Naoshi Kobayakawa

Comparison of Unitary Displacements and Forces Between 2 Cardiac Myosin Isoforms by the Optical Trap Technique: Molecular Basis for Cardiac Adaptation

To provide information on the mechanism of cardiac adaptation at the molecular level, we compared the unitary displacements and forces between the 2 rat cardiac myosin isoforms, V1 and V3. A fluorescently labeled actin filament, with a polystyrene bead attached, was caught by an optical trap and brought close to a glass surface sparsely coated with either of the 2 isoforms, so that the actin-myosin interaction took place in the presence of a low concentration of ATP (0.5 micromol/L). Discrete displacement events were recorded with a low trap stiffness (0.03 to 0.06 pN/nm). Frequency distribution of the amplitude of the displacements consisted of 2 gaussian curves with peaks at 9 to 10 and 18 to 20 nm for both V1 and V3, suggesting that 9 to 10 nm is the unitary displacement for both isoforms. The duration of the displacement events was longer for V3 than for V1. On the other hand, discrete force transients were recorded with a high trap stiffness (2.1 pN/nm), and their amplitude showed a broad distribution with mean values between 1 and 2 pN for V1 and V3. The durations of the force transients were also longer for V3 than for V1. These results indicate that both the unitary displacements and forces are similar in amplitude but different in duration between the 2 cardiac myosin isoforms, being consistent with the reports that the tension cost is higher in muscles consisting mainly of V1 than those consisting mainly of V3.

Improvement of Impaired Myocardial Vasodilatation Due to Diffuse Coronary Atherosclerosis in Hypercholesterolemics After Lipid-Lowering Therapy

BACKGROUND Diminished myocardial vasodilatation (MVD) in hypercholesterolemics without overt coronary stenosis has been reported. However, whether the diminished MVD of angiographically normal coronary arteries in hypercholesterolemics can be reversed after lipid-lowering therapy is not known. METHODS AND RESULTS A total of 27 hypercholesterolemics and 16 age-matched controls were studied. All patients had >1 normal coronary artery, and those segments that were perfused by anatomically normal coronary arteries were studied. Myocardial blood flow (MBF) was measured during dipyridamole loading and at baseline using positron emission tomography and 13N-ammonia, after which MVD was calculated before and after lipid-lowering therapy. Total cholesterol was significantly higher in hypercholesterolemics (263+/-33.8) than in controls (195+/-16.6), and it normalized after lipid-lowering therapy (197+/-19.9). Baseline MBF (ml. min-1. 100 g-1) was comparable among hypercholesterolemics (both before and after therapy) and controls. MBF during dipyridamole loading was significantly lower in hypercholesterolemics before therapy (189+/-75.4) than in controls (299+/-162, P<0.01). However, MBF during dipyridamole loading significantly increased after therapy (226+/-84.7; P<0.01). MVD significantly improved after therapy in hypercholesterolemics (2.77+/-1.35 after treatment [P<0.05] versus 2. 02+/-0.68 before treatment [P<0.01]), but it remained significantly higher in controls (3.69+/-1.13, P<0.01). There was a significant relationship between the percent change of total cholesterol and the percent change of MVD before and after lipid-lowering therapy (r=-0. 61, P<0.05). CONCLUSIONS Diminished MVD of anatomically normal coronary arteries in hypercholesterolemics can be reversed after lipid-lowering therapy.

Altered Myocardial Vasodilatation in Patients With Hypertriglyceridemia in Anatomically Normal Coronary Arteries

