Taketo Tanigawa

Altered interaction of FKBP12.6 with ryanodine receptor as a cause of abnormal Ca2+ release in heart failure

OBJECTIVE Little information is available as to the Ca(2+) release function of the sarcoplasmic reticulum (SR) in heart failure. We assessed whether the alteration in this function in heart failure is related to a change in the role of FK binding protein (FKBP), which is tightly coupled with the cardiac ryanodine receptor (RyR) and recently identified as a modulatory protein acting to stabilize the gating function of RyR. METHODS SR vesicles were isolated from dog LV muscles [normal (N), n=6; heart failure induced by 3-weeks pacing (HF), n=6]. The time course of the SR Ca(2+) release was continuously monitored using a stopped-flow apparatus, and [3H]ryanodine-binding and [3H]dihydro-FK506-binding assays were also performed. RESULTS FK506, which specifically binds to FKBP12.6 and dissociates it from RyR, decreased the polylysine-induced enhancement of [3H]ryanodine-binding by 38% in N (P<0.05) but it had no effect in HF. In HF, the rate constant for the polylysine-induced Ca(2+) release from the SR was 61% smaller than in N. FK506 decreased the rate constant for the polylysine-induced Ca(2+) release by 67% in N (P<0.05) but had no effect in HF. The [3H]dihydro-FK506-binding assay revealed that the number (B(max)) of FKBPs was decreased by 83% in HF (P<0.05), while the K(d) value was unchanged. FK506 did not significantly change SR Ca(2+.)-ATPase activity in either N or HF. CONCLUSIONS In HF, the number of FKBPs showed a tremendous decrease; this may underlie the RyR-channel instability and the impairment of the Ca(2+) release function of RyR seen in the failing heart.

Abnormal Ca2+ release from cardiac sarcoplasmic reticulum in tachycardia-induced heart failure

OBJECTIVE In heart failure, little information is available as to the Ca2+ release function of sarcoplasmic reticulum (SR), which plays a major role in cardiac contractile function. Here, we assessed the rapid kinetics of drug-induced Ca2+ release from cardiac SR in combination with a measurement of ryanodine binding in heart failure. METHODS The SR vesicles were isolated from dog left ventricular (LV) muscles (normal (N), n = 10; pacing induced heart failure (HF), n = 10). The time course of SR Ca2+ release was continuously monitored by a stopped-flow apparatus using arsenazoIII as a Ca2+ indicator, and Ca2+ uptake and [3H]ryanodine binding assays were done using a filtration method. RESULTS The amount of Ca2+ uptake was reduced in HF to 55% of N (P < 0.05). Even the more marked and earlier appeared decrease was seen in the rate constant and the initial rate of polylysine (PL; a specific release trigger)-induced Ca2+ release (P < 0.05). However, the PL concentration dependency of the initial rate shifted towards lower concentrations of PL in HF than in N ([PL] at half maximum stimulation = 0.13 vs. 0.35 microM). The [3H]ryanodine binding assay revealed a lower Bmax (pmol/mg) in HF than in N (0.91 +/- 0.19 vs. 2.64 +/- 0.59, P < 0.05), but no difference in Kd (nM) (0.95 +/- 0.29 vs. 0.90 +/- 0.11, P = n.s.). The [PL] dependency on the enhancement of [3H]ryanodine binding again showed a shift towards lower [PL] in HF than in N. CONCLUSIONS In pacing-induced heart failure, the Ca2+ releasing function of SR is disturbed, which may result in an intra-cellular Ca2+ transient that was slowed down.

Dose-dependent effect of ANG II-receptor antagonist on myocyte remodeling in rat cardiac hypertrophy

The goal of this study was to examine the effect of an angiotensin II type 1 (AT1)-receptor antagonist (TCV-116) on left ventricular (LV) geometry and function during the development of pressure-overload LV hypertrophy. A low (LD; 0.3 mg ⋅ kg-1 ⋅ day-1) or a high (HD; 3.0 mg ⋅ kg-1 ⋅ day-1) dose of TCV-116 was administered to abdominal aortic-banded rats over 4 wk, and hemodynamics and morphology were then evaluated. In both LD and HD groups, peak LV pressures were decreased to a similar extent compared with the vehicle-treated group but stayed at higher levels than in the sham-operated group. In the LD group, both end-diastolic wall thickness (3.08 ± 0.14 mm) and myocyte width (13.3 ± 0.1 μm) decreased compared with those in the vehicle-treated group (3.67 ± 0.19 mm and 15.3 ± 0.1 μm, respectively; both P < 0.05). In the HD group, myocyte length was further decreased (HD: 82.6 ± 2.6, LD: 94.1 ± 2.9 μm; P < 0.05) in association with a reduction in LV midwall radius (HD: 3.36 ± 0.12, LD: 3.60 ± 0.14 mm; P < 0.05) and peak midwall fiber stress (HD: 69 ± 8, LD: 83 ± 10 × 103dyn/cm2; P < 0.05). There was no significant difference in cardiac output among all groups. The AT1-receptor antagonist TCV-116 induced an inhibition of the development of pressure-overload hypertrophy. Morphologically, not only the width but also the length of myocytes was attenuated with TCV-116, leading to a reduction of midwall radius and hence wall stress, which in turn may contribute to a preservation of cardiac output.The goal of this study was to examine the effect of an angiotensin II type 1 (AT1)-receptor antagonist (TCV-116) on left ventricular (LV) geometry and function during the development of pressure-overload LV hypertrophy. A low (LD; 0.3 mg x kg(-1) x day(-1)) or a high (HD; 3.0 mg x kg(-1) x day(-1)) dose of TCV-116 was administered to abdominal aortic-banded rats over 4 wk, and hemodynamics and morphology were then evaluated. In both LD and HD groups, peak LV pressures were decreased to a similar extent compared with the vehicle-treated group but stayed at higher levels than in the sham-operated group. In the LD group, both end-diastolic wall thickness (3.08 +/- 0.14 mm) and myocyte width (13.3 +/- 0.1 microm) decreased compared with those in the vehicle-treated group (3.67 +/- 0.19 mm and 15.3 +/- 0.1 microm, respectively; both P < 0.05). In the HD group, myocyte length was further decreased (HD: 82.6 +/- 2.6, LD: 94.1 +/- 2.9 microm; P < 0.05) in association with a reduction in LV midwall radius (HD: 3.36 +/- 0.12, LD: 3.60 +/- 0.14 mm; P < 0.05) and peak midwall fiber stress (HD: 69 +/- 8, LD: 83 +/- 10 x 10(3) dyn/cm2; P < 0.05). There was no significant difference in cardiac output among all groups. The AT1-receptor antagonist TCV-116 induced an inhibition of the development of pressure-overload hypertrophy. Morphologically, not only the width but also the length of myocytes was attenuated with TCV-116, leading to a reduction of midwall radius and hence wall stress, which in turn may contribute to a preservation of cardiac output.

