TRPV4 Blockade Suppresses Atrial Fibrillation Through Alleviating Electrical Remodeling And Calcium Handling Abnormalities In Sterile Pericarditis Rats

Part ? TRPV4 blockade improves vulnerability to atrial fibrillation and atrial electrical remodeling in sterile pericarditis ratsObjective: Recent studies have found that TRPV4 plays an important role in cardiovascular disease.Previously,we found that the expression and function of TRPV4 are upregulated in atrial fibrillation(AF)patients and a sterile pericarditis(SP)rat model of AF,and an oral TRPV4 inhibitor(GSK2193874)alleviates AF in SP rats.However,how TRPV4 participates in atrial electrical remodeling in SP rats has not been thoroughly studied.The aim of this study was to investigate whether an oral GSK2193874 alleviated vulnerability to AF and atrial electrical remodeling in SP rats.Method: A SP rat model of AF was established by daubing sterile talcum powder on both atria of male Sprague-Dawley(SD)rats,after a pericardiotomy,to simulate the pathogenesis of postoperative atrial fibrillation(POAF).SP rats were treated with GSK2193874(10 mg/kg/day)or same solvent via oral gavage for 3 days,regarded as GSK2193874 group and vehicle group,respectively.SD rats subjected to the same procedure without pericardiotomy(sham group)were used as basal control.On the 3rd postoperative day,action potential(AP)signals of atria were collected in isolated perfused hearts by optical mapping.The susceptibility to AF and atrial effective refractory period(ERP)were tested by a S1S2 stimulus method.The electrophysiological parameters,including atrial action potential duration(APD)and its regional heterogeneity,were quantified at a pacing rate(PR)of 7 Hz.Atrial conduction velocity was detected at a series of PRs from 7 to 18 Hz.Result: Compared with sham rats,the hearts of vehicle-treated rats exhibited more frequent atrial ectopy or fibrillation in response to S1S2 stimulation,which was prevented after treatment with GSK2193874.During the onset of AF in the vehicle group,triggered activity and reentrant activity could be seen on the atrial surface.However,no difference in atrial ERP was detected among the 3 groups.The APD in the vehicle group was prolonged significantly at a PR of 7 Hz,accompanying by more obvious regional heterogeneity.The abnormal prolongation and the regional heterogeneity were reversed by treatment with GSK2193874.However,there was no significant difference in time to peak and atrial conduction velocity among the 3 groups.Conclusion: An oral TRPV4 inhibitor alleviates atrial electrical remodeling in SP rats,including the improvement of prolongation and regional heterogeneity of APD,reduces atrial ectopy and reentrant activity,and thus relieves vulnerability to AF,contributing to the treatment of POAF.Part ? TRPV4 blockade improves atrial ion channel remodeling in sterile pericarditis ratsObjective: The generation of cardiac AP depends on the sequential opening and closing of various voltage-dependent ion channels that span the plasma membrane of individual myocytes.When ion channel remodeling occurs in atrial myocytes,electrical remodeling with major change of AP occurs.To date,TRPV4 activation has been reported to modulate some ion currents in neurons.Therefore,this study further explored whether TRPV4 blockade alleviated delay in AP repolarization in SP rats by regulating one or more voltage-dependent ion channels.Method: A SP rat model of AF was established by daubing sterile talcum powder on both atria of male SD rats,after a pericardiotomy,to simulate the pathogenesis of POAF.SP rats were treated with GSK2193874(10 mg/kg/day)or same solvent via oral gavage for 3 days,regarded as GSK2193874 group and vehicle group,respectively.SD rats subjected to the same procedure without pericardiotomy(sham group)were used as basal control.On the3 rd postoperative day,atrial myocytes were isolated.APD,as well as current density and kinetic parameters of related voltage-dependent ion channels,were quantified by using the patch-clamp technique.Result: Compared with the sham group,transient outward potassium current(I_to)and steady-state outward potassium current(I_ss)of atrial myocytes in the vehicle group were significantly decreased.However,there was no significant difference in the steady-state inactivation and recovery after inactivation of I_to between the sham group and the vehicle group.Inwardly rectifying potassium current(I_k1)did not differ between the 2 groups.L-type calcium current(I_Ca,L)of atrial myocytes in the vehicle group decreased significantly,and its steady-state inactivation curve was shifted to the right,compared