Reduced myocardial vasodilatation (MVD) in hypercholesterolemics without overt coronary stenosis has been reported. However, the status of MVD in hypertriglyceridemics has not yet been clarified. The aim of this study was to investigate whether MVD is impaired in patients with hypertriglyceridemia without overt coronary stenosis. Twenty-three hypertriglyceridemics (10 normocholesterolemic hypertriglyceridemics [HTGs] and 13 mixed combined hyperlipidemics [MCHLs]) and 13 age-matched controls were studied. All patients were proven to have more than one normal coronary artery, as diagnosed by coronary angiography, and those segments that were perfused by anatomically normal coronary arteries were used in the study. Myocardial blood flow (MBF) during dipyridamole (DP) loading and baseline MBF were measured by using positron emission tomography and [13N]ammonia, after which MVD was calculated. Baseline MBF (mL.min(-1).100 g(-1)) was comparable among HTG (76.0+/-26.1), MCHL (77.0+/-26.1), and controls (80.3+/-38.5). However, MBF during DP loading was significantly lower in MCHL (159+/-52.5) than in control subjects (292+/-166, P<.01), while it was comparable in HTG (202+/-104) and controls. MVD was significantly reduced in both HTG (2.70+/-1.09, P<.05) and MCHL (2.07+/-.70, P<.01) compared with controls (3.73+/-1.14). MVD in MCHLs tended to be reduced compared with that in HTGs, but the difference was statistically insignificant (P=.08). There was a significant relationship between MVD and both plasma triglycerides (r=-.47, P<.01) and plasma total cholesterol (r=-.55, P<.01). When controls and HTGs were combined, the relationship between MVD and plasma total triglycerides became more prominent (r=-.55, P<.05), and the significant relationship between cholesterol level and MVD disappeared. Multivariate regression analysis has revealed that the triglyceride level (F=5.2, P<.05) was independently related to MVD (r=.69, P<.01). In conclusion, MVD was reduced in hypertriglyceridemics in anatomically normal coronary arteries. Hypertriglyceridemia is an independent factor for this abnormality.

Inhibition of Carnitine Synthesis Protects Against Left Ventricular Dysfunction in Rats with Myocardial Ischemia

During myocardial ischemia, inhibition of the carnitine-mediated transportation of fatty acid may be beneficial because it facilitates glucose utilization and prevents an accumulation of fatty acid metabolites. We orally administered 3-(2,2,2-trimethyl hydrazinium) propionate (MET), an inhibitor of carnitine synthesis, for 20 days to rats. Then we evaluated left ventricular (LV) function during brief ischemia by using a buffer-perfused isovolumic heart model. After 15 min of reoxygenation after the transient ischemia, LV peak systolic pressure (PSP) almost completely returned to the baseline level in rats given MET (96 +/- 4%), whereas it was only partially (77 +/- 16%) recovered in the placebo-treated rats. We induced myocardial infarction in other rats by ligating the left anterior descending coronary artery. Then the animals were given MET for 20 days, and LV function was compared. In the placebo-treated rats (with myocardial infarction, but without drug treatment), LVPSP was lower than that in the sham group [108 +/- 19 (n = 10) vs. 136 +/- 15 mm Hg (n = 13); p < 0.05], and the time constant (T) of LV pressure decay was elongated (36 +/- 4 vs. 30 +/- 7 ms; p < 0.05). In MET-treated groups, however, neither PSP nor T differed from those in the sham group. In conclusion, inhibition of the carnitine-mediated transportation of fatty acid by MET protected against left ventricular dysfunction in acute and chronic myocardial ischemia.

Different cardiac myosin isoforms exhibit equal force-generating ability in vitro

We measured forces generated by myosin molecules and a single actin filament using an optical trap system. The force per unit length of actin filament did not differ significantly between cardiac myosin isoforms. V1 and V3. This indicates that the ability to generate force is equal between V1 and V3, despite their difference in the unloaded sliding velocity past actin.

A Case of Transient 2:1 Atrioventricular Block, Resolved by Thyroxine Supplementation for Subclinical Hypothyroidism

A 42‐year‐old man was admitted to our hospital with palpitation attacks. Holter ECG showed 2:1 atrioventricular block and bradycardia with the minimum heart rate of 44 beats/min. There was a possible indication of electrophysiological study and cardiac pacemaker implantation. Laboratory data on admission revealed elevated thyrotropin level, with normal thyroxine level. To rule out functional atrioventricular block, we tried 2 weeks of the thyroxine supplementation, and Holter ECG showed improved heart rate without any atrioventricular block or long pause. We experienced that subclinical hypothyroidism caused severe bradycardia and 2:1 atrioventricular block, and that thyroxine supplementation completely improved these conditions.

Distinct kinetic properties of cardiac myosin isoforms revealed by in vitro studies.

To clarify the physiological significance of myosin isoform redistribution in cardiac adaptation process, we compared the kinetic property of the two cardiac myosin isoforms using in vitro motility assay techniques. Cardiac myosin isoforms V1 and V3 were obtained from ventricular muscle of young rats and hypothyroid rats respectively. On each of these myosin isoforms fixed on a glass coverslip, fluorescently labeled actin filaments were made to slide in the presence of ATP. To measure the force generated by actomyosin interaction, a small latex bead was attached to the barbed end of an actin filament and the bead was captured by the laser optical trap installed in a microscope. The force was determined from the distance between the bead and the trap positions under either auxotonic or isometric conditions. The time-averaged force generated by multiple cross-bridges did not differ significantly between the two isoforms. On the other hand, the unitary force measurement revealed the same level of amplitude but a longer duration for V3 isoform. The same level of time-averaged force is in agreement with not only our previous finding but the results of maximum force measurement in muscle preparations. The difference in kinetic characteristics of the two isoforms could account for the difference in economy of force development and the basis for cardiac adaptation mechanism.

