Effects of azumolene on arrhythmia substrate in a model of recurrent long-duration ventricular fibrillation.

BACKGROUND: Proarrhythmic risk of conventional anti-arrhythmic agents is linked to unintended modulation of membrane voltage dynamics. We have demonstrated that the anti-fibrillatory effect of azumolene is mediated via stabilization of the hyperphosphorylated ryanodine receptor (RyR2), leading to attenuation of diastolic calcium leak. However, the concomitant effects on membrane voltage dynamics have not been evaluated yet. METHODS: After baseline optical mapping, Langendorff-perfused rabbit hearts treated with azumolene, or vehicle, were subjected to global ischemia-reperfusion (I/R) followed by two episodes of long-duration ventricular fibrillation (LDVF). Simultaneous dual epicardial calcium transient (CaT) and voltage dynamics were studied optically. RESULTS: Pre-treatment with azumolene was associated with higher CaT amplitude alternans ratios (0.94 ± 0.02 vs. 0.78 ± 0.03 in control hearts, at 6 Hz; p = 0.005; and action potential amplitude alternans ratio (0.95 ± 0.02 vs. 0.78 ± 0.04 at 6.0 Hz; p = 0.02), and reduction of action potential duration (APD80) dispersion (9.0 ± 4.8 msec vs. 19.3 ± 6.6 msec at 6.0 Hz p = 0.02) and optical action potential upstroke rise time (26.3 ± 2.6 msec in control vs. 13.8 ± 0.6 msec at 6.0 Hz, p = 0.02) after LDVF. No change in action potential duration (APD) was noted with azumolene treatment. CONCLUSION: In a model of ischemic recurrent LDVF, treatment with azumolene led to reduction of cardiac alternans, i.e., calcium and voltage alternans. Unlike conventional anti-arrhythmic agents, reduction of action potential upstroke rise time and preservation of action potential duration following azumolene treatment may reduce the proarrhythmia risk.

Essential role of ryanodine receptor 2 phosphorylation in the effect of azumolene on ventricular arrhythmia vulnerability in a rabbit heart model.

INTRODUCTION: Following long-duration ventricular fibrillation (LDVF), reinitiation of ventricular fibrillation (VF) poses a major challenge during resuscitation. Ryanodine receptor 2 (RyR2) becomes dysfunctional following VF. The relationship between LDVF, RyR2 modulation, and ventricular refibrillation, as well as the role of RyR2 phosphorylation, remains unknown. METHODS: Langendorff-perfused rabbit hearts were subjected to global ischemia and treated with azumolene (or vehicle alone in controls) upon reperfusion. After electrical induction of an initial LDVF episode, each heart was further stimulated electrically to assess reinducibility of VF. Myocardial calcium dynamics were assessed by optical mapping. RyR2 phosphorylation in left ventricular tissue extracts was analyzed by Western blot analysis. RESULTS: Fewer episodes of refibrillation (lasting ≥ 10 seconds) were induced in azumolene-treated hearts than in controls (P = 0.01); however, this reduction in refibrillation was abrogated in the presence of the protein kinase A inhibitor H89. Spontaneous calcium elevation was significantly lower in azumolene-treated hearts than in control hearts ( P = 0.002) and in hearts pretreated with H89 before azumolene ( P = 0.01). RyR2 phosphorylation at Ser2808 was higher in hearts subjected to LDVF than in non-VF hearts ( P = 0.029), while no significant difference was found at Ser2814. Pretreatment with H89 led to significantly less RyR2 phosphorylation at Ser2808 ( P = 0.04) after LDVF, while pretreatment with KN93 or azumolene alone showed no effects on RyR2 phosphorylation. CONCLUSION: Ventricular refibrillation following LDVF was reduced by azumolene, which also improves calcium dynamics. RyR2 phosphorylation at Ser2808 is a prerequisite for the beneficial effects of azumolene.

Synchronizing systolic calcium release with azumolene in an experimental model.