with the sham group.However,the activation curve of I_Ca,L did not alter.And yet,there were no significant differences in sodium current(I_Na),activation and steady-state inactivation of I_Na,and recovery after inactivation of I_Na between the sham group and the vehicle group.Compared with the vehicle group,prolongation of APD as well as reduction of I_to and I_ss,were alleviated in the GSK2193874 group.However,there was no significant difference in resting membrane potential(RMP),AP amplitude(APA),or maximum upstroke slope of AP(Vmax)among the 3 groups.Conclusion: The prolongation of APD in atrial myocytes of SP rats is a result of comprehensive effect of remodeling of various ion channels,in which I_to and Iss play a crucial role.An oral TRPV4 inhibitor improves atrial electrical remodeling by mitigating voltage-dependent potassium channel remodeling and thus reverses the prolongation of APD.Part ? TRPV4 blockade improves atrial calcium handling abnormalities in sterile pericarditis ratsObjective: Atrial altered calcium(Ca²⁺)handling plays a role in the pathogenesis of AF.Previously,we found that the expression and function of TRPV4 are upregulated in AF patients and a SP rat model of AF,and an oral GSK2193874 alleviates AF in this animal model.However,whether TRPV4,as a Ca²⁺ channel,is involved in atrial Ca²⁺ handling abnormalities in this animal model has not been studied.The aim of this study was to investigate whether an oral GSK2193874 alleviated atrial Ca²⁺ handling abnormalities in SP rats.Method: A SP rat model of AF was established by daubing sterile talcum powder on both atria of male SD rats,after a pericardiotomy,to simulate the pathogenesis of POAF.SP rats were treated with GSK2193874(10 mg/kg/day)or same solvent via oral gavage for 3 days,regarded as GSK2193874 group and vehicle group,respectively.SD rats subjected to the same procedure without pericardiotomy(sham group)were used as basal control.On the3 rd postoperative day,Ca²⁺ signals of atria were collected in isolated perfused hearts by optical mapping.Ca²⁺ transient duration(CaD)was quantified at a PR of 7 Hz.To induce alternan,continuous pacing at progressively faster frequencies from 8 to 18 Hz was performed.To assess the restitution properties of Ca²⁺ transient(CaT),an S1S2 stimulus method was implemented.Result: At a PR of 7 Hz,CaD and time to peak were prolonged significantly,accompanying by more obvious regional heterogeneity of CaD in the atria of vehicle-treated rats,compared with sham rats.The abnormal prolongation and the regional heterogeneity were reversed by treatment with GSK2193874.Compared with the sham group,the PR threshold to develop Ca²⁺ transient alternan(Ca-ALT)and APD alternan(APD-ALT)in the vehicle group was decreased to 9 Hz.With increasing PR,CA-ALT and APD-ALT in the vehicle group became more serious.However,CA-ALT and APD-ALT were significantly relieved in the GSK2193874 group.In the vehicle group,atrial T-wave alternan(Ta-ALT)of ECG recorded simultaneously was frequently found in the vehicle group at a PR of 9 Hz,which was hardly found in the sham group and the GSK2193874 group.When the PR reached 16-18 Hz,Ca-ALT in the vehicle group became spatially discordant.Compared with the sham group,the incidence of discordant alternan(DIS-ALT)in the vehicle group was higher,which was significantly reduced in the GSK2193874 group.Compared with the sham group,the S2/S1 CaT ratio was significantly decreased at all S2 intervals below 130 ms in the vehicle group,suggesting a delay in ryanodine receptor(RyR)refractoriness.Treatment with GSK2193874 prevented the reduction in the S2/S1 CaT ratio.Coefficient of variation(COV)of S2/S1 CaT ratio(COV ratio)was further quantified.Compared with the sham group,the COV ratio was dramatically up-regulated in the vehicle group.However,the COV ratio was reversed in the GSK2193874 group.In addition,the most obvious region of alternan was found to be the starting site of triggered activity and reentrant activity in the atrium of vehicle group during the onset of AF,reflecting the arrhythmogenic effect of alternan.Conclusion: The dysfunction of RyR and sarcoplasmic reticulum Ca²⁺-ATPase(SERCA)in SP rats lead to atrial Ca²⁺ handling abnormalities,including sarcoplasmic reticulum(SR)Ca²⁺ release abnormalities and Ca²⁺ uptake abnormalities,contributing to susceptibility to arrhythmogenic alternan.A delay in RyR refractoriness,namely SR Ca²⁺ release abnormalities,is mainly responsible for the onset of alternan.And an oral TRPV4 inhibitor alleviates Ca²⁺ handling abnormalities primarily by blocking the TRPV4-Ca²⁺-RyR pathway,and thus exerts therapeutic effect on POAF.