A New Target For Treatment And Prevention Of Calcium Related Arrhythmia:Store Overload Induced Calcium Release (SOICR)

Objections:Store overload induced calcium release (SOICR) plays an import role in catecholaminergic polymorphic ventricular tachycardia and heart failure. In this study we will develop a model of SOICR in pacing cardiomyocytes, and observe the effect of carvedilol and verapamil on SOICR in pacing cardiomyocytes respectively. To observe the effect of verapamil on the frequency of ventricular arrhythmia in rats with SOICR, we develop a model of rats with SOICR and investigate the role of verapamil in triggered ventricular arrhymia.Methods:The research includes three parts as the following:(1) To observe the effect of carvedilol on store overload-induced calcium release in pacing cardiomyocytes:The cardiomyocytes were assigned into control group, carvedilol group, metoprolol group, phentolamine group and nifedipine group. Single rat cardiomyocyte was perfused with isoprenaline and caffeine with rapid pacing to induce calcium overload. Spontaneous calcium releases through sarcoplamic reticulum calcium release channel (ryanodine receptor type2, RyR2) were investigated in fluorescent imaging study.(2) To observe the effect of verapamil on store overload-induced calcium release and ryanodine receptor in cardiomyocytes in pacing cardiomyocytes:The cardiomyocytes were assigned into control group, verapamil group and nifedipine group. Single rat cardiomyocyte was perfused with isoprenaline and caffeine with rapid pacing to induce calcium overload. Spontaneous calcium releases through sarcoplamic reticulum calcium release channel RyR2were investigated in fluorescent imaging study. Impaction of verapamil on single native RyR2channels from sarcoplasmic reticulum microsomes fused into lipid bilayers was assessed.(3) To observe the effect of verapamil on ventricular tachycardia in rats with store overload induced calcium release:Sprague Dawley rats were randomly divided into three groups: the control group, the verapamil group (1.5mg/kg) and the nifedipine group (0.5mg/kg). The rats received intraperitoneal injection of drugs20minutes in advance. Then rats were injected with isoprenaline and caffeine. The incidence of triggered activity, ventricular tachycardia and spontaneous ventricular arrhythmias were recorded with rapid pacing.Results:(1) The incidence of SOICR in carvedilol group was significantly lower than that in control group at the pacing frequency of1Hz to4Hz (P<0.01). The inhibitory effect of carvedilol was not significantly different at variant pacing frequency (P>0.05). The incidences of SOICR in metoprolol group, phentolamine group and nifedipine group had no significant difference compared with control group (P>0.05). The amplitude of calcium transient and caffeine peak of pacing cardiomyocytes had no significant difference between different groups (P>0.05).(2) The amplitudes of calcium transient and caffeine peaks of pacing cardiomyocytes in verapamil group and nifedipine group were significantly lower than that in control group (P<0.05). The incidences of SOICR in verapamil group and nifedipine group were significantly lower than that in control group (P＜0.05). The inhibitory effect of verapamil on SOICR was better than nifedipine (from1to3Hz, P＜0.05). Verapamil directly reduced the open duration of the cardiac RyR2channel (P＜0.05).(3) In control group, the incidence of triggered activity and ventricular arrhythmias were significantly increased under the condition of injecting with isoprenaline and caffeine with rapid pacing. Compared with control group, verapamil significantly decreased the incidence of ventricular arrhythmias in rats with SOICR at rapid pacing. The incidence of ventricular arrhythmias occurred in6/6and2/8rats in the control group and verapamil group respectively (P<0.05). But the inhibitory effect was not found in nifedipine group (5/6). The incidence of spontaneous ventricular arrhythmias in the verapamil group was significant higher than that in control group, occurred in1/8and5/6rats in the two groups respectively (P<0.05).Conclusions:Carvedilol effectively suppresses SOICR in pacing cardiomyocytes due to its direct inhibition on the spontaneous opening of cardiac RyR2channel. Verapamil effectively suppresses SOICR in pacing cardiomyocytes and SOICR induced ventricular arrhythmia by directly reducing the open duration of the cardiac RyR2channel combined with its L type calcium channel blocking activity, which would probably contribute to its favorable antiarrhythmic effect.