| Objective:Exercise takes a two-sided effect on the heart.Exhaustive exercise can lead to a series of cardiac injury,such as the fracture of myocardial fiber,the enhancement of oxidative stress response and inflammatory response,and the dysfunction of cardiac conduction.To fight against this heart injury,the exercise preconditioning plays an important role on heart protection.The exercise preconditioning can make the heart change the structural adaptability and improve the heart conduction function.Moreover,the exercise preconditioning can also enhance the antioxidant capacity and reduce the inflammatory response.The exercise heart protection mechanism in improving the cardiac conduction function of inhibiting CaMKⅡ-RyR2 signaling pathways activated in reducing exhaustion caused by plays an important role in the occurrence of arrhythmia but few studies in the field of sports medicine.Therefore,this research through the establishment of exercise model in rats,one-time exhaustion exercise as traumatic stimulus,and use the CaMKⅡ inhibitors KN-93 as a comparison.The concern from electrocardiogram(ecg),myocardial structure,the incidence of arrhythmia and myocardial calcium regulation related proteins,to explore the effect of exercise preconditioning on CaMKⅡ-RyR2 signaling pathway on the incidence of arrhythmias in exhaustive rats and its molecular mechanism.Methods:1 Establishment of animal models120 healthy male SD rats were randomly divided into 8 groups(n = 15): the control group(C),exercise exhaustion group(EE),exercise preconditioning group(EP),exercise preconditioning + exercise exhaustion group(EP+EE),KN-93 group(K),exercise exhaustion + KN-93 group(EE+K),exercise preconditioning + KN-93 group(EP + K),exercise preconditioning + exercise exhaustion +KN-93 group(EE + EP + K).According to Lennon and Domenech’s test methods of exercise training,a model of exercise preconditioning and exhaustion was established.Group EP,EP+K,EP+EE and EP+EE+K were given platform running training before the exercise exhaustion,with a slope of 0° and a speed of 25 m/min.They exercised for 15 min and rested for 5 min,repeated 3 times,and exercised 6 days a week for a total of 3 weeks.After 3 weeks,the EP+EE,EE,EE+K and EP+EE+K were treated with a slope of 0° and a speed of 30~35 m/min for exhaustive exercise.In the EE+K group and EP+EE+K group,KN-93(3.327×10-3mmol/kg)was intraperitoneally injected 30 minutes before exhaustion,while in the EP+K group and K group,the anesthesia electrocardiogram collection and other follow-up steps were performed 2 hours after KN-93 injection.2.The myocardial microstructure of rats was observed by light microscope after HE staining.3.Physiological recorder was used to record ECG and observe ECG changes.Heart rate,QRS interval,ST height,RR interval,PR interval,QT interval and other parameters of each group were recorded.4.Rats arrhythmia was induced by electrostimulation of electrode catheter through esophagus,and the occurrence of arrhythmia in each group was observed.5.The protein contents of CaMKⅡ,p-CaMKⅡ,RyR2,p-RyR2(S2814),PLN-Thr17,PLN,PP1 and SERCA2 a in left ventricular myocardium of rats were detected by Western blot.Results:1 Comparison of exhaustion time of rats in each group.Compared with the EE group,the exhaustion time of the EP+EE group and the EP+EE+KN group was significantly longer,the difference was statistically significant(P < 0.05).Compared with the EE+KN group,the exhaustion time of the EP+EE group and the EP+EE+KN group was significantly longer,the difference was statistically significant(P < 0.05).We can see that the average exhaustion time of the rats receiving EP training was significantly prolonged.EP can improve the endurance of rats and enhance the tolerance to strenuous exercise.2 The results of light microscope observation of myocardial tissue structure in ratsThere was no significant change in myocardial in groups C,C+K,EP and EP+K.In the EE group,there were obvious swelling,rupture,necrosis and uneven staining of myocardial cells,and multiple breaks,disordered arrangement and infiltration of inflammatory cells were observed in the myocardial fiber structure.The myocardial structure of EP+EE group and EE+K group was significantly improved compared with EE group.The myocardial structure and injury of rats in EP+EE+K group were less than those in EP+EE and EE+K group.3.Comparison of ECG indexes of rats in each groupcompared with the EE+KN group,the heart rate of the EP+K group,the C group,the EP group and the EP+EE group were slower,and the difference was significant(P < 0.05).Compared with the EE group,the heart rate of the EP+KN group and the EP group was also slower,and the difference was significant(P < 0.05).Compared with the EE+KN group,the RR interval of the C group and the EP+KN group was relatively longer,and the difference was significant(P < 0.05).Compared with the EE+KN group,the PR interval in the C,C+KN and EP+KN group was relatively longer,and the difference was significant(P < 0.05).Compared with the EE+KN group,the EP+EE group had longer QT interval,and the difference was significant(P < 0.05).4.Comparison of the incidence of arrhythmia in each groupIn terms of the incidence of arrhythmia,6 cases(40%)were found in group C,3 cases(20%)in group C+K,4 cases(26.67%)in group EP,2 