Effect Of Hypothermic Ischemia-reperfusion On Conduction Velocity Of Isolated Rat Atrium And Its Related Mechanism

Objectives:To observe the effect of hypothermic ischemia-reperfusion on the conduction velocity of isolated rat atrium,and to explore the role of connexin 40(Cx40)and connexin 43(Cx43)protein expression in it.Methods:Sixteen healthy adult male SD rats weighing 320-380 g were successfully made into langendorff isolated heart perfusion models and were randomly divided into control group(Group C)and ischemia-reperfusion group(Group I/R),8 in each group.According to the occurrence of atrial arrhythmia after reperfusion,Group I/R was further divided into reperfusion no atrial arrhythmia subgroup(Group R-NAA)and reperfusion atrial arrhythmia subgroup(Group R-AA).Group C was continuous perfusion with K-H solution(37℃)for 120 minutes.In Group I/R,K-H solution(37℃)was used to perfuse for 30 minutes and then stopped;Thomas solution(4℃,20ml/kg)was injected to make the cardiac arrest for 60 minutes,the heart was protected by hypothermia(4℃)K-H solution,and half of Thomas solution(4℃,10ml/kg)was injected again after 30 minutes of cardiac arrest,then K-H solution(37℃)was reperfused for 30 min after 60 minutes of cardiac arrest.Right atrial monophasic action potentials was recorded at 30 min of continuous perfusion(T0),105 min of continuous perfusion/15 min of reperfusion(T1),and 120 min of continuous perfusion/30 min of reperfusion(T2),and the d V/dtmax of phase 0(Vmax)were mearsured.The type of atrial arrhythmia,duration and incidence of reperfusion atrial arrhythmia were recorded from the moment of reperfusion to the end of reperfusion.The effective refractory period(ERP)and conduction velocity(CV)of the right atrium were measured and the activation wavelength(λ)was calculated at T2.The expression of Cx40 and Cx43 in the right atrial myocardium was detected by Western blotting,and the ratio of Cx40 to Cx40+Cx43 [Cx40/(Cx40+Cx43)]and the ratio of Cx43 to Cx40+Cx43[Cx40/(Cx40+Cx43)] were calculated.Results:(1)The occurrence of reperfusion atrial arrhythmia in isolated rat heart: 3 cases in Group I/R had different degrees of atrial arrhythmia,including 2 cases of atrial fibrillation and 1 case of atrial premature beat;the duration of arrhythmia was 305 s,288 s and 358 s respectively,and the incidence of reperfusion atrial arrhythmia was about 38%.(2)Vmax: Compared with T0,Vmax at T1 in Group R-AA decreased(P<0.05),and compared with Group C and Group R-NAA,Vmax in Group R-AA decreased at T1(P<0.05).(3)ERP: Compared with Group C,ERP was prolonged in Group R-NAA and Group R-AA(P<0.05),and ERP in Group R-AA was prolonged compared with Group R-NAA(P<0.05).(4)CV: Compared with Group C,CV decreased in Group R-NAA and Group R-AA(P<0.05),and CV decreased in Group R-AA compared with Group R-NAA(P<0.05).(5)λ:There was no significant difference in λ among groups(P>0.05).(6)The expression of Cx40 and Cx43:Compared with Group C,the expression of Cx40 and Cx43 was decreased in Groups R-NAA and R-AA(P<0.05);Compared with Group R-NAA,the expression of Cx40 and Cx43 was decreased in Group R-AA(P<0.05).(7)Cx40/(Cx40+Cx43): The ratio of Cx40/(Cx40+Cx43)in Groups R-NAA and R-AA was higher than that in Group C(P < 0.05),and the ratio of Cx40/(Cx40+Cx43)in Group R-AA was higher than that in Group R-NAA(P<0.05).(8)Cx43/(Cx40+Cx43): The ratio of Cx43/(Cx40+Cx43)in Group R-NAA and R-AA was lower than that in Group C(P<0.05),and the ratio of Cx43/(Cx40+Cx43)in Group R-AA was lower than that in Group R-NAA(P<0.05).Conclusions:(1)The conduction velocity of isolated rat atrium decreased after hypothermic ischemia-reperfusion;(2)The decrease of conduction velocity in isolated rat atrium after hypothermic ischemia-reperfusion may be related to the down-regulation of Cx40 and Cx43 expression.