Background: Post-defibrillation myocardial contractile dysfunction adversely affects the survival of patients after cardiac arrest. Attenuation of diastolic calcium (Ca2+) overload by stabilization of the cardiac ryanodine receptor (RyR2) is found to reduce refibrillation after long-duration ventricular fibrillation (LDVF). Objective: In the present study, we explored the effects of RyR2 stabilization by azumolene on systolic Ca2+ release synchrony and myocardial contractility. Methods: After completion of baseline optical mapping, Langendorff-perfused rabbit hearts were subjected to global ischemia followed by reperfusion with azumolene or deionized distilled water (vehicle). Following reperfusion, LDVF was induced with burst pacing. In the first series of experiments (n = 16), epicardial Ca2+ transient was analyzed for Ca2+ transient amplitude alternans and dispersion of Ca2+ transient amplitude alternans index (CAAI). In the second series of experiments following the same protocol (n = 12), ventricular contractility was assessed by measuring the left ventricular pressure. Results: Ischemic LDVF led to greater CAAI (0.06 ± 0.02 at baseline vs 0.12 ± 0.02 post-LDVF, P < .01) and magnitude of dispersion of CAAI (0.04 ± 0.01 vs 0.09 ± 0.01, P < .01) in control hearts. In azumolene-treated hearts, no significant changes in CAAI (0.05 ± 0.01 vs 0.05 ± 0.01, P = .84) and dispersion of CAAI (0.04 ± 0.01 vs 0.04 ± 0.01, P = .99) were noted following ischemic LDVF. Ischemic LDVF was associated with reduction in left ventricular developed pressure (100% vs 36.8% ± 6.1%, P = .002) and dP/dtmax (100% vs 45.3% ± 6.5%, P = .003) in control hearts, but these reductions were mitigated (left ventricular developed pressure: 100% vs 74.0% ± 8.1%, P = .052, dP/dtmax: 100% vs 80.8% ± 7.9%, P = .09) in azumolene-treated hearts. Conclusion: Treatment with azumolene is associated with improvement of systolic Ca2+ release synchrony and myocardial contractility following ischemic LDVF.

The Effects of Azumolene and Dantrolene on Diaphragm Muscle in Rabbit / 中国医师杂志

azumolene. Conclusion The muscle- relaxing effects of azumolene on diaphragm appeared to be approximately similar to those of dantrolene. The characteristics of action of azumolene and dantrolene were significantly different from those of pancuronium.

notropic and Electrophysiologic Effect of Azumolene in Intact Myocardium In Vitro / 대한마취과학회지

BACKGROUND: The effects of various concentrations (10, 25 micrometer) of azumolene, an analogue of dantrolene, were studied in isolated guinea pig ventricular papillary muscles by measuring the effects on myocardial contractility and electrophysiologic parameters. METHODS: Isometric forces were studied in normal and 26 mM K Tyrode's solution. Rapid cooling contracture, an index of SR Ca2 content, was performed. Normal and slow action potentials (APs) were evaluated by using conventional microelectrode technique. RESULTS: Ten and 25 micrometer azumolene depressed peak force and maximum rate of force development ( 30 40%). Dose-dependent depression was shown at 2 and 3 Hz stimulation rate. Rapid cooling contractures following 10 and 25 micrometer azumolene was not altered compared to control while peak force at 2 Hz stimulation rate just prior to cooling was depressed similarly to normal Tyrode's solution. In 26 mM K Tyrode's solution, 10 and 25 micrometer azumolene caused depression of early (10 micrometer: 20%) and late (10 micrometer: 50%) force development. In slow APs, shortening of AP duration at 20, 50, and 90% of the repolarization phase, as well as a small but significant reduction of dV/dt-max ( 20%) were shown at 0.25 Hz stimulation rate. There was no alteration in AP parameters in normal APs. CONCLUSIONS: The direct myocardial depressant action of azumolene seems to be at least in part caused by inhibition of Ca2 influx via the Ca2 channel in sarcolemma. It seems likely that azumolene does not alter the sarcoplasmic reticulum function such as Ca2 uptake and release in cardiac muscle.