial temperature from 30 to 40°C depressed E max and increased the oxygen cost of E max, which was enhanced by dobutamine, in a linear manner. However, the slope of the Vo 2-PVA relation (reciprocal of contractile efficiency) and its Vo 2intercept remained constant. Q10values of E max, the oxygen cost of E max, and the oxygen cost of PVA were 0.4, 2.1 and 1.0, respectively, around normothermia. We conclude that the temperature-dependent processes of cross-bridge cycling and Ca2+handling integratively depress E max and augment its oxygen cost without affecting the oxygen cost of PVA as myocardial temperature increases by 10°C around normothermia.We investigated the effects of myocardial temperature on left ventricular (LV) mechanoenergetics in the excised, cross-circulated canine heart. We used the framework of the LV contractility (E(max))-pressure-volume area (PVA; a measure of total mechanical energy)-myocardial oxygen consumption (VO(2)) relationship. We have shown this framework to be useful to integrative analysis of the mechanoenergetics of a beating heart. In isovolumic contractions at a constant pacing rate, increasing myocardial temperature from 30 to 40 degrees C depressed E(max) and increased the oxygen cost of E(max), which was enhanced by dobutamine, in a linear manner. However, the slope of the VO(2)-PVA relation (reciprocal of contractile efficiency) and its VO(2) intercept remained constant. Q(10) values of E(max), the oxygen cost of E(max), and the oxygen cost of PVA were 0.4, 2.1 and 1.0, respectively, around normothermia. We conclude that the temperature-dependent processes of cross-bridge cycling and Ca(2+) handling integratively depress E(max) and augment its oxygen cost without affecting the oxygen cost of PVA as myocardial temperature increases by 10 degrees C around normothermia.

A new possibility for repairing the anal dysfunction by promoting regeneration of the reflex pathways in the enteric nervous system

Moderate rectal distension elicits recto-rectal reflex contractions and simultaneous recto-internal anal sphincter reflex relaxations that together comprise the defecation reflex. Both reflexes are controlled by 1) pelvic nerves, 2) lumbar colonic nerves, and 3) enteric nervous system. The aim of the present study was to explore a novel approach to repairing the defecation reflex dysfunction by using the plasticity of enteric nervous pathways. Experiments were performed in anesthetized guinea pigs with ethyl carbamate. The rectum 30 mm oral from the anal verge was transected without damage to extrinsic nerves, and subsequent end-to-end one-layer anastomosis was performed. Recovery of the defecation reflex and associated reflex pathways were evaluated. Eight weeks after sectioning of intrinsic reflex nerve pathways in the rectum, the defecation reflex recovered to the control level, accompanied with regeneration of reflex pathways. The 5-HT(4)-receptor agonist mosapride (0.5 and 1.0 mg/kg) significantly (P < 0.01) enhanced the recovered defecation reflex 8 wk after surgery. Two weeks after local treatment with brain-derived neurotrophic factor (BDNF: 10(-6) g/ml) at the rectal anastomotic site, the recto-internal anal sphincter reflex relaxations recovered and some bundles of fine nerve fibers were shown to interconnect the oral and anal ends of the myenteric plexus. These results suggested a possibility for repairing the anal dysfunction by promoting regeneration of the reflex pathways in the enteric nervous system with local application of BDNF.

Logistic character of myocardial twitch force curve : simulation

SummaryWe found that the isovolumic pressure-time curve of the canine left ventricle closely fitted the difference of two logistic function curves and that the isovolumic relaxation-pressure curve segment was more reliably characterized by a logistic time constant than by the conventional exponential time constant. We therefore hypothesized that the calcium (Ca) transient and the Ca-troponin (Tn) binding and crossbridge (CB) kinetics underlay the logistic character of the ventricular isovolumic pressure curve. We tested this hypothesis with a computer simulation of a simple Ca and CB kinetics model of myocardial isometric twitch force development. We assumed the isometric force curve (F) to be proportional to the instantaneous number of attached CBs that was theoretically given as the difference between the cumulative CB attachment and detachment curves. We radically changed the Ca transient, Ca-Tn binding, and CB kinetic parameters. We always found that both the cumulative CB attachment and detachment curves closely fitted logistic functions. The difference curve of these two best-fit logistic functions closely fitted the theoretical F curve with certain combinations of the Ca transient, the Ca-Tn binding, and the CB kinetic parameters. These results seem to support our hypothesis.

Starling-effect-independent lusitropism index in canine left ventricle: logistic time constant.

The logistic time constant (&tgr;L) has been proposed as a better index of the rate of left ventricular (LV) relaxation or lusitropism than the conventional monoexponential time constant (&tgr;E). However, whether and how the Frank-Starling effect influences &tgr;L remains to be elucidated. We compared the effect of LV volume (LVV) loading on both logistic and monoexponential fittings. The isovolumic LV relaxation pressure curves from the maximum negative time derivative of pressure (-dP/dtmax) were analyzed at 3 different end-points at 4 LVVs of 10, 12, 14, and 16 mL in 8 excised, cross-circulated canine hearts. We found that the logistic fitting was superior to the monoexponential fitting at all LVVs and end-points. LVV loading did not affect &tgr;L but affected &tgr;E slightly. Although the advancing end-point increased both &tgr;L and &tgr;E, the increases were significantly smaller for &tgr;L than for &tgr;E at all LVVs. Moreover, the changes in both the amplitude constants and nonzero asymptotes with the advancing end-point were significantly smaller for the logistic fitting than for the monoexponential fitting. We conclude that &tgr;L served as a more reliable index of lusitropism that is independent of the change in LVV loading or the Frank-Starling effect.

Evaluation of micromotion of vascular endothelial cells in electrical cell-substrate impedance sensing (ECIS) method using a mathematical model

We proposed a mathematical model for the microdynamics of cultured cells measured with ECIS (Electrical Cell-substrate Impedance Sensing) system that can separately evaluate cell-to-cell and cell-to-substrate gaps. Our mathematical model is composed of culture medium impedance between cells (Zsol), cell impedance (Zc), and polarization impedance of the electrode (Zp). Zsol consists of the resistance between cells (Rsol) and the capacitance between cells (Csol) of the culture medium. In particular, Rsol is the resistance component related to the cell-to-cell distance (A). Zc consists of capacitance of the cell membrane (Cc) and resistance of the cell membrane (Rc). Zp depends on the cell-to-substrate distance (h) because of the shielding effect of cells to the electrode. The shielding effect is defined as shielding coefficient (Sk). We examined the changes in the impedance of the electrode without or with cells in various conditions. The electrical characteristics of the electrode with or without cells agreed well with those measured in ECIS system. It was found that whether A or h caused the changes in the impedance could be determined based on the changes in the total resistance and reactance (capacitance); A mainly affects the total resistance value, and h mainly affects total capacitance value. Therefore, we can simply estimate the changes in cell-to-cell and cell-to-substrate gaps with measured total resistance and reactance (capacitance). Based on these results, when the cultured endothelial cells (HUVEC) were stimulated with estrogen for 40 hours, it was proved that the cell-to-cell distances decreased, even though the cell-to-electrode distances slightly increased. This result suggests that the barrier function of endothelium is fortified by estrogen.