cases(13.33%)in group EP+K,11 cases(73.33%)in group EE,5 cases(33.33%)in group EE+K,7 cases(46.67%)in group EP+EE,and 3 cases(20%)in group EP+EE+K.Compared with group C,the incidence of arrhythmia was significantly increased in the group EE,and it was significantly decreased in the group C+ group and group EP+EE+K,and the difference was significant(P < 0.05).Compared with the EP group,the incidence of arrhythmia was significantly decreased in the EE group and EP+EE group(P < 0.05).Compared with group EE,the incidence of arrhythmia was significantly decreased,and the difference was significant in each group(P < 0.05).Compared with group EP+EE+K,the incidence of arrhythmia was significantly increased in group EP+EE,and the difference was significant(P < 0.05).5.Comparison of the contents of CaMKⅡ,p-CaMKⅡ,RyR2,p-RyR2(S2814),PLN,p-PLN,SERCA2 a and PP1 in myocardium of rats in each group.5.1.1 Comparison of CaMKⅡ and p-CaMKⅡ protein contents in left ventricular myocardium of rats in each groupCompared with group C,the contents of CaMKⅡ and p-CaMKⅡ in the myocardium of rats in the EE group were significantly increased,while the contents of CaMKⅡ and p-CaMKⅡ in the EP group were significantly decreased,with P < 0.05 indicating statistical significance.The results showed that the contents of CaMKⅡ and p-CaMKⅡ in the EE group were the highest in each group,and the contents of CaMKⅡ and p-CaMKⅡ in the EP+EE group,EP group and EE+K group were significantly decreased compared with the EE group,with statistical significance(P < 0.05).Compared with the EP+EE+K group,the content of CaMKⅡ and p-CaMKⅡ in the EP+EE group was significantly increased,and the content of CaMKⅡ in the EE+K group was significantly increased,with P < 0.05,which was statistically significant.Compared with C+K group,the content of CaMKⅡ in group C was significantly increased,P < 0.05 was statistically significant;There was an increase in p-CaMKⅡ,but there was no statistically significant difference.5.1.2 Comparison of RyR2,p-RyR2(S2814)protein contents in left ventricular myocardium of rats in each groupCompared with the C group,the contents of RyR2 and p-RyR2(S2814)in the myocardium of rats in the EE group were significantly increased,while the contents of RyR2 and p-RyR2(S2814)in the EP group were significantly decreased,and the contents of p-RyR2(S2814)in the C+K group were significantly increased,all with statistical significance(P < 0.05).The contents of RyR2 and p-RyR2(S2814)in the EP+EE group and EP group were significantly decreased compared with the EE group,with statistically significant(P < 0.05).Compared with the EP+EE+K group,the content of p-RyR2(S2814)was significantly increased in the EP+EE and EE+K groups,with statistical significance(P < 0.05).5.2 Comparison of protein contents of PLN,p-PLN,SERCA2 a and PP1 in left ventricular myocardium of rats in each group5.2.1 Comparison of the contents of PLN and P-PLN related to calcium ion regulation among each groupCompared with group C,the contents of calciumion regulation-related proteins PLN and p-PLN in myocardium of rats in the EE group were significantly increased,while the content of p-PLN protein in the C+K group was significantly decreased,with statistical significance(P < 0.05).Compared with the EE group,the content of PLN and P-PLN protein in the EP group was significantly decreased,and the difference was statistically significant.Compared with EP+EE group,p-PLN protein content in EP+EE+K group was significantly decreased,and the difference was statistically significant(P < 0.05).5.2.2 Comparison of the contents of calcium-regulated proteins SERCA2 a and PP1 among each group.Compared with group C,the content of SERCA2 a in myocardium of rats in the EE group and C+K group was significantly decreased,and the content of PP1 in the EE group was significantly increased.SERCA2 a content was significantly increased and PP1 content was significantly decreased in EP group,with statistical significance(P < 0.05).Compared with the EE group,the content of SERCA2 a in the EP group,the EP+EE group,the EE+K group and the EP+EE+K group was significantly increased,and the PP1 content in the EP group and the EP+EE+K group was significantly decreased,the difference being statistically significant(P < 0.05).Compared with EP+EE+K group,the PP1 protein content in EE+K group was significantly increased,while the PP1 protein content in EP+K group was significantly decreased,with statistical significance(P < 0.05).Conclusion:1.Exhaustive exercise damages the myocardial structure of rats and causes cardiac conduction dysfunction.Exhaustive exercise increases the susceptibility of arrhythmias byactivating the CaMKⅡ-RyR2 signaling pathway and reducing the content of SERCA2 a.2.Exercise preconditioning could reduce the myocardial damage caused by exhaustive exercise.Exercise preconditioning improve the myocardial electrical activity disturbance,and reduce the susceptibility to arrhythmias by inhibiting the CaMKⅡ-RyR2 signaling pathway and increase the content of SERCA2 a.3.Exercise preconditioning through inhibition of CaMKⅡ-RyR2 signaling pathways,reduce RyR2 in S2814 phosphorylation sites,thus reduce the degree of Ca2 + leak,give play to the role of anti-arrhythmic protection. |
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