A Case of Severe Diabetes Mellitus Occurred During Management of Heart Failure with Carvedilol and Furosemide

Carvedilol, which also has alpha-adrenoceptor antagonistic and vasodilating actions, is a unique betaadrenoceptor antagonist. One of its specific features is that carvedilol hardly impairs glucose metabolism [1,2]. However, we recently experienced a case of acute onset or severe exacerbation of diabetes mellitus (DM) during carvedilol therapy in conjunction with loop diuretics, furosemide for dilated cardiomyopathy (DCM). A 37-year-old man came to our hospital with exertional dyspnea and pretibial edema in April 2000. His height was 171 cm and weight was 93 kg with body mass index of 31.8 kg/m2. Physiological examinations revealed no substantial abnormality except mild moist rale in bilateral lower lung fields. The chest X-ray showed pulmonary congestion and the ECG showed sinus tachycardia. Echocardiography revealed diffuse hypokinetic left ventricle (LV) with LV end-diastolic dimension of 61 mm, LV end-systolic dimension of 51 mm and LV ejection fraction of 42%. Coronary angiography showed normal coronary arteries. We diagnosed him as DCM based on these findings. Furosemide 40 mg/day, spironolactone 50 mg/day and candesartan 4 mg/day were started. His blood HbA1c level at outpatient visit in October 2000 was 4.9%. Approximately one year later, in May 2001, we introduced the betablockade therapy with carvedilol at maintenance dose of 10 mg/day. At this point, his blood HbA1c level was 5.1%. In January 2002, he started to feel extreme thirsty and to drink more than a litter of water a day. He had lost 10 kg in 3 months. There had been no severe clinical events of viral infection or pancreatitis. At his clinic visit on March 22nd, 2002, his blood sugar level was 557 mg/dl, HbA1C level was 17.4%, serum cholesterol level was 326 mg/dl, and triglyceride level was 145 mg/dl. Other laboratory findings include serum creatinine 1.5 mg/dl, BUN 16 mg/dl, Na 127 mEq/l, and K 3.7 mEq/l. His serum anti-GAD antibody was below 0.3 (negative). First, we stopped furosemide as of March 23rd, 2002. His fasting blood sugar level went down to 160 mg/dl a week later. Then, we replaced carvedilol with 20 mg of metoprolol on April 1st, 2002. After 2 weeks, his fasting blood sugar level further decreased to 106 mg/dl and urine sugar went down to 1.6 g/day, both of which have been stable thereafter with the same medications. Incidence of carvedilol-induced hyperglycemia was known to be rare and mild [1,2]. Mechanisms of the carvedilol-induced hyperglycemia are not known, although alpha-blocking effects on pancreas may impair insulin secretion [3]. Special conditions in this case was the preceding administration of furosemide which may have decreased peripheral circulation and increased insulin resistance. He also may have mildly impaired glucose tolerance before the furosemide and carvedilol administration. Although carvedilol only rarely causes hyperglycemia, its possibility should never be neglected especially when diuretics are given in a patient with impaired glucose tolerance.

Pretreatments with a novel pure potassium channel blocker, Nifekalant, were effective in the electrical atrial defibrillation: a report of two cases.

Atrial fibrillation is a common cardiac arrhythmia often associated with hemodynamic impairment and thromboembolic events. The direct-current (DC) shock cardioversion is an established therapeutic strategy especially for new-onset atrial fibrillation with hemodynamic instability or unacceptable symptoms [1]. However, it fails in many cases without obtaining even a single sinus beat. Although many antiarrhythmic drugs were reported to possibly enhance DC shock conversion, their clinical application is still controversial with substantial adverse effects, such as paradoxical increase in the defibrillation threshold [2]. Nifekalant hydrochloride (NIF) is an almost specific blocker of rapid component of the delayed rectifier potassium current (Ikr) [3]. It does not inhibit sodium channels or β-adrenergic receptors. The drug is known by effectiveness for variety of ventricular tachyarrhythmia. Here we report two cases with refractory atrial fibrillations that were successfully defibrillated by the DC shocks in combination with a NIF pretreatment.