Polylysine-induced rapid Ca2+ release from cardiac sarcoplasmic reticulum.

The rapid kinetics of polylysine-induced Ca2+ release from cardiac sarcoplasmic reticulum (SR) was assessed in combination with its effect on ryanodine binding. SR vesicles were isolated from canine cardiac SR. The time course of SR Ca2+ release was continuously monitored by a stopped-flow apparatus, and [3H]ryanodine binding was done by using the filtration method. The initial rate of polylysine-induced Ca2+ release from cardiac SR revealed different concentration dependence from those observed in skeletal SR. The initial rate peaked at 0.11 microM, followed by a decrease at higher concentrations in skeletal SR, whereas it increased to 3.7 microM in cardiac SR. The [3H]ryanodine binding was also stimulated by polylysine with an identical parallelism with Ca2+ release in terms of polylysine concentration dependence. Thus we demonstrated that the cardiac SR Ca2+ release channel is sensitive to activation by polylysine and that there is a difference in the concentration dependence of polylysine-induced activation of cardiac and skeletal SR Ca2+ release channels.

Usefulness of free-angle M-mode echocardiography in assessing left ventricular dimension and left ventricular systolic function

ObjectivesTo assess the usefulness of free-angle M-mode echocardiography in measuring left ventricular (LV) dimension and global systolic function.BackgroundThe validity of conventional M-mode echocardiography in assessing LV dimension and global systolic function is well known; the incidental angle between the M-mode cursor and true LV minor axis diameter, however is a potential cause of measurement error. Free-angle M-mode echocardiography may overcome the limitation of M-mode cursor arrangement in conventional M-mode echocardiography.MethodsThirteen normal volunteers and 10 patients in whom abnormal left ventricular wall motion was not detected by echocardiography (mean age, 53±17 years) were enrolled in this study. Conventional and free-angle M-mode echocardiographic images of the LV were obtained by echocardiography (ALOKA SSD-5500) using a 2.5-MHz transducer, and the LV end-diastolic (LVDd) and end-systolic (LVDs) dimensions were measured by the leading edge method. LV end-diastolic and end-systolic volumes were calculated using a formula by Teichholz, and the LV ejection fraction (LVEF) was obtained. Data from conventional M-mode echocardiography and free-angle M-mode echocardiography were then compared.ResultsMeasurements obtained with conventional M-mode and free-angle M-mode echocaardiography were strongly correlated. Correlation coefficients for LVDd, LVDs, and LVEF were 0.98, 0.98, and 0.96, respectively (p<0.001 in each case).ConclusionsAssessment of left ventricular dimension, and global systolic function with free-angle M-mode can be as accurate as conventional M-mode in subjects in whom left ventricular wall motion abnormality is not detectable by echocardiogram. Moreover, when there is improper M-mode cursor direction in conventional echocardiography, free-angle M-mode echocardiography can assess global left ventricular systolic function more accurately and conveniently than conventional M-mode echocardiography.

Effects of balanced vasodilator, flosequinan, on aortic impedance in failing heart

An arteriovenous vasodilator, flosequinan, has been shown to be effective for the treatment of acute heart failure. However, little is known as to its effect on aortic impedance, which is known to be a proper and precise expression of left ventricular (LV) afterload. To evaluate the acute cardiovascular effect of flosequinan in failing heart, we administered flosequinan intravenously to seven dogs with cardiac failure produced by an infusion of carbon powder (20-50 microm in diameter) into left main trunks of coronary artery. The LV-pump function was severely impaired after intracoronary injection of carbon powder, as evidenced by the findings that cardiac output, circumferential shortening velocity (mean Vcf), and peak +dP/dt of LV pressure were all decreased, associated with a significant increase in LV end-diastolic pressure. Flosequinan (0.9 mg/kg, i.v.) increased cardiac output by 28%, mean Vcf by 44%, and peak +dP/dt by 24%, whereas it decreased total systemic resistance by 32%, time constant of LV pressure decay by 22%, and LV end-diastolic pressure by 18%. Moreover, flosequinan substantially decreased the pulsatile components of LV afterload (i.e., characteristic impedance by 11% and arterial wave reflection coefficient by 45%). Thus flosequinan exerted not only positive inotropic but also positive lusitropic effects, in association with a significant reduction of both pulsatile and steady components of LV afterload, contributing to an improvement of LV-pump function in acute cardiac failure.